Swellings of proximal axons in a case of motor neuron disease.

Serial semithin sections of lumbar anterior horn cells from a patient with rapidly progressive sporadic motor neuron disease were searched for direct connections between swellings of neuronal processes and perikarya. Focal swellings of the proximal axons were not uncommonly seen to be connected directly to perikarya. These swellings varied in shape and size and some were identified as spheroids. Most of the cell bodies connected with swellings showed otherwise normal architecture. These observations suggest that the focal swellings of proximal axons, particularly the distal portion of the initial segment and the first internode of the myelinated axon, indicate an early pathological change, and may represent functionally and morphologically vulnerable sites.