Prevalence of possible idiopathic normal-pressure hydrocephalus in Japan: The Osaki-Tajiri project

Background: Several studies have reported that the prevalence of idiopathic normal-pressure hydrocephalus (iNPH) was between 0 and 5%. However, the precise prevalence in a community-based elderly population remains unclear. We investigated the prevalence of possible iNPH retrospectively using an age- and gender-stratified random sample database. Methods: Five hundred and sixty-seven participants were randomly selected from among the 1,654 members of the population aged 65 years and older in Tajiri, Japan, and 497 underwent MRI. We classified participants as having possible iNPH if they had: (1) ventricular enlargement, as shown by an Evans index of ≥0.3, with closing sulci at the high convexity with dilation of the sylvian fissure on MRI, (2) at least one of the iNPH clinical triad (gait disturbance, urinary incontinence and cognitive impairment), and (3) no identifiable potential secondary cause of hydrocephalus. Results: We found 7 participants who met the criteria mentioned above. Cognitive impairments were the most common symptoms (n = 6) followed by gait disturbances (n = 3); however, urinary incontinence was not observed. No full clinical triad was present in the patients and only 3 participants had 2 of the triad. Conclusions: We considered the prevalence of possible iNPH in elderly adults to be 1.4% (95% confidence interval = 0.6-2.9%).