Normal pressure hydrocephalus, also termed symptomatic hydrocephalus, is a type of brain
malfunction caused by decreased absorption of cerebrospinal fluid.
Its typical symptoms are gait disturbance, urinary incontinence, and dementia or mental
decline.
It is difficult to diagnose because the symptoms are common to several other diseases.
The usual treatment is installation of a shunt to drain excess CSF into another part of the
body.
This treatment can reverse the symptoms and restore normal functioning, or it may do so
partially, or it may not succeed.
NPH is caused by an increase in intracranial pressure due to an abnormal accumulation of
CSF in the ventricles of the brain, which can cause the ventricles to enlarge.
The intracranial pressure gradually falls but still remains slightly elevated, 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, patients do not exhibit the classic signs that accompany increased intracranial
pressure such as headache, nausea, vomiting, or altered consciousness, although some studies
have shown pressure elevations to occur intermittently.
However, the enlarged ventricles put increased pressure on the adjacent cortical tissue and
cause myriad effects in the patient.
The classic symptom triad 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 nonspecific 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 two types of normal pressure hydrocephalus: idiopathic and secondary.
The secondary type of NPH can be due to a subarachnoid haemorrhage, head trauma, tumour,
infection in the central nervous system, 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 who 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 of urinary incontinence, gait disturbance, and dementia.
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, marked or severe 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 paresis or ataxia.
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 gait, 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 gait, 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" Dementia 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, 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 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 incontinence 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 brain
imaging, either CT or MRI, to rule out any mass lesions in the brain.
This is then followed by lumbar puncture and evaluation of clinical response to removal
of CSF.
This can be followed by continuous external lumbar CSF drainage during 3 or 4 days.
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 disease.
Following imaging, lumbar puncture 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 has a high predictive value for subsequent
success with shunting.
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 that may have higher sensitivity and specificity than a lumbar
puncture, but is not performed in most centers.
The outflow conductance of the cerebrospinal fluid system is a parameter considered by
some centers to be predictive in selection for hydrocephalus surgery.
Cout can be determined through an infusion test.
This is not a test that is normally performed prior to shunting, but may become more accepted.
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.
Treatment NPH may be relieved by surgically implanting
a ventriculoperitoneal shunt 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 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, improved continence, 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.
References
External links The Normal Pressure Hydrocephalus Center at
Johns Hopkins Bayview Medical Center Normal Pressure Hydrocephalus at Cleveland
Clinic normal_pressure_hydrocephalus at NINDS
When it really is NPH at Likvor