Normal pressure hydrocephalus (NPH) is a rare disorder that is characterized by progressive gait difficulty, urinary incontinence and memory loss. Although the press has covered this topic extensively in both the written and video media, true normal pressure hydrocephalus remains quite uncommon. The underlying problem is actually an excessive build up of spinal fluid in the brain. The areas of the brain that stores this fluid are known as the ventricles. In NPH, the spinal fluid flows out of the brain but, due to reasons that are not entirely clear, there is a build up of excessive fluid in the brain. This results in enlarged ventricles causing a condition called communicating hydrocephalus.
Normal pressure hydrocephalus develops very slowly, over months to years. It is usually seen in individuals over the age of 65. As the ventricles slowly increase in size, affected patients begin to show signs of slowed, wide based, unsteady gait. Urinary incontinence may also develop during this time. Later during the disease process memory loss begins. All of the symptoms are very slowly progressive. Patients can be diagnosed incorrectly with Parkinson’s disease, Alzheimer’s disease, depression or just dementia.
The gait difficulty comes from the fact the the nerve fibers that control walking and balance become stretched as the ventricles enlarge. With this comes progressively worsening gait imbalance and falling. Patients may complain of weakness and fatigue. Patients will actually will tell you that their feet feel stuck to the ground, giving rise to the term magnetic gait. Memory loss seen in normal pressure involves mainly recall and slowness of thinking. Recognition of objects, tasks and individuals is better preserved. Without careful testing however, one can easily make the mistake of making an erroneous diagnosis of Alzheimer’s disease versus normal pressure hydrocephalus associated dementia. Urinary incontinence is a later finding in the disease process. There is an increasing need to urinate more frequently and urgently. If the dementia progresses too far, patients will become indifferent to their incontinence.
Diagnosis is made by obtaining an MRI or CT brain scan. The ventricles appear enlarged in the absence of brain atrophy (shrinkage.) As a normal process of aging, there is a certain amount of atrophy. It other conditions such as Alzheimer’s disease, alcoholism or in patient’s who have received chemotherapy, brain atrophy can be more prominent. The key in diagnosing NPH is that the degree of ventricular enlargement is out of proportion to the expected degree of atrophy. The degree of ventricular enlargement can be measured as a ratio to the degree of atrophy. The second step in diagnosis, after a complete neurological exam, is to do a diagnostic spinal tap (lumbar puncture.) During this procedure, 1-2 ounces of spinal fluid is drained off. The patient is then tested to see if their gait improves.
Treatment for confirmed cases of normal pressure hydrocephalus is a brain surgery procedure know as a ventriculoperitoneal shunt placement. In this procedure, a tube is placed in the ventricles and the other end drains into the abdomen. The tube is run under the skin. Spinal fluid is then absorbed in the abdomen. There is no known effective medical treatment for NPH. Early diagnosis and treatment is important as the gait disorder and urinary symptoms can be alleviated. Once the memory loss has begun, this cannot be reversed.
In order to have the accurate diagnosis of normal pressure hydrocephalus, a patient should be seen by a neurologist or neurosurgeon familiar with the condition. It is not necessarily easily diagnosed, even by experienced physicians. Nonspecific gait disorder is common with advancing age. Dementia is also common, particularly over the age of 70. Stroke, Parkinson’s disease and low thyroid can mimic the symptoms of normal pressure hydrocephalus. The main point is that of all these conditions, true normal pressure hydrocephalus occurs very rarely and is generally considered a diagnosis of exclusion of every other problem plus meet the diagnostic criteria listed above.