Ultrastructure of swollen proximal axons of anterior horn neurons in motor neuron disease

We have investigated ultrastructurally swellings of the proximal axons directly connected with the somata of anterior horn cells in a patient with motor neuron disease. In the distal portion of the initial segment, the swellings consisted predominantly of increased amounts of neurofilaments running nearly parallel to the longitudinal axis together with other cytoplasmic organelles. In the first internode of the myelinated axon, as the swellings became larger, the neurofilaments lost their parallel orientation and became intermingled. Most of the cell bodies connected with the swellings and their dendrites showed no particular changes. The abnormal neurofilamentous accumulations in the proximal axons suggest abnormal axonal transport, which may be pathogenetically associated with motor neuron disease.