Silent stroke
Encyclopedia
A silent stroke is a stroke
that does not have any outward symptoms, and the patient is typically unaware they have suffered a stroke. Despite not causing identifiable symptoms a silent stroke still causes damage to the brain, and places the patient at increased risk for both transient ischemic attack
and major stroke in the future. In a broad study in 1998, more than 11 million people were estimated to have experienced a stroke in the United States. Approximately 770,000 of these strokes were symptomatic and 11 million were first-ever silent MRI infarcts or hemorrhages. Silent strokes typically cause lesion
s which are detected via the use of neuroimaging such as MRI. The risk of silent stroke increases with age but may also affect younger adults. Women appear to be at increased risk for silent stroke, with hypertension
and current cigarette smoking being amongst the predisposing factors.
These type of strokes include lacunar and other ischemic strokes and minor hemorrhages, they may also include leukoaraiosis
(changes in the white matter
of the brain), the white matter is more susceptible to vascular blockage due to reduced amount of blood vessels as compared to the cerebral cortex
. These strokes are termed "silent" because they typically affect "silent" regions of the brain that do not cause a noticeable change in an afflicted person’s motor functions such as contralateral paralysis, slurred speech
, pain, or an alteration in the sense of touch. A silent stroke typically affects regions of the brain associated with various thought processes, mood regulation and cognitive functions and is a leading cause of vascular cognitive impairment
and may also lead to a loss of urinary bladder
control.
In the Cardiovascular Health Study, a population study conducted among 3,660 adults over the age of 65, 31% showed evidence of silent stroke in neuroimaging studies utilizing MRI. These individuals were unaware they had suffered a stroke. It is estimated that silent strokes are five times more prevalent than symptomatic stroke.
A silent stroke differs from a transient ischemic attack (TIA). In TIA symptoms of stroke are exhibited which may last from a few minutes to 24 hours before resolving. A TIA is a risk factor for having a major stroke and subsequent silent strokes in the future.
Preventive measures that can be taken to avoid sustaining a silent stroke for the general public are the same as for stroke. Smoking cessation
is the most immediate step that can be taken with the effective management of hypertension the major medically treatable factor.
ultrasonography (TCD), which measures cerebral blood flow velocity (CBFV) in the large intracranial arteries in the brain, has been shown in various studies to be an effective tool to diagnose those at increased risk of having an initial or recurrent silent stroke. The narrowing of these arteries which is a risk factor for cerebral infarction, is characterized by an increased velocity of blood flow. Transfusion therapy
lowers the risk for a new silent stroke in children have both abnormal TCD ultrasonographic velocity and previous silent infarct even when the initial MRI showed no abnormality. A finding of elevated TCD ultrasonographic velocity warrants MRI of the brain as those with both abnormalities who are not provided transfusion therapy are at higher risk for developing a new silent infarct or stroke than are those whose initial MRI showed no abnormality. In children with elevated TCD ultrasonographic velocity an additional MRI of the brain is warranted despite the initial normal findings.
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
that does not have any outward symptoms, and the patient is typically unaware they have suffered a stroke. Despite not causing identifiable symptoms a silent stroke still causes damage to the brain, and places the patient at increased risk for both transient ischemic attack
Transient ischemic attack
A transient ischemic attack is a transient episode of neurologic dysfunction caused by ischemia – either focal brain, spinal cord or retinal – without acute infarction...
and major stroke in the future. In a broad study in 1998, more than 11 million people were estimated to have experienced a stroke in the United States. Approximately 770,000 of these strokes were symptomatic and 11 million were first-ever silent MRI infarcts or hemorrhages. Silent strokes typically cause lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s which are detected via the use of neuroimaging such as MRI. The risk of silent stroke increases with age but may also affect younger adults. Women appear to be at increased risk for silent stroke, with hypertension
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...
and current cigarette smoking being amongst the predisposing factors.
These type of strokes include lacunar and other ischemic strokes and minor hemorrhages, they may also include leukoaraiosis
Leukoaraiosis
Leukoaraiosis or periventricular white matter disease is a term for changes in the cerebral white matter that can be detected with high frequency by CT and MRI in aged individuals. It is a descriptive term for rarefaction of the white matter. It is also commonly referred to as white matter...
(changes in the white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
of the brain), the white matter is more susceptible to vascular blockage due to reduced amount of blood vessels as compared to the 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...
. These strokes are termed "silent" because they typically affect "silent" regions of the brain that do not cause a noticeable change in an afflicted person’s motor functions such as contralateral paralysis, slurred speech
Dysarthria
Dysarthria is a motor speech disorder resulting from neurological injury of the motor component of the motor-speech system and is characterized by poor articulation of phonemes...
