Normal Pressure Hydrocephalus

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, 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 (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 nonspecific presenting symptoms . 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 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.

Read more about Normal Pressure Hydrocephalus:  Clinical Manifestations, Diagnosis, Treatment, Shunts in Developing Countries

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