Frequency of Idiopathic Normal Pressure Hydrocephalus

To the Editor. —To our knowledge, epidemiologic studies concerning the incidence and prevalence of idiopathic normal pressure hydrocephalus (INPH) are not available and estimates of its frequency vary widely. The small amount of available data always refer to selected samples (most of all demented populations) and show frequencies ranging from 1%1,2to 5% and 6%3,4of all patients with dementia. However, it is probably misleading to group INPH and dementias together, since the disturbance of mentation in INPH is much more an "abulic trait" than a true dementia.5Furthermore, estimates based on demented populations alone may underestimate the true frequency of INPH, since mental impairment is not always part of the syndrome and, in many cases, the gait disturbance may be the only obvious symptom.5-7In a postmortem study performed on 205 brains of an adult population, Messert et al8found 5.5% of brains with