Friday, November 28, 2014

NPH: Not Neil Patrick Harris, Normal Pressure Hydrocephalus

Today we discussed an interesting case of progressive dementia with marked gait abnormality.  The team described the gait abnormality as "magnetic".  The clinical course of this patient also included urinary incontinence, and ultimately an MRI confirmed enlarged ventricles, consistent with Normal Pressure Hydrocephalus.

Figure 1: Magnetic boots from Faceoff

What is NPH?

NPH is a rare disease characterized by the clinical triad of (gait disturbance, worsening cognitive function and urinary incontinence).  The gait classicaly in NPH is described as being "magnetic" as patients have great difficulty with taking a step, and lifting their feet off of the ground.  This gives the appearance that their shoes are magnetically attracted to the floor.

The pathophysiology of NPH is thought to be related to widespread dysfunction of CSF re-absorption at the level of the arachnoid granulation.  Over time, the ventriculomegaly and high levels of CSF causes edema, and microvascular ischemia leading to the neurological deficits.


The diagnosis is suspected if a patient has the clinical triad and neuroimaging showing ventriculomegaly and periventricular white matter edema.  The next best diagnostic test is a lumbar puncture to both confirm the normal CSF pressure, and also to demonstrate clinical improvement with the removal of >30 cc of CSF.  This is the so called "Fisher" test, where neurocognitive and gait assessments are done before and after the removal of large volumes of CSF, and if a patient has a signficiant clinical improvement than this would be consistent with the diagnosis of NPH.
Figure 2: Ventriculomegaly and white matter edema


The most widely utilized treatment in patients with confirmed NPH is the placement of a ventricular-peritoneal shunt (VP-shunt).  The reduces the amount of CSF in the ventricles and has demonstrated clinical improvement in many patients.  Other potential therapies include intermittent large volume lumbar punctures, and case reports also discuss the use of acetazolamide.

The Bottom Line:
NPH is one of the "reversible" causes of dementia, and internists need to have a high index of suspicion in order to make this diagnosis.  The diagnosis is also complicated by the fact that many patients with Alzheimer's dementia have urinary incontinence and also demonstrate ventriculomegaly related to underlying atrophy.  The "Fisher test", and having the persistence to perform a lumbar puncture and document clinical improvement is really the only way to make the diagnosis.

Reference: Normal Pressure Hydrocephalus: How often does the diagnosis hold water.  Klassen et al. Neurology 2011.