Histochemical and morphologic changes in skeletal muscle following cervical cord injury: a study of upper and lower motor neuron lesions.

The effects of upper and lower motor neuron lesions on human skeletal muscles and muscle spindles were studied using histochemical and morphometric techniques. In the lower motor neuron lesions, the muscle fibers showed group atrophy, fiber type grouping and target fibers. The muscle spindle demonstrated thickening of the capsule, degeneration of the nuclear chain fibers, targeting and splitting of the bag fibers. In the upper motor neuron lesion, the muscles showed group atrophy with histochemical evidence of preferential type II fiber involvement. Histometrics, however, failed to demonstrate type II fiber atrophy but showed hypertrophy of type I fibers. The muscle spindles only showed increased number of intrafusal fibers.