Prevalence of idiopathic normal-pressure hydrocephalus.

Objectives: The aim of this study was to determine the prevalence of idiopathic normal-pressure hydrocephalus (iNPH) in elderly persons in a large population-based sample using radiologic and clinical examinations.

Methods: We examined representative elderly populations aged 70 years and older that had undergone neuropsychiatric evaluations and CT of the brain between 1986 and 2000 (n = 1,238). Gait was evaluated by clinical examination and history of walking difficulty. Cognitive function was evaluated with the Mini-Mental State Examination and urinary incontinence by self-report. iNPH was diagnosed in concordance with the American-European iNPH guidelines. Exclusion criteria were history of meningitis, severe head trauma, and subarachnoid hemorrhage.

Results: The prevalence of probable iNPH was 0.2% in those aged 70-79 years (n = 2) and 5.9% (n = 24) in those aged 80 years and older, with no difference between men and women. Only 2 of these persons had been treated for iNPH. Hydrocephalic ventricular enlargement, i.e., a CT image consistent with NPH, was found in 56 persons (4.5%). An Evans Index >0.3 was found in 256 (20.7%) and occluded sulci at the high convexity in 67 persons (5.4%). All of these findings were more common in the older age groups.

Conclusions: Many elderly possess clinical and imaging features of iNPH, especially those older than 80 years. The number of persons with iNPH is probably much higher than the number of persons currently treated.