Normal pressure hydrocephalus
Encyclopedia
Normal pressure hydrocephalus (NPH), also termed symptomatic hydrocephalus, occurs when there is an increase in intracranial pressure
(ICP) due to an abnormal accumulation of cerebrospinal fluid
(CSF) in the ventricles of the brain, which can cause ventriculomegaly
. The ICP gradually falls but still maintains a slightly elevated level and the CSF pressure reaches a high normal level of 150 to 200 mmH2O. Measurements of ICP, therefore, are not usually elevated. Because of this equilibration, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness. (Though some studies have shown pressure elevations to occur only intermittently). However, the enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient. The classic triad of gait disturbance, urinary incontinence, and dementia
or mental decline, was first described by Hakim and Adams in 1965. NPH is often misdiagnosed as Parkinson's disease
, Alzheimer's disease
, or dementia
, due to its chronic nature and nonspecfic presenting symptoms [see below]. Although the exact mechanism is unknown, normal-pressure hydrocephalus is thought to be a form of communicating hydrocephalus with impaired CSF reabsorption at the arachnoid granulations.
There are 2 types of normal pressure hydrocephalus: idiopathic and secondary. The term idiopathic means that it has no known cause. The secondary type of NPH can be due to a subarachnoid haemorrhage, head trauma, tumour, CNS infection, or a complication of cranial surgery.
Recent population-based studies have estimated the prevalence of NPH to be about 0.5% in those over 65 years old, with an incidence of about 5.5 patients per 100,000 of people per year. This is in accordance with comparable findings stating that although normal pressure hydrocephalus can occur in both men and women of any age, it is found more often in the elderly population, with a peak onset generally in the sixth to seventh decades.
Patients with dementia that are confined to a nursing home and may have undiagnosed NPH, can possibly become independent again once treated. So far only one study was able to evaluate the prevalence of NPH, both diagnosed and undiagnosed, among residents of assisted-living facilities, showing a prevalence in 9 to 14% of the residents.
, gait disturbance, and dementia
(commonly referred to as "wet, wobbly and wacky" or "weird walking water").
, followed by the evaluation of clinical response to removal of CSF. This can be followed by a CT, MRI
, and continuous external lumbar CSF drainage during 3 or 4 days.
to drain excess cerebrospinal fluid to the abdomen where it is absorbed. Once the shunt is in place, the ventricles usually diminish in size in 3 to 4 days, regardless of the duration of the hydrocephalus. Even though the ventricular swelling diminishes, only 21% of patients show a marked improvement in symptoms. The most likely patients to show improvement are those that show only gait disturbance, mild or no incontinence, and mild dementia. A more recent study (2004) found better outcomes, concluding that if patients with idiopathic normal pressure hydrocephalus are correctly identified, shunt insertion yielded beneficial outcomes in 86% of patients, in either gait disturbance (81%), improved continence (70%), or both. They also observed that measurements in the diagnostic clinical triad, the cortical sulci size, and periventricular lucencies were related to outcome. However, other factors such as age of the patient, symptom duration, dilation of ventricles, and the degree of presurgical dementia were unrelated to outcome.
Intracranial pressure
Intracranial pressure is the pressure inside the skull and thus in the brain tissue and cerebrospinal fluid . The body has various mechanisms by which it keeps the ICP stable, with CSF pressures varying by about 1 mmHg in normal adults through shifts in production and absorption of CSF...
(ICP) due to an abnormal accumulation of cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
(CSF) in the ventricles of the brain, which can cause ventriculomegaly
Ventriculomegaly
Ventriculomegaly is a brain condition that occurs when the lateral ventricles become dilated. The most common definition uses a width of the atrium of the lateral ventricle of greater than 10 mm. This occurs in around 1% of pregnancies. When this measurement is between 10 and 15 mm, the...
. The ICP gradually falls but still maintains a slightly elevated level and the CSF pressure reaches a high normal level of 150 to 200 mmH2O. Measurements of ICP, therefore, are not usually elevated. Because of this equilibration, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness. (Though some studies have shown pressure elevations to occur only intermittently). However, the enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient. The classic triad of gait disturbance, urinary incontinence, and dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
or mental decline, was first described by Hakim and Adams in 1965. NPH is often misdiagnosed as Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
, or dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
, due to its chronic nature and nonspecfic presenting symptoms [see below]. Although the exact mechanism is unknown, normal-pressure hydrocephalus is thought to be a form of communicating hydrocephalus with impaired CSF reabsorption at the arachnoid granulations.
There are 2 types of normal pressure hydrocephalus: idiopathic and secondary. The term idiopathic means that it has no known cause. The secondary type of NPH can be due to a subarachnoid haemorrhage, head trauma, tumour, CNS infection, or a complication of cranial surgery.