, pain, or an alteration in the sense of touch. A silent stroke typically affects regions of the brain associated with various thought processes, mood regulation and cognitive functions and is a leading cause of vascular cognitive impairment
Vascular cognitive impairment
Vascular cognitive impairment is a term used to describe a spectrum of cognitive impairments caused by various types of cerebrovascular disease that occurs as a result of interaction between a variety of vascular risk factors such as hypertension, obesity, dyslipidemia, diabetes mellitus, stroke...
and may also lead to a loss of urinary bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
control.
In the Cardiovascular Health Study, a population study conducted among 3,660 adults over the age of 65, 31% showed evidence of silent stroke in neuroimaging studies utilizing MRI. These individuals were unaware they had suffered a stroke. It is estimated that silent strokes are five times more prevalent than symptomatic stroke.
A silent stroke differs from a transient ischemic attack (TIA). In TIA symptoms of stroke are exhibited which may last from a few minutes to 24 hours before resolving. A TIA is a risk factor for having a major stroke and subsequent silent strokes in the future.
Types of Silent Stroke
- Ischemic stroke: occurs when a blood vessel supplying blood to the brain becomes blocked. This type of stroke accounts for approximately 87 percent of all stroke cases.
- Hemorrhagic stroke: occurs when a blood vessel supplying blood to the brain becomes weakened and ruptures. Typically hemorrhagic stroke is caused by two types of weakened blood vessel: aneurysmAneurysmAn aneurysm or aneurism is a localized, blood-filled balloon-like bulge in the wall of a blood vessel. Aneurysms can commonly occur in arteries at the base of the brain and an aortic aneurysm occurs in the main artery carrying blood from the left ventricle of the heart...
s and arteriovenous malformationArteriovenous malformationArteriovenous malformation or AVM is an abnormal connection between veins and arteries, usually congenital. This pathology is widely known because of its occurrence in the central nervous system, but can appear in any location. An arteriovenous malformation is a vascular anomaly. It is a...
s (AVMs). - Lacunar infarctsLacunar strokeLacunar stroke or lacunar infarct is a type of stroke that results from occlusion of one of the penetrating arteries that provides blood to the brain's deep structures...
(LACI) are small (0.2 to 15 mm in diameter) noncortical (does not affect cerebral cortexCerebral cortexThe 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...
) infarcts caused by the occlusion of a single penetrating branch of a larger blood vessel that provides blood to the brain's deep structures including the white matter. LACIs are strongly associated with the development of white matter lesions (WML) which can be detected via the use of computerized tomography (CT scans).
Risk factors
There are various individual risk factors associated with having a silent stroke. Many of these risk factors are the same as those associated with having a major symptomatic stroke.- AcroleinAcroleinAcrolein is the simplest unsaturated aldehyde. It is produced widely but is most often immediately reacted with other products due to its instability and toxicity...
:elevated levels of acrolein, a toxic metaboliteMetaboliteMetabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
produced from the polyamines spermineSpermineSpermine is a polyamine involved in cellular metabolism found in all eukaryotic cells. Formed from spermidine, it is found in a wide variety of organisms and tissues and is an essential growth factor in some bacteria. It is found as a polycation at physiological pH...
, spermidineSpermidineSpermidine is a polyamine involved in cellular metabolism. Its known actions include:#Inhibition of neuronal nitric oxide synthase, nNOS#Assisting the in vitro process of transcribing RNA via stimulation of T4 polynucleotide kinase and T7 RNA polymerase activity; it binds to and precipitates DNA...
and by amine oxidaseAmine oxidaseAmine oxidase is an enzyme involved in the metabolism of histamine.-External links:...
serve as a marker for silent stroke, when elevated in conjunction with C-reactive protein and interleukin 6 the confidence levels in predicting a silent stroke risk increase. - AdiponectinAdiponectinAdiponectin is a protein which in humans is encoded by the ADIPOQ gene.- Structure :...
: is a type of protein secreted by adipose cells that improves insulin sensitivity and possesses antiatherogenicAtherosclerosisAtherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...
properties. Lower levels of s-adiponectin are associated with ischemic stroke. - Aging: the prevalence of silent stroke rises with increasing age with a prevalence rate of over twenty percent of the elderly increasing to 30%-40% in those over the age of 70.
- AnemiaAnemiaAnemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
: children with acute anemia caused by medical conditions other than sickle cell anemia with hemoglobin below 5.5 gGramThe gram is a metric system unit of mass....
