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

ObjectiveTo 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.MethodsThe 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.ResultsThe 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.ConclusionThe 2L-INT test is as sensitive and important as the median-radial sensory test.SignificanceWe 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.