Dysgeusia
Encyclopedia
Dysgeusia is the distortion of the sense of taste. Dysgeusia is also often associated with ageusia
, which is the complete lack of taste, and hypogeusia
, which is the decrease in taste sensitivity. An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary symptom
. The distortion in the sense of taste is the only symptom, and diagnosis
is usually complicated since the sense of taste is tied together with other sensory systems. Common causes of dysgeusia include chemotheraphy, asthma treatment with albuterol, and zinc deficiency. Different drugs could also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms of dysgeusia. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.
and foliate papillae
are found on the posterior portion of the tongue. The salivary glands are responsible for keeping the taste buds moist with saliva.
A single taste bud is composed of four different types of cells, and each taste bud has at least 30 to 80 cells. Type I cells are thinly shaped, usually in the periphery of other cells. They also contain high amounts of chromatin
. Type II cells have prominent nuclei
and nucleoli with much less chromatin than Type I cells. Type III cells have multiple mitochondria and large vesicles
. Type I, II, and III cells also contain synapses. Type IV cells are normally rooted at the posterior end of the taste bud. Every cell in the taste bud forms microvilli at the ends.
In humans, the sense of taste is conveyed via three of the twelve cranial nerves
. The facial nerve
(VII) is responsible for taste sensations from the anterior two thirds of the tongue, the glossopharyngeal nerve
(IX) is responsible for taste sensations from the posterior one third of the tongue while a branch of the vagus nerve
(X) carries some taste sensations from the back of the oral cavity.
, usually a metallic taste, and sometimes smell
are the only symptoms. The duration of the symptoms of dysgeusia depends on the cause. If the alteration in the sense of taste is due to gum disease, dental plaque
, a temporary medication, or a short-term condition such as a cold
, the dysgeusia should disappear once the cause is removed. In some cases, if lesions are present in the taste pathway and nerves have been damaged, the dysgeusia may be permanent.
, the somatosensory system
, and the perception of pain
(such as in tasting spicy foods), it is difficult to examine sensations mediated through an individual system. In addition, gustatory dysfunction is rare when compared to olfactory disorders.
Diagnosis of dysgeusia begins with the patient being questioned about salivation, swallowing, chewing, oral pain, previous ear infections (possibly indicated by hearing or balance problems), oral hygiene, and stomach problems. The initial history assessment also considers the possibility of accompanying diseases such as diabetes mellitus
, hypothyroidism
, or cancer
. A clinical examination is conducted and includes an inspection of the tongue and the oral cavity. Furthermore, the ear canal
is inspected, as lesions of the chorda tympani
have a predilection for this site.
Threshold
tests for sucrose
(sweet), citric acid
(sour), sodium chloride
(salty), and quinine
or caffeine
(bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test." In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water. Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row.
Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour). Direct scaling cannot be used to determine if a taste stimulus is being perceived at abnormal levels. In this case, magnitude matching is used, in which a patient is asked to rate the intensities of taste stimuli and stimuli of another sensory system
, such as the loudness of a tone, on a similar scale. For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones. Assuming normal hearing, the results of this cross-sensory test show the relative strength of the sense of taste in relation to the loudness of the auditory stimulus. Although many of the tests are based on ratings using the direct scaling method, some tests do use the magnitude-matching procedure.
Other tests include identification or discrimination of common taste substances. Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily. In addition to techniques based on the administration of chemicals to the tongue, electrogustometry is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical direct current
. Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue. Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.
tests and simple reflex tests may be applied to identify abnormalities in the nerve
-to-brainstem pathways. For example, the blink reflex may be used to evaluate the integrity of the trigeminal nerve
–pontine brainstem
–facial nerve
pathway, which may play a role in gustatory function.
Structural imaging is routinely used to investigate lesions in the taste pathway. Magnetic resonance imaging
allows direct visualization of the cranial nerves
. Furthermore, it provides significant information about the type and cause of a lesion. Analysis of mucosal blood flow
in the oral cavity in combination with the assessment of autonomous cardiovascular factors appears to be useful in the diagnosis of autonomic nervous system
disorders in burning mouth syndrome and in patients with inborn disorders, both of which are associated with gustatory dysfunction. Cell cultures may also be used when fungal or bacterial infections are suspected.
In addition, the analysis of saliva
should be performed, as it constitutes the environment of taste receptors
, including transport of tastes to the receptor and protection of the taste receptor. Typical clinical investigations involve sialometry and sialochemistry. Studies have shown that electron micrographs
of taste receptors obtained from saliva samples indicate pathological changes in the taste buds of patients with dysgeusia and other gustatory disorders.
. Chemotherapy often induces damage to the oral cavity, resulting in oral mucositis, oral infection, and salivary gland dysfunction. Oral mucositis consists of inflammation
of the mouth, along with sores and ulcers
in the tissues. Healthy individuals normally have a diverse range of microbial organisms residing in their oral cavities; however, chemotherapy can permit these typically non-pathogenic agents to cause serious infection, which may result in a decrease in saliva
. In addition, patients who undergo radiation therapy
also lose salivary tissues. Saliva is an important component of the taste mechanism. Saliva both interacts with and protects the taste receptors in the mouth. Saliva mediates sour and sweet tastes through bicarbonate ions and glutamate, respectively. The salt taste is induced when sodium chloride levels surpass the concentration in the saliva. It has been reported that 50% of chemotherapy patients have suffered from either dysgeusia or another form of taste impairment. Examples of chemotherapy treatments that can lead to dysgeusia are cyclophosphamide
, cisplatin
, and etoposide
. The exact mechanism of chemotherapy-induced dysgeusia is unknown.
