The ultrastructure of intramuscular nerves in amyotrophic lateral sclerosis

Muscle biopsies of 11 patients suffering from amyotrophic lateral sclerosis (ALS) were examined and the i.m. nerves found in seven of them were examined by electron microscopy. In atrophied muscles there was a marked decrease of myelinated fibers. The ultrastructure of the remaining myelinated axons showed changes in the neurofilaments, mitochondria, and vesicles. There was a decrease in the number of unmyelinated fibers as well as the myelinated fibers. Occasionally, there was an increase of unmyelinated fibers containing small fine axons. There were corpora amylacea in unmyelinated axons and banded structures in the extracellular area of the Schwann cells of the unmyelinated fibers. Some of these findings were considered as the ultrastructural features of degeneration and regeneration in i.m. nerves of motoneurons in ALS.