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Image reprinted with permission from Medscape.com, 2011. Available at: medscape.com
Normal pressure hydrocephalus (NPH) is a clinical symptom complex characterized by abnormal gait, urinary incontinence, and dementia. It is an important clinical diagnosis because it is a potentially reversible cause of dementia. Normal pressure hydrocephalus usually occurs in older adults. The average age of people with NPH is older than 60 years. NPH is different than other types of hydrocephalus in that it develops slowly over time.
NPH differs from other causes of adult hydrocephalus. An increased subarachnoid space volume does not accompany increased ventricular volume or intracranial pressure.
Normal pressure hydrocephalus may begin with a transient high-pressure hydrocephalus with subsequent ventricular enlargement. With further enlargement of the ventricles, CSF pressure returns to normal; thus the term NPH, at least in view of the initial pathophysiologic events, is a misnomer. Intermittent intracranial hypertension has been noted in some patients.
Clinical symptoms result from the enlarged ventricles causing distortion of brain structures which include the sacral motor fibers that innervate the legs and the bladder, thus explaining the abnormal gait and incontinence. Compression of the brainstem structures could also be responsible for gait dysfunction, particularly the freezing of gait. Dementia results from distortion of the periventricular limbic system.
Causes
Normal pressure hydrocephalus may occur due to a variety of secondary causes but may be idiopathic in approximately 50% of patients. Secondary causes of NPH include head injury, subarachnoid hemorrhage, meningitis, and CNS tumor.
History
Patients present with a gradually progressive triad of symptoms which consist of abnormal gait, urinary incontinence, and dementia. The gait disturbance is typically the earliest feature noted and considered to be the most responsive to treatment. The gait of NPH is typically extremely slow, broad-based, magnetic, and shuffling. The urinary symptoms of NPH can present as urinary frequency, urgency, or frank incontinence. The dementia of NPH is characterized by prominent memory loss and slow mental processes. Particularly pronounced are deficits like forgetfulness, decreased attention and inertia.
The dementia symptoms of NPH can be similar to those of Alzheimer disease. The walking problems are similar to those of Parkinson disease. Experts believe that many cases of NPH are misdiagnosed as one of these diseases. The good news is that, unlike Alzheimer disease and Parkinson disease, NPH can be reversed in many people with appropriate treatment.
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