and cytoplasm
of the taste bud cells have been reduced. Based on their findings, dygeusia results from loss of microvilli and the reduction of Type III intracellular vesicles, all of which could potentially interfere with the gustatory pathway.
deficiency. While the exact role of zinc in dysgeusia is unknown, it has been cited that zinc is partly responsible for the repair and production of taste buds. Zinc somehow directly or indirectly interacts with carbonic anhydrase VI, influencing the concentration of gustin, which is linked to the production of taste buds. It has also been reported that patients treated with zinc experience an elevation in calcium
concentration in the saliva. In order to work properly, taste buds rely on calcium receptors. Zinc “is an important cofactor for alkaline phosphatase
, the most abundant enzyme
in taste bud membranes; it is also a component of a parotid salivary protein important to the development and maintenance of normal taste buds.”
and emedastine
. Approximately 250 drugs affect taste. The sodium
channels linked to taste receptors can be inhibited by amiloride
, and the creation of new taste buds and saliva can be impeded by antiproliferative drugs. Saliva can have traces of the drug, giving rise to a metallic flavor in the mouth; examples include lithium carbonate
and tetracyclines. Drugs containing sulfhydryl groups, including penicillamine
and captopril
, may react with zinc and cause deficiency. Metronidazole
and chlorhexidine have been found to interact with metal ions that associate with the cell membrane
.
Drugs that prevent the production of angiotensin II by inhibiting angiotensin converting enzyme, eprosartan
for example, have been linked to dysgeusia.
, also known as dry mouth syndrome, can precipitate dysgeusia because normal salivary flow and concentration are necessary for taste. Injury to the glossopharyngeal nerve
can result in dysgeusia. In addition, damage done to the pons
, thalamus
, and midbrain, all of which compose the gustatory pathway, can be potential factors. In a case study, 22% of patients who were experiencing a bladder obstruction were also suffering from dysgeusia. Dysgeusia was eliminated in 100% of these patients once the obstruction was removed. Although it is uncertain what the relationship between bladder relief and dysgeusia entails, it has been observed that the areas responsible for urinary system
and taste in the pons and cerebral cortex
in the brain are close in proximity.
Many of the causes for dysgeusia are not fully understood, making idiopathic
dysgeusia very common. A wide range of miscellaneous factors may contribute to this taste disorder, such as gastric reflux, lead poisoning
, and diabetes mellitus
. A minority of pine nut
s can apparently cause taste disturbances, for reasons which are not entirely proven. Certain pesticides can have damaging effects on the taste buds and nerves in the mouth. These pesticides include organochloride
compounds and carbamate
pesticides. Damage to the peripheral nerves, along with injury to the chorda tympani
branch of the facial nerve, also cause dysgeusia. A surgical risk for laryngoscopy
and tonsillectomy
include dysgeusia. Patients who suffer from the burning mouth syndrome, most likely menopausal women, are often suffering from dysgeusia as well.
, or a decrease in saliva flow, can be a side effect of many drugs, which, in turn, can lead to the development of taste disturbances such as dysgeusia. Patients can lessen the effects of xerostomia with breath mints, sugarless gum, or lozenges, or physicians can increase saliva flow with artificial saliva or oral pilocarpine
. Artificial saliva mimics the characteristics of natural saliva by lubricating and protecting the mouth but does not provide any digestive or enzymatic benefits. Pilocarpine is a cholinergic
drug meaning it has the same effects as the neurotransmitter
acetylcholine
. Acetylcholine has the function of stimulating the salivary glands to actively produce saliva. The increase in saliva flow is effective in improving the movement of tastants to the taste buds.
. Many medications are known to chelate, or bind, zinc
preventing the element from functioning properly. Due to the causal relationship of insufficient zinc levels to taste disorders, research has been conducted to test the efficacy of zinc supplementation as a possible treatment for dygeusia. In a randomized clinical trial, fifty patients suffering from idiopathic
dysgeusia were given either zinc or a lactose placebo
. The patients prescribed the zinc reported experiencing improved taste function and less severe symptoms compared to the control group, suggesting that zinc may be a beneficial treatment. The efficacy of zinc, however, has been ambiguous in the past. In a second study, 94% of patients who were provided with zinc supplementation did not experience any improvement in their condition. This ambiguity is most likely due to small sample sizes and the wide range of causes of dysgeusia. A recommended daily oral dose of 25–100 mg appears to be an effective treatment for taste dysfunction provided that there are low levels of zinc in the blood serum
. There is not a sufficient amount of evidence to determine whether or not zinc supplementation is able to treat dysgeusia when low zinc concentrations are not detected in the blood.
experience disturbances in sensory perception such as dysgeusia. In a pilot study involving twelve lung cancer patients, chemotherapy drugs were infused with zinc in order to test its potential as a treatment. The results indicated that, after two weeks, no taste disturbances were reported by the patients who received the zinc-supplemented treatment while most of the patients in the control group who did not receive the zinc reported taste alterations. A multi-institutional study involving a larger sample size of 169 patients, however, indicated that zinc-infused chemotherapy did not have an effect on the development of taste disorders in cancer patients. An excess amount of zinc in the body can have negative effects on the immune system
, and physicians must use caution when administering zinc to immunocompromised cancer patients. Because taste disorders can have detrimental effects on a patient's quality of life, more research needs to be conducted concerning possible treatments such as zinc supplementation.
