Skeletal muscle of cattle affected with progressive degenerative myeloencephalopathy.

Skeletal muscle from multiple sites of 6 cattle afflicted with progressive degenerative myeloencephalopathy was analyzed by transmission electron microscopy and compared with skeletal muscle taken from 2 clinically normal cattle (controls) similarly studied. Major changes in the affected muscle included abnormal myoneural junctions with redundant junctional folds that were abnormally long and branching, and occasionally separated from the synaptic site; multiple vacuoles of variable size clustered in subsarcolemmal positions and in rows between myofibrils; bizarre mitochondria with thin connecting stalks, large electron-dense bodies, and abnormal cristae; and cone-shaped projections of the sarcolemma. These findings indicate that myopathy is part of the progressive degenerative myeloencephalopathy phenotype.