The second lumbrical-interossei latency difference in carpal tunnel syndrome: Is it a mandatory or a dispensable test?

Objective: To assess the value of the 2L-INT latency difference in the electrodiagnosis of the carpal tunnel syndrome (CTS) and evaluate its sensitivity in comparison to other routine median motor and sensory studies. Methods: The study was conducted on 100 hands with symptoms and signs suggestive of CTS and 100 non-CTS hands as the control group. All were subjected to routine median motor nerve conduction study with stimulation at midpalm, wrist and elbow, median-versus-radial sensory comparison study and Second lumbrical-versus-interosseus (2L-INT) motor comparison study. Results: The results showed that the most sensitive tests were the median-radial sensory test and the 2LINT test and that both were correlated suggesting that the motor fibers of the median nerve can be compressed as early as sensory fibers. Conclusion: The 2L-INT test is as sensitive and important as the median-radial sensory test. Significance: We recommend the routine use of the 2L-INT test in clinically suspected cases of CTS especially in cases where routine median motor studies are normal together with the median-radial sensory test even if the sensory studies are normal. KEYWORDS: Carpal tunnel syndrome, Second lumbrical-interossei latency differenc