The effects of drug-related dysgeusia can oftentimes be reversed by stopping the patient's regimen of the taste altering medication. In one case, a forty-eight-year-old woman who was suffering from hypertension
was being treated with valsartan
. Due to this drug's inability to treat her condition, she began taking a regimen of eprosartan
, an angiotensin II receptor antagonist
. Within three weeks, she began experiencing a metallic taste and a burning sensation in her mouth that ceased when she stopped taking the medication. When she began taking eprosartan on a second occasion, her dysgeusia returned. In a second case, a fifty-nine-year-old man was prescribed amlodipine
in order to treat his hypertension. After eight years of taking the drug, he developed a loss of taste sensation and numbness in his tongue. When he ran out of his medication, he decided not to obtain a refill and stopped taking amlodipine. Following this self-removal, he reported experiencing a return of his taste sensation. Once he refilled his prescription and began taking amlodipine a second time, his taste disturbance reoccurred. These two cases suggest that there is an association between these drugs and taste disorders. This link is supported by the "de-challenge" and "re-challenge" that took place in both instances. It appears that drug-induced dysgeusia can be alleviated by reducing the drug's dose or by substituting a second drug from the same class.
that is made naturally by human cells. It can also be administered in capsules or can be found in foods such as red meat, organ meats, and yeast. Like other antioxidants, it functions by ridding the body of harmful free radicals that can cause damage to tissues and organs. It has an important role in the Krebs cycle as a coenzyme leading to the production of antioxidants, intracellular glutathione
, and nerve-growth factors. Animal research has also uncovered the ability of ALA to improve nerve conduction velocity
. Because flavors are perceived by differences in electric potential
through specific nerves innervating the tongue, idiopathic dysgeusia may be a form of a neuropathy. ALA has proven to be an effective treatment for burning mouth syndrome spurring studies in its potential to treat dysgeusia. In a study of forty-four patients diagnosed with the disorder, one half was treated with the drug for two months while the other half, the control group, was given a placebo for two months followed by a two month treatment of ALA. The results reported show that 91% of the group initially treated with ALA reported an improvement in their condition compared to only 36% of the control group. After the control group was treated with ALA, 72% reported an improvement. This study suggests that ALA may be a potential treatment for patients and supports that full double blind randomized studies should be performed.
, malnutrition
, impaired immunity, and a decline in health. Patients diagnosed with dysgeusia must use caution when adding sugar and salt to food and must be sure not to over compensate for their lack of taste with excess amounts. Since the elderly are often on multiple medications, they are at risk for taste disturbances increasing the chances of developing depression
, loss of appetite, and extreme weight loss. This is cause for an evaluation and management of their dysgeusia. In patients undergoing chemotherapy, taste distortions can often be severe and make compliance with cancer treatment difficult. Other problems that may arise include anorexia
and behavioral changes that can be misinterpreted as psychiatric delusions regarding food. Symptoms including paranoia
, amnesia
, cerebellar malfunction, and lethargy can also manifest when undergoing histidine
treatment. This makes it critical that these patients' dysgeusia is either treated or managed in order to improve their quality of life.
is looking into the mechanisms underlying the key receptors on taste cells and applying this knowledge to the future of medications and artificial food products. Meanwhile, the Taste and Smell Clinic at the University of Connecticut Health Center
is integrating behavioral, neurophysiological, and genetic studies involving stimulus concentrations and intensities in order to better understand taste function. The purpose of these studies is to unearth the biological mechanisms underlying taste and to use this data to eliminate taste disorders in order to improve the lives of taste disorder sufferers.
Ageusia
Ageusia is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami . It is sometimes confused with anosmia - a loss of the sense of smell...
, which is the complete lack of taste, and hypogeusia
Hypogeusia
Hypogeusia is a reduced ability to taste things . The complete lack of taste is referred to as ageusia.Causes of hypogeusia include the chemotherapy drug bleomycin, an antitumor antibiotic....
, which is the decrease in taste sensitivity. An alteration in taste or smell may be a secondary process in various disease states, or it may be the primary symptom
Symptom
A symptom is a departure from normal function or feeling which is noticed by a patient, indicating the presence of disease or abnormality...
. The distortion in the sense of taste is the only symptom, and diagnosis
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
is usually complicated since the sense of taste is tied together with other sensory systems. Common causes of dysgeusia include chemotheraphy, asthma treatment with albuterol, and zinc deficiency. Different drugs could also be responsible for altering taste and resulting in dysgeusia. Due to the variety of causes of dysgeusia, there are many possible treatments that are effective in alleviating or terminating the symptoms of dysgeusia. These include artificial saliva, pilocarpine, zinc supplementation, alterations in drug therapy, and alpha lipoic acid.
Background
The sense of taste is based on the detection of chemicals by specialized taste cells in the mouth. The mouth, throat, larynx, and esophagus all have taste buds, which are replaced every ten days. Each taste bud contains receptor cells. Afferent nerves make contact with the receptor cells at the base of the taste bud. A single taste bud is innervated by several afferent nerves, while a single efferent fiber innervates several taste buds. Fungiform papillae are present on the anterior portion of the tongue while circumvallate papillaeCircumvallate papillae
The circumvallate papillae are dome-shaped structures on the human tongue that vary in number from eight to twelve....
and foliate papillae
Foliate papillae
Taste-buds, the end-organs of the gustatory sense, are scattered over the mucous membrane of the mouth and tongue at irregular intervals. They occur especially in the sides of the vallate papillae. There is a localized area at the side of the base of the tongue, the foliate papillae, in which they...
are found on the posterior portion of the tongue. The salivary glands are responsible for keeping the taste buds moist with saliva.
A single taste bud is composed of four different types of cells, and each taste bud has at least 30 to 80 cells. Type I cells are thinly shaped, usually in the periphery of other cells. They also contain high amounts of chromatin
Chromatin
Chromatin is the combination of DNA and proteins that make up the contents of the nucleus of a cell. The primary functions of chromatin are; to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis and meiosis and prevent DNA damage, and to control gene...
