Sensory segmental latency values of the median nerve for a population of normal individuals

Seventy hands of 38 individuals without carpal tunnel syndrome (CTS) were compared with 54 hands of 30 age- and sex-matched patients with a clinical diagnosis of CTS. The comparison was performed in order to determine the limits for normal-usual values for sensory nerve conduction latency values of the median nerve in the area of the wrist, using the segmental stimulation technique in 1 cm increments described by Kimura. Kimura has recognized 0.5msec as the criterion for abnormality. In this study the segmental latency value of 0.4msec was also found to fall outside the range of normal-usual values. Although 0.5msec provides a higher degree of specificity (97%), its sensitivity is limited (54%). By contrast, 0.4msec provides an enhanced sensitivity (81%) while maintaining what we feel is an acceptable amount of specificity (81%). Although the predictive accuracy of 0.4msec (77%) is less than that of 0.5msec (93%), both values have merit in confirming CTS. With 0.5msec the clinician can be assured that relatively few normal individuals will be included in the CTS group; however, use of this value may result in a high number of false negative results. In contrast, 0.4msec affords the clinician the increased sensitivity needed to make a diagnosis of CTS in those cases where the conduction deficit is subtle and highly localized; but associated with its use is the possibility of false positive results. In both cases, a thorough history and clinical examination are necessary to ensure correct interpretation of the nerve conduction study results.(ABSTRACT TRUNCATED AT 250 WORDS)