Recent population-based studies have estimated the prevalence of NPH to be about 0.5% in those over 65 years old, with an incidence of about 5.5 patients per 100,000 of people per year. This is in accordance with comparable findings stating that although normal pressure hydrocephalus can occur in both men and women of any age, it is found more often in the elderly population, with a peak onset generally in the sixth to seventh decades.
Patients with dementia that are confined to a nursing home and may have undiagnosed NPH, can possibly become independent again once treated. So far only one study was able to evaluate the prevalence of NPH, both diagnosed and undiagnosed, among residents of assisted-living facilities, showing a prevalence in 9 to 14% of the residents.
Clinical manifestations
NPH may exhibit a classic triad of clinical findings (known as the Adams triad or Hakim's triad) of urinary incontinenceUrinary incontinence
Urinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...
, gait disturbance, and dementia
Dementia
Dementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
(commonly referred to as "wet, wobbly and wacky" or "weird walking water").
- Gait disturbance is typically the initial and most prominent symptom of the triad and may be progressive, due to expansion of the ventricular system, particularly at the level of the lateral ventricles, leading to traction on the corticospinal motor fibers descending to the lumbosacral spinal cord. The gait disturbance can be classified as mild (cautious gait or difficulty with tandem gait), marked (evident difficulty walking or considerable unstable gait) or severe (unaided gait not possible) In the early stages, most often this gait disturbance occurs in the form of unsteadiness and impaired balance, especially when encountering stairs and curbs. Weakness and tiredness of the legs may also be part of the complaint, although examination discloses no paresisParesisParesis is a condition typified by partial loss of voluntary movement or by impaired movement. When used without qualifiers, it usually refers to the limbs, but it also can be used to describe the muscles of the eyes , the stomach , and also the vocal cords...
or ataxiaAtaxiaAtaxia is a neurological sign and symptom that consists of gross lack of coordination of muscle movements. Ataxia is a non-specific clinical manifestation implying dysfunction of the parts of the nervous system that coordinate movement, such as the cerebellum...
. Often a mobility aid is used for added stability, once the patient has reached the mild to marked stage. Such aids may include a quad cane or wheeled walker. The patient's gait at the marked stage will often show a decrease in step height and foot-floor clearance, as well as a decrease in walking speed. This style is often referred to as a magnetic gaitMagnetic gait-Presentation:Feet seem attached to floor as if by a magnet. In magnetic gait, each step is initiated in a "wresting" motion carrying feet upward and forward. Magnetic gait can be visualized in terms of a powerful magnet being forcefully pulled from asteel plate....
, in which the feet appear to be stuck to the walking surface, and is considered the characteristic gait disturbance of NPH. The gait may begin to mimic a Parkinsonian gaitParkinsonian gaitParkinsonian gait is the type of gait exhibited by patients suffering from Parkinson's disease . This disorder is caused by a deficiency of dopamine in the basal ganglia circuit leading to motor deficits...
, with short shuffling steps and stooped, forward-leaning posture, but there is no rigidity or tremor. An increased tendency to fall backwards is also seen, and a broad-based gait may be employed by the patient in order to increase their base of support and thereby their stability. In the very late stages, the patient can progress from an inability to walk, to an inability to stand, sit, rise from a chair or turn over in bed; this advanced stage is referred to as "hydrocephalic astasia-abasia"
- DementiaDementiaDementia is a serious loss of cognitive ability in a previously unimpaired person, beyond what might be expected from normal aging...
is predominantly frontal lobe in nature and of the subcortical type of dementia. It presents in the form of apathy, forgetfulness, inertia, inattention, decreased speed of complex information procession (also described as a dullness in thinking and actions), and disturbed manipulation of acquired knowledge, which is reflective of the loss of integrity of the frontal lobes. Memory problems are usually a component of the overall problem and have been predominant in some cases, which can lead to the misdiagnosis of Alzheimer's disease. However, in NPH there may be an obvious discrepancy between (often severely) impaired recall and intact or much less impaired recognition. The dementia is thought to result from traction on frontal and limbic fibers that also run in the periventricular region.
- Urinary incontinenceUrinary incontinenceUrinary incontinence is any involuntary leakage of urine. It is a common and distressing problem, which may have a profound impact on quality of life. Urinary incontinence almost always results from an underlying treatable medical condition but is under-reported to medical practitioners...
appears late in the illness, and is found to be of the spastic hyperreflexic, increased-urgency type associated with decreased inhibition of bladder contractions and detrusor instability. In the most severe cases, bladder hyperreflexia is associated with a lack of concern for micturition due to the severe frontal lobe cognitive impairment. This is also known as "frontal lobe incontinence", where the patient becomes indifferent to their recurrent urinary symptoms.
