Role of concentric needle Single Fiber Electromyography in detection of subclinical motor involvement in carpal tunnel syndrome

Background Conventional motor nerve conduction studies are usually normal in early and mild carpal tunnel syndrome (CTS). Single-fiber electromyography (SFEMG) measures the mean consecutive difference (MCD) as an expression of the variability in impulse transmission over the motor endplates and along the nerve fibers distally to the last branching point and along the muscle fibers. Application of concentric needle SFEMG in a group of CTS patients who showed pure sensory abnormalities in nerve conduction studies to examine for subclinical motor involvement. Methods Thirty CTS patients having only sensory involvement proved clinically and by conventional electrophysiological studies were included in addition to 30 control subjects. Concentric needle SFEMG was performed to the abductor pollicis brevis (APB), abductor digiti minimi (ADM), and extensor digitorum communis (EDC) muscles. Results There was a statistically significant difference in the MCD between the patient and control groups in the APB only ( p = 0.038). Conclusions The results suggest the presence of a subclinical motor median neuropathy at the wrist in patients with early and mild carpal tunnel syndrome and highlight the validity of the concentric needle SFEMG in early neuropathies. Trial registration PACTR201802002971380 registered 12 February 2018, retrospectively registered.