A reversible dementia

Ann-Marie Yost, M.D.
Neurosurgeon, Providence Brain and Spine Institute
The Oregon Clinic

Published March 2013

Symptoms such as an unsteady gait, cognitive impairment and urinary frequency or incontinence easily can be mistaken for Alzheimer’s disease or the dementia component of Parkinson’s disease. Often, however, they’re the result of normal pressure hydrocephalus.

This abnormal accumulation of cerebrospinal fluid in ventricles is important to diagnose because with appropriate treatment, the symptoms can be relieved or even reversed.

Normal pressure hydrocephalus most often is idiopathic. Frequently it’s assumed to be present based on enlarged ventricles on scans, but it’s important to distinguish this from hydrocephalus ex-vacuo, which is caused by atrophy of the surrounding brain.

NPH occurs slightly more frequently in men, typically those who are older than 60. It usually begins insidiously with gait disturbance – an ataxic gait that also may include difficulty initiating movement and turning corners. Cognitive issues include memory and slowness of thought. Urinary incontinence most often is unwitting.

The exact etiology of NPH is unclear. One theory is a decrease in CSF absorption that leads to a transient elevation of pressure. The resulting ventricular enlargement causes the pressure to fall to normal, and in some patients may fluctuate intermittently to higher pressures.

The diagnosis is suggested by the presence of ventricular enlargement on a CT or MRI that isn’t explained by atrophy accompanied by the clinical symptoms mentioned above. Cine MRI demonstrating increased flow rate of CSF in the ventricles suggests NPH.

Once NPH is determined, there are a number of ways to learn whether shunting will be successful. One is cisternography, which involves injecting radionucleotide via lumbar puncture and monitoring the movement of the isotope over time. A normal study would show the isotope evenly distributed over the cerebral convexities at 24 hours with no lingering activity in the ventricles. A good prognosis is likely when the isotope remains in the ventricles 48 to 72 hours later.

Diagnostic testing consists of lumbar puncture – as a one-time tap or placement of a lumbar drain – and admission for monitoring over several days. Improved and shortened symptoms indicate a good response to the shunting.1

A ventriculoperitoneal shunt is the treatment of choice, most often with a programmable shunt. Because over drainage can cause subdural hematoma, a programmable shunt allows the amount of CSF drainage to increase slowly over time, thus allowing the brain to adjust and to decrease the risk. Potential complications of ventriculoperitoneal shunt placement are infection, hemorrhage and shunt failure.

After the patient’s successful shunt placement, symptoms should begin to improve, starting with less urinary incontinence, followed by improved gait and increased cognitive ability. Patients should be followed for six to12 months and should be evaluated for shunt reprogramming or replacement if they fail to improve or show persistent ventriculomegaly.1

In summary, an older person presenting with specific symptoms – three to six months of gait ataxia, cognitive slowing and memory difficulty, urinary incontinence, enlarged ventricles with sulcal flattening, elevated temporal horns (no atrophy), and with a good response to high-volume lumbar puncture or lumbar drainage – is likely to have the treatable form of dementia known as NPH and should be referred to a neurosurgeon.

The National Institutes of Health has ongoing trials on NPH. For more general information, visit the Hydrocephalus Association or National Hydrocephalus Foundation.

1Greenberg, Mark S. Handbook of Neurosurgery, 7th edition. Chapter. New York, N.Y., USA: Thieme; 2010