/dL. are at increased risk for having a silent stroke according to a study released at American Stroke Association's International Stroke Conference 2011. The researchers suggested a thorough examination for evidence of silent stroke in all severely anemic children in order to facilitate timely intervention to ameliorate the potential brain damage.- Sickle cell anemia: is an autosomal recessive genetic blood disorder caused in the gene (HBB gene) which codes for hemoglobin (Hg) and results in lowered levels. The blood cells in sickle cell disease are abnormally shaped (sickle-shaped) and may form clots or block blood vessels. Estimates of children with sickle cell anemia who suffer strokes (with silent strokes predominating in the younger patients) range from 15%-30%. These children are at significant risk of cognitive impairment and poor educational outcomes.
- Thalassemia major: is an autosomal recessive genetically inherited form of hemolytic anemia, characterized by red blood cell (hemoglobin) production abnormalities. Children with this disorder are at increased risk for silent stroke.
- Atrial fibrillationAtrial fibrillationAtrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
(AF): atrial fibrillation (irregular heartbeat) is associated with an increased risk for silent stroke. - Cigarette smoking: The procoagulant and atherogenic effects of smoking increase the risk for silent stroke. Smoking also has a deleterious effect on regional cerebral blood flowCerebral blood flowCerebral blood flow, or CBF, is the blood supply to the brain in a given time. In an adult, CBF is typically 750 millitres per minute or 15% of the cardiac output. This equates to 50 to 54 millilitres of blood per 100 grams of brain tissue per minute. CBF is tightly regulated to meet the brain's...
(rCBF). The chances of having a stroke increase with the amount of cigarettes smoked and the length of time an individual has smoked (pack years). - C-reactive proteinC-reactive proteinC-reactive protein is a protein found in the blood, the levels of which rise in response to inflammation...
(CRP) and Interleukin 6Interleukin 6Interleukin-6 is a protein that in humans is encoded by the IL6 gene.IL-6 is an interleukin that acts as both a pro-inflammatory and anti-inflammatory cytokine. It is secreted by T cells and macrophages to stimulate immune response, e.g. during infection and after trauma, especially burns or other...
(IL6): C-reactive protein is one of the plasma proteins known as acute phase proteinAcute phase proteinAcute-phase proteins are a class of proteins whose plasma concentrations increase or decrease in response to inflammation...
s (proteins whose plasmaBlood plasmaBlood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
concentrations increase (or decrease) by 25% or more during inflammatory disorders) which is produced by the liver. The level of CRP rises in response to inflammation in various parts of the body including vascular inflammation. The level of CRP can rise as high as 1000-fold in response to inflammation. Other conditions that can cause marked changes in CRP levels include infection, trauma, surgery, burns, inflammatory conditions, and advanced cancer. Moderate changes can also occur after strenuous exercise, heatstroke, and childbirth. Increased levels of CRP as measured by a CRP test or the more sensitive high serum CRP (hsCRP) test have a close correlation to inceased risk of silent stroke. Interleukin-6 is an interleukinInterleukinInterleukins are a group of cytokines that were first seen to be expressed by white blood cells . The term interleukin derives from "as a means of communication", and "deriving from the fact that many of these proteins are produced by leukocytes and act on leukocytes"...
(type of protein) produced by T-cells (specialized white blood cells), macrophages and endothelial cells. IL6 is also classified as a cytokineCytokineCytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
(acts in relaying information between cells). IL6 is involved in the regulation of the acute phase response to injury and infection may act as both an anti-inflammatory agent and a pro-inflammatory.Increased levels of CRP as measured by a CRP test or the more sensitive high serum CRP (hsCRP) test and elevated levels of I6 as measured by an IL6 ELISAELISAEnzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
are markers for the increased risk of silent stroke. - Diabetes mellitusDiabetes mellitusDiabetes 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...
:untreated or improperly managed diabetes mellitus ias associated with increased an increased risk for silent stroke. - HypertensionHypertensionHypertension 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...
: which affects up to 50 million people in the United States alone is the major treatable risk factor associated with silent stokes. - HomocysteineHomocysteineHomocysteine is a non-protein amino acid with the formula HSCH2CH2CHCO2H. It is a homologue of the amino acid cysteine, differing by an additional methylene group. It is biosynthesized from methionine by the removal of its terminal Cε methyl group...
: elevated levels of total homocysteine (tHcy) an amino acidAmino acidAmino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
are an independent risk factor for silent stroke, even in healthy middle-aged adults. - Metabolic syndromeMetabolic syndromeMetabolic syndrome is a combination of medical disorders that, when occurring together, increase the risk of developing cardiovascular disease and diabetes. It affects one in five people in the United States and prevalence increases with age...
