Normal pressure hydrocephalus is a brain disorder in which excess cerebrospinal fluid accumulates in the brain’s ventricles, which are fluid-filled chambers. NPH is called "normal pressure" because despite the excess fluid, CSF pressure as measured during a spinal tap is often normal. As brain ventricles enlarge with the excess CSF, they can disrupt and damage nearby brain tissue, leading to difficulty walking, problems with thinking and reasoning, and loss of bladder control.
NPH can sometimes be treated with surgical insertion of a shunt, a long, thin tube that drains excess CSF from the brain to the abdomen. Surgery is most likely to help correct difficulties walking, but thinking changes and loss of bladder control are less likely to improve. Shunting doesn’t help everyone with normal pressure hydrocephalus, and there’s uncertainty about how best to identify those most likely to benefit. There’s also a lack of data showing how long the benefit of shunting may last for those whose symptoms improve.
The following symptoms are considered hallmarks of NPH:
In some cases, NPH is caused by other brain disorders such as a tumor, head injury, haemorrhage, infection or inflammation. But in most cases, the cause of the fluid build-up remains unknown.
There is no single test to determine if someone has NPH. And even though the hallmark symptoms listed above are considered the ``classic`` signs of this disorder, not everyone with NPH has all of these symptoms.
Brain imaging to detect enlargement of the ventricles, often with magnetic resonance imaging (MRI), plays a key role in diagnosing NPH. Several brain disorders, including Alzheimer's disease, can cause overall brain tissue shrinkage that makes the ventricles look larger than normal. In NPH, although the ventricles are enlarged, brain tissue may not appear shrunken.
Because the symptoms of NPH may overlap with those of Alzheimer's and other dementias, experts recommend that a person with suspected NPH undergo examination by a neurologist with extensive experience evaluating brain disorders that affect movement, thinking skills and physical functions.
If symptoms and an MRI strongly suggest NPH, a large-volume spinal tap may be used to identify those who may benefit from a shunt. In this procedure, doctors remove a larger-than-usual amount of spinal fluid, and then observe the person for 30 to 60 minutes to note any improvements in walking or thinking and reasoning. Most people originally suspected of having NPH do not improve following a CSF removal test.