Which of the following changes are known as reaction of degeneration following a peripheral nerve injury?

• A. Fatty degeneration of the muscle fibers
• B. Atrophy of muscle cells
• C. Degeneration of the nerve trunk
• D. Changes in the electrical reaction of the muscle fibers

Answer: (D)

After a peripheral nerve injury the muscle first shows its response through electrical changes rather than immediate structural changes. This reaction of degeneration reflects how the muscle fibers behave when they lose their nerve supply. Denervated muscle becomes electrically unstable, so on studies like EMG you see spontaneous activity in resting muscle, such as fibrillation potentials or positive sharp waves, and later changes in how the muscle responds to stimulation. These electrical alterations are the hallmark of the reaction of degeneration.

Fatty degeneration of muscle fibers and atrophy are true consequences of denervation over time, and degeneration of the nerve trunk describes Wallerian degeneration of the nerve itself, but the specific term “reaction of degeneration” refers to the altered electrical properties of the muscle fibers after denervation.