Reflections on the diagnosis ‘Normal Pressure Hydrocephalus’

Abstract

The classification of neurodegenerative diseases, including normal pressure hydrocephalus, is confusing and problematical. Are they a continuum of clinical and pathological change or discrete and identifiable disorders in their own right? Can a meaningful consensus be constructed between clinical and pathological findings to justify allocation to a diagnostic category? In general in medicine three nosological classes may be defined. In the first related conditions are clearly distinguished and identified by emphatic clinical and pathological discontinuities. In the second there is overlapping and this compromises discrimination. In the third some differences do exist but the extent of the overlapping suggests a common pathology or even identity. The integrity of the diagnosis ‘normal pressure hydrocephalus’ is examined and in the absence of biomarkers and gold standards, a difficulty shared with psychiatric diagnoses, the diagnostic title is found wanting. It does not qualify for any of the nosological classes as defined. Four problems are identified: the first relates to the existence of intracranial pressure B-waves, the second to the frequent existence of confounding comorbidities, the third to the lack of controlled clinical trials to assess the efficacy of shunts and the fourth to the use of ‘patient-response’ to the insertion of a shunt as a gold standard to establish the diagnosis. The hypothesis is advanced that normal pressure hydrocephalus is an indeterminate syndrome and that the title should revert to ‘hydrocephalic syndrome’ as originally proposed by Hakim and Adams. The present confusion involving this syndrome and the neurodegenerative diseases in general will be eventually resolved by the continuing emergence of definitive gold standards based on advances in genetics, molecular pathology, nuclear medicine and neuroimaging.