Plaque-like lesions in the basal forebrain in Alzheimer's disease

Silver staining (Bodian procedure) in the nucleus of the sublenticular substantia innominata (SI), also referred to as the nucleus basalis of Meynert, was evaluated in autopsy material from patients with Alzheimer's disease or senile dementia of the Alzheimer type (age at death: mean 69 years, range 63 to 81 years; time between onset of symptoms and death: mean 5.6 years, range 2.5 to 11.0 years). Although a decrease in the number of neurons and an increase in gliosis were observed in the SI in the Alzheimer dementia cases, classic senile plaques, as well as neurofibrillary tangles and granulovacuolar degeneration, were, with rare exception, not present in the basal forebrain. Small plaque-like lesions, 30-50 micron in diameter, were found scattered throughout the SI, however. These pathologic entities, like traditional senile plaques, demonstrated increased argentophilia compared to background, neuritic elements, and an increase in the number of glial cells. The magnitude of silver staining in the plaque-like lesions in the SI, however, was generally less than that associated with plaques in the cortex, hippocampus and amygdala. Although their significance is not known, plaque-like structures in the SI could represent the final degenerative phases of basal forebrain neurons and/or of fibers afferent to them. Their precise relationship to classic senile plaques remains to be elucidated.