. Type II cells have prominent nuclei
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
and nucleoli with much less chromatin than Type I cells. Type III cells have multiple mitochondria and large vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
. Type I, II, and III cells also contain synapses. Type IV cells are normally rooted at the posterior end of the taste bud. Every cell in the taste bud forms microvilli at the ends.
In humans, the sense of taste is conveyed via three of the twelve cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
. The facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
(VII) is responsible for taste sensations from the anterior two thirds of the tongue, the glossopharyngeal nerve
Glossopharyngeal nerve
The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
(IX) is responsible for taste sensations from the posterior one third of the tongue while a branch of the vagus nerve
Vagus nerve
The vagus nerve , also called pneumogastric nerve or cranial nerve X, is the tenth of twelve paired cranial nerves...
(X) carries some taste sensations from the back of the oral cavity.
Symptoms
The alterations in the sense of tasteTaste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
, usually a metallic taste, and sometimes smell
Smell
Smell may refer to:* Olfaction, sense of smell, the ability of humans and other animals to perceive odors* Odor, the percept resultant from the sense of smell...
are the only symptoms. The duration of the symptoms of dysgeusia depends on the cause. If the alteration in the sense of taste is due to gum disease, dental plaque
Dental plaque
Dental plaque is a biofilm, usually a pale yellow, that develops naturally on the teeth. Like any biofilm, dental plaque is formed by colonizing bacteria trying to attach themselves to a smooth surface...
, a temporary medication, or a short-term condition such as a cold
Common cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...
, the dysgeusia should disappear once the cause is removed. In some cases, if lesions are present in the taste pathway and nerves have been damaged, the dysgeusia may be permanent.
Diagnosis
In general, gustatory disorders are challenging to diagnose and evaluate. Because gustatory functions are tied to the sense of smellSmell
Smell may refer to:* Olfaction, sense of smell, the ability of humans and other animals to perceive odors* Odor, the percept resultant from the sense of smell...
, the somatosensory system
Somatosensory system
The somatosensory system is a diverse sensory system composed of the receptors and processing centres to produce the sensory modalities such as touch, temperature, proprioception , and nociception . The sensory receptors cover the skin and epithelia, skeletal muscles, bones and joints, internal...
, and the perception of pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
(such as in tasting spicy foods), it is difficult to examine sensations mediated through an individual system. In addition, gustatory dysfunction is rare when compared to olfactory disorders.
Diagnosis of dysgeusia begins with the patient being questioned about salivation, swallowing, chewing, oral pain, previous ear infections (possibly indicated by hearing or balance problems), oral hygiene, and stomach problems. The initial history assessment also considers the possibility of accompanying diseases such as diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
, hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
, or cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
. A clinical examination is conducted and includes an inspection of the tongue and the oral cavity. Furthermore, the ear canal
Ear canal
The ear canal , is a tube running from the outer ear to the middle ear. The human ear canal extends from the pinna to the eardrum and is about 35 mm in length and 5 to 10 mm in diameter....
is inspected, as lesions of the chorda tympani
Chorda tympani
The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the Stylomastoid foramen...
have a predilection for this site.
Gustatory testing
In order to further classify the extent of dysgeusia and clinically measure the sense of taste, gustatory testing may be performed. Gustatory testing is performed either as a whole-mouth procedure or as a regional test. In both techniques, natural or electrical stimuli can be used. In regional testing, 20 to 50 µL of liquid stimulus is presented to the anterior and posterior tongue using a pipette, soaked filter-paper disks, or cotton swabs. In whole mouth testing, small quantities (2-10 mL) of solution are administered, and the patient is asked to swish the solution around in the mouth.Threshold
Sensory threshold
Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation...
tests for sucrose
Sucrose
Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
(sweet), citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
(sour), sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
(salty), and quinine
Quinine
Quinine is a natural white crystalline alkaloid having antipyretic , antimalarial, analgesic , anti-inflammatory properties and a bitter taste. It is a stereoisomer of quinidine which, unlike quinine, is an anti-arrhythmic...
or caffeine
Caffeine
Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants...
(bitter) are frequently performed with natural stimuli. One of the most frequently used techniques is the "three-drop test." In this test, three drops of liquid are presented to the subject. One of the drops is of the taste stimulus, and the other two drops are pure water. Threshold is defined as the concentration at which the patient identifies the taste correctly three times in a row.
Suprathreshold tests, which provide intensities of taste stimuli above threshold levels, are used to assess the patient's ability to differentiate between different intensities of taste and to estimate the magnitude of suprathreshold loss of taste. From these tests, ratings of pleasantness can be obtained using either the direct scaling or magnitude matching method and may be of value in the diagnosis of dysgeusia. Direct scaling tests show the ability to discriminate among different intensities of stimuli and whether a stimulus of one quality (sweet) is stronger or weaker than a stimulus of another quality (sour). Direct scaling cannot be used to determine if a taste stimulus is being perceived at abnormal levels. In this case, magnitude matching is used, in which a patient is asked to rate the intensities of taste stimuli and stimuli of another sensory system
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
, such as the loudness of a tone, on a similar scale. For example, the Connecticut Chemosensory Clinical Research Center asks patients to rate the intensities of NaCl, sucrose, citric acid and quinine-HCl stimuli, and the loudness of 1000 Hz tones. Assuming normal hearing, the results of this cross-sensory test show the relative strength of the sense of taste in relation to the loudness of the auditory stimulus. Although many of the tests are based on ratings using the direct scaling method, some tests do use the magnitude-matching procedure.
