The future can be bleak for patients with Alzheimer’s disease or other forms of dementia because these conditions rarely can be reversed. Yet there’s evidence that about 5% of patients diagnosed with dementia actually have an unrecognized—and treatable—condition.
It’s believed that an estimated 700,000 people in the US have excessive fluid in the brain, a condition called normal pressure hydrocephalus (NPH). The fluid presses against the brain, causing poor balance, memory loss and other symptoms similar to dementia.
NPH occurs almost exclusively in adults 55 years old or older. It’s called “normal pressure” because fluid accumulates so gradually that there isn’t the sharp spike in pressure that occurs with acute hydrocephalus.
Cavities within the brain called ventricles produce about a pint of cerebrospinal fluid a day. This fluid, which cushions the brain and spinal cord, is normally reabsorbed by tissues at about the same rate as it is produced.
In patients with NPH, the fluid is reabsorbed more slowly. This usually occurs because of scar tissue within brain membranes. The scarring, caused by factors such as inflammation, previous hemorrhages (strokes) or a traumatic head injury, impedes normal drainage. Excess fluid enlarges the ventricles.
Pressure from accumulated fluid presses against nerves and other brain tissues. It also can compromise blood vessels, decreasing blood flow to the brain.
Result: Dementia-like symptoms.
Most patients with NPH exhibit three key symptoms…
Why it’s missed: The same symptoms can be caused by many different conditions, including a stroke, Alzheimer’s disease or other forms of dementia. Urinary incontinence could be due to a prostate problem. Balance problems often are due to spine diseases, diabetes or inner-ear problems.
A CT or MRI scan will show if a patient has enlarged ventricles, but this isn’t always caused by NPH. It’s normal, for example, for the ventricles to enlarge with age. It can be difficult to distinguish normal enlargement from ventricle changes due to fluid pressure.
Problems with gait and balance typically are the first symptom of NPH—memory loss usually comes later. This is the opposite of what happens with Alzheimer’s, in which cognitive symptoms usually occur first.
If a neurologist suspects that a patient has NPH, an imaging test will reveal, to some degree, whether ventricular enlargement is caused by excess fluid.
Next step: The removal of excess fluid. If a patient has NPH, removing as little as 50 cubic centimeters (cc’s), about 10 teaspoons, of fluid through a lumbar puncture (spinal tap) often will improve symptoms within a day.
Sometimes, a more involved procedure, lumbar catheter insertion, is necessary to diagnose NPH. A catheter is inserted into the area around the spinal cord. This permits continuous fluid removal (about a pint altogether) over 36 hours. The patient usually spends two nights in the hospital while fluid is removed from the brain. Then the catheter is removed, and he/she goes home for a few days. At a follow-up appointment, the neurologist retests the patient’s balance, cognitive abilities, etc. The doctor also will ask friends or family members if they have noticed an improvement in the patient’s symptoms.
If the patient improved significantly, then a diagnosis of NPH is virtually certain—particularly if the symptoms return when fluid levels in the brain gradually rise to pretreatment levels (within three to five days).
The only treatment for NPH is to insert a shunt, a silicone tube, in the brain that continuously drains excess fluid. Shunts are extremely durable and potentially can last for decades.
Best choice: A programmable shunt that allows the neurologist to fine-tune the settings and increase or decrease the rate at which fluid is removed from the brain. A doctor can make adjustments to the valve with an external device without additional surgery. The programmable shunt is more expensive but often is covered by insurance. Check with your provider.
The procedure to implant a shunt usually takes less than an hour. The device is inserted into the brain, and a drainage tube is implanted under the skin. This tube carries drained brain fluid into the abdominal cavity, where it’s absorbed into the bloodstream. Both the shunt and tube are invisible to others, although patients might notice a small bump on the head where the valve is implanted and a bump where the tube passes over the collarbone.
About 80% of patients who undergo the procedure experience significant improvements in memory, gait, etc. The improvements tend to be most dramatic in those who are diagnosed and treated early, before fluid buildup permanently damages brain tissue.
Although any brain procedure carries risk, shunt insertion is relatively safe. About 25% to 50% of patients undergo additional procedures to remove blockages from the shunt or drainage tube over the next two years.
