Normal pressure hydrocephalus: how often does the diagnosis hold water?

OBJECTIVE: To determine our community's incidence of clinically suspected normal pressure hydrocephalus (NPH), the rate of shunting for NPH, and short- and long-term outcomes of shunting.
METHODS: A retrospective query of the Mayo Clinic medical records linkage system was conducted to identify residents of Olmsted County, Minnesota, undergoing an invasive diagnostic procedure for evaluation of suspected NPH from 1995 through 2003. Among patients with shunts, early- and long-term outcomes were determined via a review of available medical records.
RESULTS: Forty-one patients underwent an invasive diagnostic procedure for evaluation of suspected NPH; 13 ultimately received shunts, representing an incidence of 1.19/100,000/year. The incidence of sustained definite improvements at 3 years after shunting was only 0.36/100,000/year. Definite gait improvement was documented in 75% at 3-6 months after shunt placement, although it dropped to 50% at 1 year and to 33% at 3 years. Only 1 of 8 patients with cognitive impairment and 1 of 6 patients with urinary incontinence had definite improvement in these symptoms at 3 years. No patient with moderate to severe postural instability experienced sustained definite improvement in any symptom. Complications occurred in 33% of patients including one perioperative death. Additional or alternative neurologic diagnoses later surfaced in 5 of 12 patients.
CONCLUSIONS: In this community, NPH is relatively rare with an incidence approximating that of progressive supranuclear palsy in this population. Whereas early gait improvement was common, only one-third of patients enjoyed continued improvement by 3 years; cognition or urinary incontinence was even less responsive long term. Baseline postural instability predicted poor outcome. Clinicians should balance potential benefits of shunting against the known risks.