Other tests include identification or discrimination of common taste substances. Topical anesthesia of the tongue has been reported to be of use in the diagnosis of dysgeusia as well, since it has been shown to relieve the symptoms of dysgeusia temporarily. In addition to techniques based on the administration of chemicals to the tongue, electrogustometry is frequently used. It is based on the induction of gustatory sensations by means of an anodal electrical direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
. Patients usually report sour or metallic sensations similar to those associated with touching both poles of a live battery to the tongue. Although electrogustometry is widely used, there seems to be a poor correlation between electrically and chemically induced sensations.
Diagnostic tools
Certain diagnostic tools can also be used to help determine the extent of dysgeusia. ElectrophysiologicalElectrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
tests and simple reflex tests may be applied to identify abnormalities in the nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
-to-brainstem pathways. For example, the blink reflex may be used to evaluate the integrity of the trigeminal nerve
Trigeminal nerve
The trigeminal nerve contains both sensory and motor fibres. It is responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing. Sensory information from the face and body is processed by parallel pathways in the central nervous system...
–pontine brainstem
Pontine nuclei
The pontine nuclei are a part of the pons involved in motor activity. Corticopontine fibres carry information from the primary motor cortex to the ipsilateral pontine nucleus in the ventral pons, and the pontocerebellar projection then carries that information to the contralateral cerebellum via...
–facial nerve
Facial nerve
The facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
pathway, which may play a role in gustatory function.
Structural imaging is routinely used to investigate lesions in the taste pathway. Magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
allows direct visualization of the cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves...
. Furthermore, it provides significant information about the type and cause of a lesion. Analysis of mucosal blood flow
Blood flow
Blood flow is the continuous running of blood in the cardiovascular system.The human body is made up of several processes all carrying out various functions. We have the gastrointestinal system which aids the digestion and the absorption of food...
in the oral cavity in combination with the assessment of autonomous cardiovascular factors appears to be useful in the diagnosis of autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
disorders in burning mouth syndrome and in patients with inborn disorders, both of which are associated with gustatory dysfunction. Cell cultures may also be used when fungal or bacterial infections are suspected.
In addition, the analysis of saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
should be performed, as it constitutes the environment of taste receptors
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
, including transport of tastes to the receptor and protection of the taste receptor. Typical clinical investigations involve sialometry and sialochemistry. Studies have shown that electron micrographs
Micrograph
A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an item.Micrographs are widely used in all fields of microscopy.-Photomicrograph:...
of taste receptors obtained from saliva samples indicate pathological changes in the taste buds of patients with dysgeusia and other gustatory disorders.
Chemotherapy
A major cause of dysgeusia is antineoplastic chemotherapyChemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
. Chemotherapy often induces damage to the oral cavity, resulting in oral mucositis, oral infection, and salivary gland dysfunction. Oral mucositis consists of inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
of the mouth, along with sores and ulcers
Mouth ulcer
A mouth or oral ulcer is an open sore in the mouth, or rarely a break in the mucous membrane or the epithelium on the lips or surrounding the mouth. The types of mouth ulcers are diverse, with a multitude of associated causes including: physical abrasion, acidic fruit, infection, other medical...
in the tissues. Healthy individuals normally have a diverse range of microbial organisms residing in their oral cavities; however, chemotherapy can permit these typically non-pathogenic agents to cause serious infection, which may result in a decrease in saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
. In addition, patients who undergo radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
also lose salivary tissues. Saliva is an important component of the taste mechanism. Saliva both interacts with and protects the taste receptors in the mouth. Saliva mediates sour and sweet tastes through bicarbonate ions and glutamate, respectively. The salt taste is induced when sodium chloride levels surpass the concentration in the saliva. It has been reported that 50% of chemotherapy patients have suffered from either dysgeusia or another form of taste impairment. Examples of chemotherapy treatments that can lead to dysgeusia are cyclophosphamide
Cyclophosphamide
Cyclophosphamide , also known as cytophosphane, is a nitrogen mustard alkylating agent, from the oxazophorines group....
, cisplatin
Cisplatin
Cisplatin, cisplatinum, or cis-diamminedichloroplatinum is a chemotherapy drug. It is used to treat various types of cancers, including sarcomas, some carcinomas , lymphomas, and germ cell tumors...
, and etoposide
Etoposide
Etoposide phosphate is an anti-cancer agent. It is known in the laboratory as a topoisomerase poison. Etoposide is often incorrectly referred to as a topoisomerase inhibitor in order to avoid using the term "poison" in a clinical setting...
. The exact mechanism of chemotherapy-induced dysgeusia is unknown.
Taste buds
Distortions in the taste buds may give rise to dysgeusia. In one study conducted by Masahide Yasuda and Hitoshi Tomita from Nihon University of Japan, it has been observed that patients suffering from this taste disorder have less microvilli than normal. In addition, the nucleusCell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
and cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
of the taste bud cells have been reduced. Based on their findings, dygeusia results from loss of microvilli and the reduction of Type III intracellular vesicles, all of which could potentially interfere with the gustatory pathway.
Zinc deficiency
Another primary cause of dysgeusia is zincZinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
deficiency. While the exact role of zinc in dysgeusia is unknown, it has been cited that zinc is partly responsible for the repair and production of taste buds. Zinc somehow directly or indirectly interacts with carbonic anhydrase VI, influencing the concentration of gustin, which is linked to the production of taste buds. It has also been reported that patients treated with zinc experience an elevation in calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
concentration in the saliva. In order to work properly, taste buds rely on calcium receptors. Zinc “is an important cofactor for alkaline phosphatase
Alkaline phosphatase
Alkaline phosphatase is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation...
, the most abundant enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
in taste bud membranes; it is also a component of a parotid salivary protein important to the development and maintenance of normal taste buds.”
