Distribution of amyloid in the brainstem of patients with Alzheimer disease.

A4 protein (beta-protein, beta-amyloid) deposits were identified with silver stains in postmortem brainstem sections from 13 patients with Alzheimer disease (AD), 6 patients with mixed Alzheimer disease and Parkinson disease (AD-PD), 5 disease controls, and 2 elderly controls. A rostro-caudal gradient of A4 was found in patients with AD and AD-PD, such that A4 was most prevalent in the midbrain and least prevalent in the medulla. The brainstem of the controls contained little or no A4. The midbrain tectum and tegmentum contained the greatest densities of A4, but the red nucleus and substantia nigra pars reticulata were largely spared. This distribution of A4 suggests that A4 deposition is a function of synaptic connectivity rather than passive diffusion from vascular sources.