Focal pathology in the Edinger-Westphal nucleus explains pupillary hypersensitivity in Alzheimer's disease

Patients who suffer from Alzheimer's disease (AD) and a sub-population of c ommunity-dwelling elders show an exaggerated pupillary reaction to dilute t ropicamide, a cholinergic antagonist. This finding may serve as an early di agnostic marker of AD. Here we report a likely pathological basis for this hypersensitive pupillary response. Our observations indicate that the Eding er-Westphal nucleus (EW), a known center for the control of pupillary funct ion, is a selective target of Alzheimer pathology early in the course of th e disease. In all AD cases examined, the EW contained plaques and tangles. In contrast, the adjacent somatic portion of the oculomotor complex was vir tually spared of pathology. Early pathology in the EW is likely to initiate a cascade of events that may give rise to pupillary hypersensitivity.