Drugs
There are also a wide variety of drugs that can trigger dysgeusia, including H1-antihistamines, such as azelastineAzelastine
Azelastine is a potent, second-generation, selective, histamine antagonist manufactured by MedaPharma. According to the Allergic Rhinitis and its Impact on Asthma treatment guidelines, intranasal anti-histamines are recommended for the first line therapy of mild intermittent, moderate/severe...
and emedastine
Emedastine
Emedastine difumarate is an second generation antihistamine used in eye drops to treat allergic conjunctivitis. It's mechanism of action is a H1 receptor antagonist....
. Approximately 250 drugs affect taste. The sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
channels linked to taste receptors can be inhibited by amiloride
Amiloride
Amiloride is a potassium-sparing diuretic, first approved for use in 1967 , used in the management of hypertension and congestive heart failure. Amiloride was also tested as treatment of cystic fibrosis, but it was revealed inefficient in vivo due to it's short time of action, therefore...
, and the creation of new taste buds and saliva can be impeded by antiproliferative drugs. Saliva can have traces of the drug, giving rise to a metallic flavor in the mouth; examples include lithium carbonate
Lithium carbonate
Lithium carbonate is a chemical compound of lithium, carbon, and oxygen with the formula Li2CO3. This colorless salt is widely used in the processing of metal oxides and has received attention for its use in psychiatry. It is found in nature as the rare mineral zabuyelite.-Properties:Like almost...
and tetracyclines. Drugs containing sulfhydryl groups, including penicillamine
Penicillamine
Penicillamine is a pharmaceutical of the chelator class. It is sold under the trade names of Cuprimine and Depen. The pharmaceutical form is D-penicillamine, as L-penicillamine is toxic...
and captopril
Captopril
Captopril is an angiotensin-converting enzyme inhibitor used for the treatment of hypertension and some types of congestive heart failure. Captopril was the first ACE inhibitor developed and was considered a breakthrough both because of its novel mechanism of action and also because of the...
, may react with zinc and cause deficiency. Metronidazole
Metronidazole
Metronidazole is a nitroimidazole antibiotic medication used particularly for anaerobic bacteria and protozoa. Metronidazole is an antibiotic, amebicide, and antiprotozoal....
and chlorhexidine have been found to interact with metal ions that associate with the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
.
Drugs that prevent the production of angiotensin II by inhibiting angiotensin converting enzyme, eprosartan
Eprosartan
Eprosartan is an angiotensin II receptor antagonist used for the treatment of high blood pressure. It is marketed as Teveten by Abbott Laboratories in the United States.It is marketed as Eprozar by INTAS Pharmaceuticals in the INDIA and by Solvay Pharmaceuticals elsewhere...
for example, have been linked to dysgeusia.
Miscellaneous causes
XerostomiaXerostomia
Xerostomia is the medical term for the subjective complaint of dry mouth due to a lack of saliva. Xerostomia is sometimes colloquially called pasties, cottonmouth, drooth, or doughmouth. Several diseases, treatments, and medications can cause xerostomia. It can also be exacerbated by smoking or...
, also known as dry mouth syndrome, can precipitate dysgeusia because normal salivary flow and concentration are necessary for taste. Injury to the glossopharyngeal nerve
Glossopharyngeal nerve
The glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
can result in dysgeusia. In addition, damage done to the pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
, thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
, and midbrain, all of which compose the gustatory pathway, can be potential factors. In a case study, 22% of patients who were experiencing a bladder obstruction were also suffering from dysgeusia. Dysgeusia was eliminated in 100% of these patients once the obstruction was removed. Although it is uncertain what the relationship between bladder relief and dysgeusia entails, it has been observed that the areas responsible for urinary system
Urinary system
The urinary system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder and the urethra.-Kidney:...
and taste in the pons and cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
in the brain are close in proximity.
Many of the causes for dysgeusia are not fully understood, making idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
dysgeusia very common. A wide range of miscellaneous factors may contribute to this taste disorder, such as gastric reflux, lead poisoning
Lead poisoning
Lead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems...
, and diabetes mellitus
Diabetes mellitus
Diabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
. A minority of pine nut
Pine nut
Pine nuts are the edible seeds of pines . About 20 species of pine produce seeds large enough to be worth harvesting; in other pines the seeds are also edible, but are too small to be of great value as a human food....
s can apparently cause taste disturbances, for reasons which are not entirely proven. Certain pesticides can have damaging effects on the taste buds and nerves in the mouth. These pesticides include organochloride
Organochloride
An organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
compounds and carbamate
Carbamate
Carbamates are organic compounds derived from carbamic acid . A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally and often are interconverted chemically. Carbamate esters are also called urethanes.-Synthesis:Carbamic acids are derived...
pesticides. Damage to the peripheral nerves, along with injury to the chorda tympani
Chorda tympani
The chorda tympani is a nerve that branches from the facial nerve inside the facial canal, just before the facial nerve exits the skull via the Stylomastoid foramen...
branch of the facial nerve, also cause dysgeusia. A surgical risk for laryngoscopy
Laryngoscopy
Laryngoscopy is a medical procedure that is used to obtain a view of the vocal folds and the glottis. Laryngoscopy may be performed to facilitate tracheal intubation during general anesthesia or cardiopulmonary resuscitation or for procedures on the larynx or other parts of the upper...
and tonsillectomy
Tonsillectomy
A tonsillectomy is a 3,000-year-old surgical procedure in which the tonsils are removed from either side of the throat. The procedure is performed in response to cases of repeated occurrence of acute tonsillitis or adenoiditis, obstructive sleep apnea, nasal airway obstruction, snoring, or...
include dysgeusia. Patients who suffer from the burning mouth syndrome, most likely menopausal women, are often suffering from dysgeusia as well.
