Normal Pressure Hydrocephalus Diagnosis
A diagnosis on Normal Pressure Hydrocephalus (NPH) is based on:
- History, physical and neurological examination — dementia, difficulty walking and urinary incontinence
- Brain images to detect enlarged ventricles (CT or MRI scan)
As a rule, the earlier NPH is diagnosed, the better the chance for effective treatment. With early diagnosis and treatment, the symptoms of NPH can be effectively reduced. If a person with NPH is not treated, the symptoms will worsen over time, and the disorder will eventually lead to death.
Treating NPH as a Cause of Dementia
Dementia caused by NPH (about 5 percent of all dementia cases) is one of the few causes of dementia that is treatable. If a patient has experienced dementia for less than two years, his or her mental abilities can improve with treatment. If a patient has had dementia for more than two years, however, the likelihood of mental improvement is very small.
Tests to Diagnose Normal Pressure Hydrocephalus
The NPH Program team uses a variety of tests to help diagnose NPH, following guidelines developed by an international team of neurosurgeons. The guidelines were published in 2005 in Neurosurgery®, the official journal of the Congress of Neurological Surgeons.
Diagnosis starts with an initial examination in the NPH Clinic. Computed tomography (CT) or magnetic resonance imaging (MRI) is used to scan the brain for enlarged ventricles, an important test for patients with suspected NPH. If NPH is suspected based on a patient’s history, neurological examination, brief cognitive testing and brain imaging, the next steps include:
Cognitive testing, conducted by a neuropsychologist, to assess the patient for signs of dementia. A neuropsychologist specializes in assessing the effect of brain injury on behavior and cognition (the ability to think, reason and perceive). Testing involves answering questions and following simple directions to determine if there is a loss of brain function related to NPH. Neuropsychological testing can help give a more accurate diagnosis of cognitive problems and help in planning treatment.
Gait Walking and Balance Assessment
Gait (walking) and balance assessment, conducted by a physical therapist, assesses a person’s ability to walk. Walking difficulty is one of the major symptoms of NPH. During the assessment, a patient is videotaped while he or she is observed during standing and walking. The physical therapist assesses joint range of motion, speed, the quality of gait, and how the joints move.
A spinal tap (also called lumbar puncture), which allows an estimation of CSF pressure and an analysis of fluid. It is an outpatient test performed by a neurologist to determine if symptoms improve with removal of spinal fluid. Under local anesthetic, a thin needle is passed into the spinal fluid space of the low back. Up to 50cc (about 10 teaspoons) of CSF is removed.
Gait assessment is done right after the spinal fluid is removed to see if there is gait improvement. Six to eight hours after the spinal tap, gait and cognitive assessments are repeated to check for signs of improvement in walking and cognitive abilities. If symptoms improve (a positive outcome), a diagnosis of NPH can be confirmed, and the patient may then benefit from surgical placement of a shunt to permanently drain the fluid. When the response to a spinal tap is “negative” or uncertain, further evaluation may be helpful.
External Lumbar Drainage
External lumbar drainage, also called continuous lumbar drainage, is a variation of the lumbar puncture where a thin, flexible tube (catheter) is left in place to drain CSF. The procedure, which requires hospitalization, is performed by a neurologist to allow removal of spinal fluid over several days. This imitates the drainage effect that a shunt would have.
- During the first 24 to 48 hours, the spinal fluid pressure is monitored by a computer. NPH has a “signature” pressure reading.
- Over the next 24 to 48 hours, the spinal fluid is drained continuously at a rate of about 10cc (about 2 teaspoons) per hour. The total amount of spinal fluid drained is about half of the amount the body produces each day.
Each day of the 72-hour period, cognition and gait are tested to look for signs of improvement. If a patient shows improvement after the three-day period, a diagnosis of NPH can be confirmed, and it’s highly likely that the patient will benefit from a shunt. If a patient does not improve after 72 hours, the likelihood that a shunt will help the patient is very low.