AXONAL LOSS FROM THE OLFACTORY TRACTS IN ALZHEIMERS-DISEASE

Senile dementia of the Alzheimer type has been shown to be associated with impaired olfactory function early in the course of the disease. Neuropathology in the olfactory system is also a feature of Alzheimer's disease (AD) and it has been suggested that the disease may be caused by a pathogen entering the brain via olfactory pathways. To investigate this hypothesis, the effect of AD on the olfactory tract was investigated. There was a 40% decrease in the cross-sectional area of the olfactory tract and a 52% loss of myelinated axons from the tract in AD. These results, together with those of previous studies suggest that peripheral regions of the olfactory system, i.e., the olfactory bulb and primary sensory olfactory neurons are less affected by the pathology of AD than more central parts, i.e., cortical regions, the anterior olfactory nuclei, and olfactory tract. This less severe pathology at the periphery argues against a pathogen entering the brain via the peripheral olfactory apparatus and suggests a central pathogenesis which spreads centrifugally along olfactory pathways.