An electrophysiological quantitation of the cubital tunnel syndrome.

Four hundred and ninety-two ulnar nerves were studied in 237 patients with cubital tunnel syndrome and 233 subjects without clinically apparent ulnar neuropathy. Terminal motor and sensory latencies, motor and sensory conduction velocities, sensory action potential amplitudes and dispersons, and needle electromyography were analysed by a 0 to 10 rating--the EMG score. The patients were clinically graded from 1 (least severe) to 4 (most severe). The median EMG scores of these were 0.9/10 (N = 70); 1.6/10 (N = 81); 4.7/10 (N = 46); and 7.1/10 (N = 56), respectively. The median EMG score for the controls was 0.6/10 (N = 239) and 14.7% had asymptomatic ulnar entrapments. This incidence reached 30% in controls who were 60 years or older. In 25 other controls, the above sulcus sensory action potential was analysed. Its mean dispersion was 4.9 +/- 1.0 s-3. This measurement was significantly prolonged in 84.6% of 13 studies in which the EMG score was 0/10. These patients had either sensory symptoms only or an additional mild sensory deficit. Comparison of the EMG score obtained with sequential studies would allow one to objectively evaluate improvement or deterioration of the clinical state, giving a rational means of determining the need for surgery.