Single-cell elderly blood-CSF atlas implicates peripherally-influenced neuroinflammatory degeneration in normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a common, yet enigmatic form of dementia characterized by cerebral ventriculomegaly. In contrast to other types of hydrocephalus, iNPH exhibits normal or even reduced intracranial pressures and infrequent reductions in ventricular size after CSF shunting. Here, we generated the first single-cell RNA sequencing atlas of the peripheral blood and ventricular CSF in elderly iNPH patients totaling 140,207 transcriptomes. Integrated analyses identified a pro-inflammatory signature in peripheral blood and CSF monocytes that was significantly enriched in iNPH subgroups with lower cognitive function. We also identified novel CSF cell populations likely representing the periventricular sloughing of degenerating neuroglial cells. Our findings suggest that immune dysregulation detectable in peripheral blood monocytes contributes to CSF space inflammation, neurodegeneration, and associated cognitive deficits in iNPH. These data shift the paradigm of iNPH from a primary disorder of impaired “brain plumbing” and highlight the potential for non-invasive, immune-based diagnostic and treatment strategies.