(MetS):Metabolic syndrome is a name for a group of risk factors that occur together and increase the risk for coronary artery disease, stroke, and type 2 diabetes. A higher number of these MetS risk factors the greater the chance of having a silent sroke.- Polycystic ovary syndromePolycystic ovary syndromePolycystic ovary syndrome is one of the most common female endocrine disorders. PCOS is a complex, heterogeneous disorder of uncertain aetiology, but there is strong evidence that it can to a large degree be classified as a genetic disease....
(PCOS): is associated with double the risk for arterial disease including silent stroke independent of the subjects Body mass indexBody mass indexThe body mass index , or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was invented between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing...
(BMI).
- Polycystic ovary syndrome
Neuropsychological deficits
Individuals with have had silent strokes often have various neuropsychological deficits and have significant impairment in multiple areas of cognitive performance.In children
Children who have suffered silent strokes often have a variety of neuropsychological deficits, these deficits may include lowered I.Q., learning disbilities and an inability to focus.Link to depression
Major depression is a risk factor and also a consequence of SBI. Persons who present with symptoms os presenile and senile major depression showed a markedly higher incidence of SBI (65.9% and 93.7%). Individuals with major depression who have had an SBI present with more marked neurological defits and more severe depressive symptoms than do those without SBI.Diagnosis
The diagnosis of a silent stroke is usually made as an incidental (by chance) finding of various neuroimaging techniques. Silent strokes may be detected by:- Magnetic resonance imagingMagnetic resonance imagingMagnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) - Computerized axial tomography (CAT scan)
Prevention
See main article:Stroke preventionPreventive measures that can be taken to avoid sustaining a silent stroke for the general public are the same as for stroke. Smoking cessation
Smoking cessation
Smoking cessation is the process of discontinuing the practice of inhaling a smoked substance. This article focuses exclusively on cessation of tobacco smoking; however, the methods described may apply to cessation of smoking other substances that can be difficult to stop using due to the...
is the most immediate step that can be taken with the effective management of hypertension the major medically treatable factor.
In Children with Sickle cell anemia
In children with sickle cell anemia Transcranial DopplerTranscranial doppler
Transcranial Doppler is a test that measures the velocity of blood flow through the brain's blood vessels. Used to help in the diagnosis of emboli, stenosis, vasospasm from a subarachnoid hemorrhage , and other problems, this relatively quick and inexpensive test is growing in popularity in the...
ultrasonography (TCD), which measures cerebral blood flow velocity (CBFV) in the large intracranial arteries in the brain, has been shown in various studies to be an effective tool to diagnose those at increased risk of having an initial or recurrent silent stroke. The narrowing of these arteries which is a risk factor for cerebral infarction, is characterized by an increased velocity of blood flow. Transfusion therapy
Transfusion therapy (Sickle-cell disease)
Transfusion therapy for sickle-cell disease entails the use of blood tranfusions in the management of acute cases of sickle cell disease and as a prophylaxis to prevent complications by decreasing the number of red blood cells that can sickle by adding normal red blood cells...
lowers the risk for a new silent stroke in children have both abnormal TCD ultrasonographic velocity and previous silent infarct even when the initial MRI showed no abnormality. A finding of elevated TCD ultrasonographic velocity warrants MRI of the brain as those with both abnormalities who are not provided transfusion therapy are at higher risk for developing a new silent infarct or stroke than are those whose initial MRI showed no abnormality. In children with elevated TCD ultrasonographic velocity an additional MRI of the brain is warranted despite the initial normal findings.
See also
- StrokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
- HypertensionHypertensionHypertension 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...
- Cerebral hypoxiaCerebral hypoxiaCerebral hypoxia refers to a reduced supply of oxygen to the brain. Cerebral anoxia refers to a complete lack of oxygen to the brain. There are four separate categories of cerebral hypoxia; in order of severity they are; diffuse cerebral hypoxia , focal cerebral ischemia, cerebral infarction, and...
- DASH diet (Dietary Approaches to Stop Hypertension)
External links
- Stanford Stroke Risk Assessment Test http://strokecenter.stanford.edu/test.html
- Acute anemia linked to silent strokes in children http://www.newsroom.heart.org/index.php?s=43&item=1260
- Guidelines for the Primary Prevention of Stroke A Guideline for Healthcare Professionals From the American Heart Association/American Stroke Association http://stroke.ahajournals.org/cgi/content/full/42/2/517
- Risk of “silent stroke” in patients older than 60 years: risk assessment and clinical perspectives:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2938031/?tool=pubmed