Deconstructing normal pressure hydrocephalus: Ventriculomegaly as early sign of neurodegeneration
Idiopathic normal pressure hydrocephalus (NPH) remains both over-suspected on clinical grounds and under-confirmed when based on immediate and sustained response to cerebrospinal fluid diversion. Poor long-term post-shunt benefits and findings of neurodegenerative pathology in most patients with adequate follow up suggests that hydrocephalic disorders appearing in late adulthood may often result from initially unapparent parenchymal abnormalities. We critically review the NPH literature, highlighting the near universal lack of blinding and controls, the absence of specific clinical, imaging, or pathologic features, and the ongoing dependence for diagnostic confirmation on variable cutoffs of gait response to bedside fluid-drainage testing. We also summarize our long-term institutional experience, in which post-shunt benefits in patients with initial diagnosis of idiopathic NPH persist in only 32% of patients at 36 months, with known revised diagnosis in over 25% (Alzheimer disease, dementia with Lewy bodies, and progressive supranuclear palsy). We postulate that previously reported NPH cases with “dual” pathology (i.e., developing a “second” disorder) more likely represent ventriculomegalic presentations of selected neurodegenerative disorders in which benefits from shunting may be short-lived, with a consequently unfavorable risk-benefit ratio. This article is protected by copyright. All rights reserved.