Specialty Neurology ICD-9-CM 331.9, 331.5 MedlinePlus 000752 | ICD-10 G91.2 DiseasesDB 9089 eMedicine neuro/277 radio/479 | |
Normal pressure hydrocephalus (NPH), also termed symptomatic hydrocephalus, is a type of brain malfunction caused by expansion of the lateral cerebral ventricles and distortion of the fibers in the corona radiata. Its typical symptoms are urinary incontinence, dementia, and gait disturbance. CSF pressure is usually normal. Ventricles are chronically dilated.
Contents
The usual treatment is surgical installation of a ventriculoperitoneal shunt to drain excess CSF into the lining of the abdomen where the CSF will eventually be absorbed.
Signs and symptoms
NPH may exhibit a classic triad of clinical findings (known as the Adams triad or Hakim's triad) of urinary incontinence, gait disturbance, and dementia (commonly referred to as "wet, wacky and wobbly" or "weird walking water").
Mechanism
NPH is caused by an increase in intracranial pressure (ICP) due to an abnormal accumulation of CSF in the ventricles of the brain, leading to ventriculomegaly. The intracranial pressure gradually falls but still remains slightly elevated, and the CSF pressure reaches a high normal level of 150 to 200 mm H2O. 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, enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient. The classic symptom triad (gait disturbance, urinary incontinence, and dementia) 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.
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.
Types
There are two types of normal pressure hydrocephalus: idiopathic and secondary. The secondary type of NPH can be due to a subarachnoid hemorrhage, head trauma, tumor, infection in the central nervous system, or a complication of cranial surgery.
Treatment
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.
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 (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.
Epidemiology
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.