Impact of disuse muscular atrophy on the compound muscle action potential.

BACKGROUND

Disuse atrophy from immobilization is the result of decreased neural activity and muscle unloading.

METHODS

We studied the impact of disuse on hand intrinsic compound muscle action potentials (CMAPs) in a cohort of 39 patients with unilateral 6-week immobilization of the hand in a cast, after distal radius fracture. We excluded patients with nerve injury. We compared side-to-side CMAP characteristics at the time of cast removal and at a subsequent follow-up visit, after a mean interval of 7.8 weeks.

RESULTS

Statistically significant reductions in CMAP amplitude were noted for the abductor pollicis brevis (29.2%), abductor digiti minimi (19.0%), and first dorsal interosseus (24.9%). There was partial repair of the relative CMAP reduction at the follow-up visit (20.1%, 10.7%, and 8.7%, respectively). There was no significant change in CMAP duration.

CONCLUSIONS

These results provide a framework for quantifying the degree of hand intrinsic CMAP amplitude reduction attributed to disuse.