Hydrocephalus, Normal Pressure
Background
Normal pressure hydrocephalus (NPH) is an abnormal increase in cerebrospinal fluid (CSF) within the brain’s cavities, or ventricles, due to a blockage in the flow of CSF. The ventricles enlarge to accommodate the extra volume and begin to press on adjacent areas of the brain, increasing intracranial pressure; however, unlike other types of hydrocephalus, the CSF pressure tends to remain normal or is only slightly elevated. Another difference between NPH and other types of hydrocephalus is that increase in ventricular volume is not accompanied by an increase in the volume of CSF that flows through the membranes lining the brain.
The buildup of CSF in the ventricles occurs gradually; consequentially, the onset of symptoms is insidious. Their initial subtlety often delays patients from seeking care. The areas of the brain typically affected by normal pressure hydrocephalus are those associated with the legs, the bladder and cognitive mental processes, producing a constellation of corresponding symptoms which characterize NHP: abnormal gait, urinary incontinence, and dementia. Another factor delaying diagnosis is that most cases of NPH occur in patients over the age of 60, and these symptoms can be erroneously dismissed as normal signs of aging.
Causes/Risk Factors
In about half of all cases of normal pressure hydrocephalus the disturbance in CSF flow can be linked to head trauma, subarachnoid hemorrhage, stroke, or meningitis. In the remainder of cases the cause is not clear.
Symptoms
The characteristic symptoms of normal pressure hydrocephalus are urinary incontinence, dementia, and gait disturbance—a difficulty initiating movement and short, shuffling steps with postural instability. The classic symptoms of other forms of hydrocephalus may or may not be present, including headache, lethargy, nausea, vomiting, weakness, and altered consciousness.
Diagnosis
The triad of gait abnormality, dementia and urinary incontinence should raise the suspicion of normal pressure hydrocephalus as opposed to other conditions. Tests to confirm the diagnosis include neuropsychological testing to assess dementia and imaging studies (MRI and CT) to identify ventricular enlargement. A spinal tap may also be performed to analyze CSF content and/or temporarily relieve pressure.
The dementia of normal pressure hydrocephalus is similar to that of Alzheimer’s and the gait problems are similar to those of Parkinson’s, so misdiagnosis of NPH as one of these diseases is a concern. Correct diagnosis is important because the effects of NPH can potentially be reversed with proper treatment, whereas Alzheimer’s and Parkinson’s cannot.
Treatment
Surgical CSF shunting can provide relief of symptoms for some patients. In this procedure a thin tube is inserted in the ventricles to drain fluid away from the brain to another part of the body where it can be absorbed into the bloodstream. A trial is used to determine whether or not the patient is a good candidate for the procedure. The trial consists of a neuropsychological evaluation and timed walking test, followed by a lumbar puncture (spinal tap) which drains a prescribed amount of CSF. A few hours later the psychological and walking tests are administered again, and the results are compared with the initial tests. An improvement in mental status or gait predicts a favorable response to surgery. However, the decision to implant a shunt is considered in association with the patient’s overall health.
Prevention
Currently there are no guidelines for preventing normal pressure hydrocephalus.