F waves in patients with hand wasting caused by a cervical rib and band.

In five patients with unilateral wasting of the hand muscles as a result of cervical rib and band, F waves were recorded from the hypothenar muscles following stimulation of the ulnar nerve at the wrist. Twelve healthy control subjects were also examined. F-wave latency was consistently increased in the affected hands of the patients, compared with results from the unaffected and control hands. This increase persisted after removal of the cervical band in four patients and was thought to be mainly due to degeneration of fast-conducting fibers. In the fifth patient, F-wave latency decreased after operation, suggesting recovery of a local conduction block in the proximal part of the nerve.