Diagnosis
Diagnosis of NPH is usually first led by a lumbar punctureLumbar puncture
A lumbar puncture is a diagnostic and at times therapeutic procedure that is performed in order to collect a sample of cerebrospinal fluid for biochemical, microbiological, and cytological analysis, or very rarely as a treatment to relieve increased intracranial pressure.-Indications:The...
, followed by the evaluation of clinical response to removal of CSF. This can be followed by a CT, MRI
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...
, and continuous external lumbar CSF drainage during 3 or 4 days.
- Lumbar punctureLumbar punctureA lumbar puncture is a diagnostic and at times therapeutic procedure that is performed in order to collect a sample of cerebrospinal fluid for biochemical, microbiological, and cytological analysis, or very rarely as a treatment to relieve increased intracranial pressure.-Indications:The...
is usually the first step in diagnosis and the CSF opening pressure is measured carefully. In most cases, CSF pressure is usually above 155 mmH2O. Clinical improvement after removal of CSF (30 mL or more) has a high predictive value for subsequent success with shuntingCerebral shuntCerebral shunts are commonly used to treat hydrocephalus, the swelling of the brain due to excess buildup of cerebrospinal fluid . If left unchecked, the cerebral spinal fluid can build up leading to an increase in intracranial pressure which can lead to intracranial hematoma, cerebral edema,...
. This is called the "lumbar tap test" or Miller Fisher test. On the contrary, a "negative" test has a very low predictive accuracy, as many patients may improve after a shunt in spite of lack of improvement after CSF removal.
- Infusion test is a test with higher sensitivity and specificity than a lumbar puncture. The outflow conductance (Cout) of the cerebrospinal fluid (CSF) system is a parameter considered to be predictive in selection for hydrocephalus surgery. Cout can be determined through an infusion test.
- In some centers, External lumbar drainage has been shown to have the highest sensitivity and specificity with regards to predicting a successful outcome following surgery.
- CT scan may show enlarged ventricles without convolutional atrophy.
- MRI may show some degree of transependymal migration of CSF surrounding the ventricles on T2/FLAIR sequence. Imaging however cannot differentiate between pathologies with similar clinical picture like Alzheimer's dementia, vascular dementia or Parkinson's diseaseParkinson's diseaseParkinson's disease is a degenerative disorder of the central nervous system...
.
Treatment
NPH may be relieved by surgically implanting a ventriculoperitoneal shuntShunt (medical)
In medicine, a shunt is a hole or a small passage which moves, or allows movement of fluid from one part of the body to another. The term may describe either congenital or acquired shunts; and acquired shunts may be either biological or mechanical.* Cardiac shunts may be described as...
to drain excess cerebrospinal fluid to the abdomen where it is absorbed. Once the shunt is in place, the ventricles usually diminish in size in 3 to 4 days, regardless of the duration of the hydrocephalus. Even though the ventricular swelling diminishes, only 21% of patients show a marked improvement in symptoms. The most likely patients to show improvement are those that show only gait disturbance, mild or no incontinence, and mild dementia. A more recent study (2004) found better outcomes, concluding that if patients with idiopathic normal pressure hydrocephalus are correctly identified, shunt insertion yielded beneficial outcomes in 86% of patients, in either gait disturbance (81%), improved continence (70%), or both. They also observed that measurements in the diagnostic clinical triad, the cortical sulci size, and periventricular lucencies were related to outcome. However, other factors such as age of the patient, symptom duration, dilation of ventricles, and the degree of presurgical dementia were unrelated to outcome.
Shunts in Developing Countries
Since the cost of shunt systems, including the high cost of revisions, is beyond the reach of common people in developing countries, most of them die without ever receiving a shunt. Looking at this point, a study done by Dr. Benjamin C. Warf comparing different shunt systems and highlighting the role of a low cost shunt system in most of the developing countries. This study has been published in the Journal of Neurosurgery: Pediatrics May 2005 issue. It is about comparing the Chhabra shunt system from Surgiwear to those of the shunt systems from developed countries. The study was done in Uganda and the shunts were donated by International Federation for Spina Bifida and Hydrocephalus.External links
- Normal Pressure Hydrocephalus at Cleveland ClinicCleveland ClinicThe Cleveland Clinic is a multispecialty academic medical center located in Cleveland, Ohio, United States. The Cleveland Clinic is currently regarded as one of the top 4 hospitals in the United States as rated by U.S. News & World Report...
- Normal Pressure Hydrocephalus at Likvor