Artificial saliva and pilocarpine
Because medications have been linked to approximately 22% to 28% of all cases of dysgeusia, researching a treatment for this particular cause has been important. XerostomiaXerostomia
Xerostomia is the medical term for the subjective complaint of dry mouth due to a lack of saliva. Xerostomia is sometimes colloquially called pasties, cottonmouth, drooth, or doughmouth. Several diseases, treatments, and medications can cause xerostomia. It can also be exacerbated by smoking or...
, or a decrease in saliva flow, can be a side effect of many drugs, which, in turn, can lead to the development of taste disturbances such as dysgeusia. Patients can lessen the effects of xerostomia with breath mints, sugarless gum, or lozenges, or physicians can increase saliva flow with artificial saliva or oral pilocarpine
Pilocarpine
Pilocarpine is a parasympathomimetic alkaloid obtained from the leaves of tropical American shrubs from the genus Pilocarpus. It is a non-selective muscarinic receptor agonist in the parasympathetic nervous system, which acts therapeutically at the muscarinic acetylcholine receptor M3 due to its...
. Artificial saliva mimics the characteristics of natural saliva by lubricating and protecting the mouth but does not provide any digestive or enzymatic benefits. Pilocarpine is a cholinergic
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
drug meaning it has the same effects as the neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
. Acetylcholine has the function of stimulating the salivary glands to actively produce saliva. The increase in saliva flow is effective in improving the movement of tastants to the taste buds.
Zinc supplementation
Approximately one half of drug-related taste distortions are caused by a zinc deficiencyZinc deficiency
Zinc deficiency is insufficient zinc to meet the needs of biological organisms. It can occur in both plants and animals. Zinc deficient soil is soil in which there is insufficient zinc to allow plants to grow normally.-Description:...
. Many medications are known to chelate, or bind, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
preventing the element from functioning properly. Due to the causal relationship of insufficient zinc levels to taste disorders, research has been conducted to test the efficacy of zinc supplementation as a possible treatment for dygeusia. In a randomized clinical trial, fifty patients suffering from idiopathic
Idiopathic
Idiopathic is an adjective used primarily in medicine meaning arising spontaneously or from an obscure or unknown cause. From Greek ἴδιος, idios + πάθος, pathos , it means approximately "a disease of its own kind". It is technically a term from nosology, the classification of disease...
dysgeusia were given either zinc or a lactose placebo
Placebo
A placebo is a simulated or otherwise medically ineffectual treatment for a disease or other medical condition intended to deceive the recipient...
. The patients prescribed the zinc reported experiencing improved taste function and less severe symptoms compared to the control group, suggesting that zinc may be a beneficial treatment. The efficacy of zinc, however, has been ambiguous in the past. In a second study, 94% of patients who were provided with zinc supplementation did not experience any improvement in their condition. This ambiguity is most likely due to small sample sizes and the wide range of causes of dysgeusia. A recommended daily oral dose of 25–100 mg appears to be an effective treatment for taste dysfunction provided that there are low levels of zinc in the blood serum
Blood serum
In blood, the serum is the component that is neither a blood cell nor a clotting factor; it is the blood plasma with the fibrinogens removed...
. There is not a sufficient amount of evidence to determine whether or not zinc supplementation is able to treat dysgeusia when low zinc concentrations are not detected in the blood.
Zinc infusion in chemotherapy
It has been reported that approximately 68% of cancer patients undergoing chemotherapyChemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
experience disturbances in sensory perception such as dysgeusia. In a pilot study involving twelve lung cancer patients, chemotherapy drugs were infused with zinc in order to test its potential as a treatment. The results indicated that, after two weeks, no taste disturbances were reported by the patients who received the zinc-supplemented treatment while most of the patients in the control group who did not receive the zinc reported taste alterations. A multi-institutional study involving a larger sample size of 169 patients, however, indicated that zinc-infused chemotherapy did not have an effect on the development of taste disorders in cancer patients. An excess amount of zinc in the body can have negative effects on the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, and physicians must use caution when administering zinc to immunocompromised cancer patients. Because taste disorders can have detrimental effects on a patient's quality of life, more research needs to be conducted concerning possible treatments such as zinc supplementation.
Altering drug therapy
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
was being treated with valsartan
Valsartan
Valsartan is an angiotensin II receptor antagonist , with particularly high affinity for the type I angiotensin receptor. By blocking the action of angiotensin, valsartan dilates blood vessels and reduces blood pressure...
. Due to this drug's inability to treat her condition, she began taking a regimen of eprosartan
Eprosartan
Eprosartan is an angiotensin II receptor antagonist used for the treatment of high blood pressure. It is marketed as Teveten by Abbott Laboratories in the United States.It is marketed as Eprozar by INTAS Pharmaceuticals in the INDIA and by Solvay Pharmaceuticals elsewhere...
, an angiotensin II receptor antagonist
Angiotensin II receptor antagonist
Angiotensin II receptor antagonists, also known as angiotensin receptor blockers , AT1-receptor antagonists or sartans, are a group of pharmaceuticals which modulate the renin-angiotensin-aldosterone system...
. Within three weeks, she began experiencing a metallic taste and a burning sensation in her mouth that ceased when she stopped taking the medication. When she began taking eprosartan on a second occasion, her dysgeusia returned. In a second case, a fifty-nine-year-old man was prescribed amlodipine
Amlodipine
Amlodipine is a long-acting calcium channel blocker used as an anti-hypertensive and in the treatment of angina...
in order to treat his hypertension. After eight years of taking the drug, he developed a loss of taste sensation and numbness in his tongue. When he ran out of his medication, he decided not to obtain a refill and stopped taking amlodipine. Following this self-removal, he reported experiencing a return of his taste sensation. Once he refilled his prescription and began taking amlodipine a second time, his taste disturbance reoccurred. These two cases suggest that there is an association between these drugs and taste disorders. This link is supported by the "de-challenge" and "re-challenge" that took place in both instances. It appears that drug-induced dysgeusia can be alleviated by reducing the drug's dose or by substituting a second drug from the same class.
