Additional method for diagnosis of carpal tunnel syndrome: value of the second lumbrical-interossei test (2L-INT)

We examined 57 hands referred with suspected carpal tunnel syndrome (CTS) using the second lumbrical-interossei nerve test (2L-INT) as well as standard test. Sensory nerve conduction velocity (SCV) was detectible in 67% of patients (38/57), the abductor pollicis brevis-compound muscle action potential (APB-CMAP) in 84% (48/57), 2L-CMAP in 96% (55/57) and the first interossei palmares muscle (INT-CMAP) in 100% (57/57). ABP-CMAP was not recorded in patients in whom severe atrophy of the abductor pollicis brevis muscle was evident. As 2L-CMAP is maintained even in the most severe cases of CTS, the 2L-INT method is a valuable test for improving the accuracy of preoperative diagnosis in the electrophysiological diagnosis of CTS.