Normal pressure hydrocephalus (NPH): ischaemia, CSF stagnation or both

Normal pressure hydrocephalus (NPH) is a clinical and radiographic syndrome first described by Hakim and Adams in 1965 (Hakim and Adams, 1965) and characterized clinically by gait apraxia (‘magnetic gait’), incontinence and dementia, and diagnosed predominantly among people over the age of 60 years. Only a minority of patients present with the complete triad of symptoms, gait apraxia being the most common presenting complaint. On brain imaging, one sees ventricular enlargement without significant cerebral atrophy. The radiographic observation that best distinguishes the ventriculo‐megaly of NPH from the ‘hydrocephalus ex vacuo ’ of advanced Alzheimer’s disease is the degree of dilatation of the peri‐hippocampal fissures (PHFs). PHFs are normal or only minimally dilated in NPH, and typically markedly dilated in Alzheimer’s disease. The ‘normal pressure’ aspect of NPH is something of a misnomer. While CSF pressure may be within the normal range when measured by manometry at lumbar puncture, continuous CSF pressure measurements reveal waves of increased pressure, particularly during rapid eye movement (REM) sleep, and CSF infusion studies reveal abnormal CSF circulation. Sceptics may doubt the existence of NPH as a clear‐cut clinical–pathological entity (Bret et al., 2002). Among ‘believers,’ most accept CSF shunting as a reasonably effective treatment for the gait disorder of NPH. The effectiveness of CSF shunting as a useful treatment for the dementia of NPH has never been demonstrated, and many doubt that there is a rationale for such an approach among …