Alpha lipoic acid
Alpha lipoic acid (ALA) is an antioxidantAntioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
that is made naturally by human cells. It can also be administered in capsules or can be found in foods such as red meat, organ meats, and yeast. Like other antioxidants, it functions by ridding the body of harmful free radicals that can cause damage to tissues and organs. It has an important role in the Krebs cycle as a coenzyme leading to the production of antioxidants, intracellular glutathione
Glutathione
Glutathione is a tripeptide that contains an unusual peptide linkage between the amine group of cysteine and the carboxyl group of the glutamate side-chain...
, and nerve-growth factors. Animal research has also uncovered the ability of ALA to improve nerve conduction velocity
Nerve conduction velocity
Nerve conduction velocity is the speed at which an electrochemical signal propagates down a neural pathway. Many things can affect this, including axon diameter, myelination, the internal resistance of the axon, and temperature. Nerve conduction velocity differs from species to species, and to a...
. Because flavors are perceived by differences in electric potential
Electric potential
In classical electromagnetism, the electric potential at a point within a defined space is equal to the electric potential energy at that location divided by the charge there...
through specific nerves innervating the tongue, idiopathic dysgeusia may be a form of a neuropathy. ALA has proven to be an effective treatment for burning mouth syndrome spurring studies in its potential to treat dysgeusia. In a study of forty-four patients diagnosed with the disorder, one half was treated with the drug for two months while the other half, the control group, was given a placebo for two months followed by a two month treatment of ALA. The results reported show that 91% of the group initially treated with ALA reported an improvement in their condition compared to only 36% of the control group. After the control group was treated with ALA, 72% reported an improvement. This study suggests that ALA may be a potential treatment for patients and supports that full double blind randomized studies should be performed.
Managing dysgeusia
In addition to the aforementioned treatments, there are also many management approaches that can alleviate the symptoms of dysgeusia. These include using non-metallic silverware, avoiding metallic or bitter tasting foods, increasing the consumption of foods high in protein, flavoring foods with spices and seasonings, serving foods cold in order to reduce any unpleasant taste or odor, frequently brushing one's teeth and utilizing mouthwash, or using sialogogues such as chewing sugar-free gum or sour-tasting drops that stimulate the productivity of saliva. When taste is impeded, the food experience can be improved through means other than taste, such as texture, aroma, temperature, and color.Psychological impacts
People who suffer from dysgeusia are also forced to manage the impact that the disorder has on their quality of life. An altered taste has effects on food choice and intake and can lead to weight lossWeight loss
Weight loss, in the context of medicine, health or physical fitness, is a reduction of the total body mass, due to a mean loss of fluid, body fat or adipose tissue and/or lean mass, namely bone mineral deposits, muscle, tendon and other connective tissue...
, malnutrition
Malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....
, impaired immunity, and a decline in health. Patients diagnosed with dysgeusia must use caution when adding sugar and salt to food and must be sure not to over compensate for their lack of taste with excess amounts. Since the elderly are often on multiple medications, they are at risk for taste disturbances increasing the chances of developing depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...
, loss of appetite, and extreme weight loss. This is cause for an evaluation and management of their dysgeusia. In patients undergoing chemotherapy, taste distortions can often be severe and make compliance with cancer treatment difficult. Other problems that may arise include anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
and behavioral changes that can be misinterpreted as psychiatric delusions regarding food. Symptoms including paranoia
Paranoia
Paranoia [] is a thought process believed to be heavily influenced by anxiety or fear, often to the point of irrationality and delusion. Paranoid thinking typically includes persecutory beliefs, or beliefs of conspiracy concerning a perceived threat towards oneself...
, amnesia
Amnesia
Amnesia is a condition in which one's memory is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia...
, cerebellar malfunction, and lethargy can also manifest when undergoing histidine
Histidine
Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...
treatment. This makes it critical that these patients' dysgeusia is either treated or managed in order to improve their quality of life.
Future research
Every year, more than 200,000 individuals see their physicians concerning chemosensory problems, and many more taste disturbances are never reported. Due to the large number of persons affected by taste disorders, basic and clinical research are receiving support at different institutions and chemosensory research centers across the country. These taste and smell clinics are focusing their research on better understanding the mechanisms involved in gustatory function and taste disorders such as dysgeusia. For example, the National Institute on Deafness and Other Communication DisordersNational Institute on Deafness and Other Communication Disorders
The National Institute on Deafness and Other Communication Disorders , a member of the U.S. National Institutes of Health, is mandated to conduct and support biomedical and behavioral research and research training in the normal and disordered processes of hearing, balance, smell, taste, voice,...
is looking into the mechanisms underlying the key receptors on taste cells and applying this knowledge to the future of medications and artificial food products. Meanwhile, the Taste and Smell Clinic at the University of Connecticut Health Center
University of Connecticut Health Center
The University of Connecticut Health Center includes the , School of Dental Medicine, , the UConn Medical Group, UConn Health Partners and . Founded in 1961, the Health Center pursues a mission of providing outstanding health care education in an environment of exemplary patient care, research and...
is integrating behavioral, neurophysiological, and genetic studies involving stimulus concentrations and intensities in order to better understand taste function. The purpose of these studies is to unearth the biological mechanisms underlying taste and to use this data to eliminate taste disorders in order to improve the lives of taste disorder sufferers.