The application of F-wave measurements in the differentiation of proximal and distal upper limb entrapments.

Conduction velocities of the proximal segments of the median and ulnar nerves were measured by evoking F-wave responses. The results of these and conventional motor and sensory studies from 60 control subjects were compared with the results in 30 patients with carpal tunnel syndromes, 18 patients with cubital tunnel syndromes, and 23 patients with suspected proximal entrapments. Sixty-seven percent of patients with proximal lesions (confirmed by myelography in 60 percent of cases) had abnormalities in their F-wave studies. Conventional motor studies were normal. Twenty-three percent of the patients with carpal tunnel syndrome and 11 percent of the patients with cubital tunnel syndrome also had abnormal F-wave studies, indicating an additional element of proximal entrapment. This technique is felt bo be useful in differentiating between distal and proximal entrapments.