Second lumbrical and interossei latency difference in Carpal Tunnel Syndrome

Objective To evaluate the diagnostic value of second lumbrical and interossei distal motor latency difference (2LIDMLD) in diagnosing CTS of different electro-physiological grades of CTS. Methods 2LIDMLD was standardized in 120 hands of healthy controls. Subjects with clinically diagnosed CTS and CTS with incidental polyneuropathy were prospectively evaluated with 2LIDMLD in addition to other standard diagnostic tests. Sensitivities of these tests were compared in patients with CTS of varying grades of severity and CTS associated with polyneuropathy. Results Two hundred and fifty hands of 130 patients met the clinical criteria for CTS. Sensitivity and specificity of 2LIDMLD, palm–wrist distal sensory latency difference (PWDSLD), and median distal motor latency (MDML) were 85.60% and 96.67%, 68.80% and 96.10%, 60.80% and 97%, respectively. Sensitivity of 2LIDMLD in mild CTS was similar to that of PWDSLD. In severe CTS, and CTS with polyneuropathy, 2LIDMLD was the most sensitive test. It was the only test of localizing value in 16% of hands with severe CTS, when all other methods failed due to absent median motor and sensory responses. Conclusions 2LIDMLD is a sensitive, specific for diagnosis of all grades of CTS. It is an accurate and reliable method that helps especially in diagnosis of severe CTS and CTS associated with polyneuropathy, when other standard localized tests fail. Significance The second lumbrical is relatively less affected in severe carpal tunnel syndrome and median to ulnar comparison, using 2LIDMLD, appears to be a reliable and a valuable technique in the localization of severe CTS and CTS associated with polyneuropathy, especially when the median sensory or motor responses are absent on routine conduction studies.