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 community-dwelling elders show an exaggerated pupillary reaction to dilute tropicamide, a cholinergic antagonist. This finding may serve as an early diagnostic marker of AD. Here we report a likely pathological basis for this hypersensitive pupillary response. Our observations indicate that the Edinger-Westphal nucleus (EW), a known center for the control of pupillary function, is a selective target of Alzheimer pathology early in the course of the disease. In all AD cases examined, the EW contained plaques and tangles. In contrast, the adjacent somatic portion of the oculomotor complex was virtually spared of pathology. Early pathology in the EW is likely to initiate a cascade of events that may give rise to pupillary hypersensitivity.