Cortical brain biopsy in long-term prognostication of 468 patients with possible normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) can be alleviated by cerebrospinal fluid shunting but the differential diagnosis and patient selection are challenging. Intraventricular intracranial pressure monitoring as part of the diagnostic workup as well as shunting enable to obtain cortical brain biopsies to detect amyloid-β (Aβ) and hyperphosphorylated tau (HPτ), the hallmark lesions of Alzheimer's disease (AD). In possible NPH, Aβ alone indicates an increased risk of AD and when present with HPτ probable AD, but the effect of those brain lesions on survival is not known. The aim of this study was to evaluate the predictive value of brain biopsy for the long-term outcome of possible NPH. Between 1991 and 2006, the Neurosurgery Department of the Kuopio University Hospital evaluated 468 patients for possible NPH by intraventricular intracranial pressure monitoring and frontal cortical brain biopsy immunostained against Aβ and HPτ. All patients were followed up until the end of 2008 (n = 201) or death (n = 267) with a median follow-up of 4.6 years (range 0-17). Logistic regression analysis with Cox models was applied. Out of the 468 cases, Aβ was detected in 197 (42%) cortical biopsies, and together with HPτ in 44 (9%). Aβ alone indicated increased risk of AD and with HPτ probable AD, but it did not affect survival. Vascular aetiology was the most frequent cause of death. Cortical biopsy findings indicate that NPH is at present a heterogeneous syndrome and has notable overlapping with AD. Brain biopsy did not predict survival but may open a novel research window to study the pathobiology of neurodegeneration.