Electromyographic motor Tinel's sign in ulnar mononeuropathies at the elbow.

Abstract

A novel test for localizing ulnar mononeuropathies (UM), the electromyographic (EMG) motor Tinel's sign, has been developed. While recording with a monopolar needle from the abductor digiti minimi, the ulnar nerve is lightly rolled at multiple sites across the elbow, and the test is considered positive if a burst of EMG activity is observed simultaneously with nerve compression. To determine the use of the EMG Tinel's sign, we evaluated 70 control nerves and 50 clinically suspected UMs. The EMG Tinel's sign had a 78% sensitivity and a 79% specificity for suspected UM at the elbow. The clinical Tinel's sign was present in 68% of suspected UM cases, and the combined sensitivity of the EMG and clinical Tinel's sign was 96%. Using nerve conduction study (NCS) values derived from the control nerves, 62% of UM nerves had abnormal NCS/EMG findings, and 28% of UM nerves had NCS/EMG abnormalities that could be localized to the elbow. The development of motor axon mechanosensitivity at the site of nerve injury is a new finding, not previously observed in electrophysiologic studies of animal nerve injury models or reported in the electrodiagnostic literature.