Background and Objectives: Padua (1997) and Bland (2000) have already proposed neurophysiological classification scales for patients with carpal tunnel syndrome (CTS), where the absence of orthodromic sensory response is used as a criterion of a severe stage. We hypothesized that antidromic values cannot be used equally for correct staging. Materials and Methods: We performed a consecutive investigation with nerve conduction studies in 60 arms of patients with CTS and prolonged distal motor latency. Results: In 11 out of 60 arms (18.3% of cases), orthodromic sensory nerve action potential (SNAP) was undetectable, while the antidromic SNAP was present. ROC curve analysis with Yoden index calculation were utilized in the study. The cut-off value of antidromic SNAP amplitude as a diagnostic marker of unrecordable orthodromic SNAP was 3.9 µV with high sensitivity and specificity. Conclusions: Our findings conflict with Padua et al.'s assertion that CTS staging can be determined irrespective of the stimulation technique. Antidromic SNAP amplitude is the most reliable parameter for predicting the absent orthodromic SNAP. Our study addresses the bias associated with the application of antidromic stimulation of median nerve sensory fibers for accurately staging moderate to severe CTS.
Keywords: antidromic and orthodromic stimulation; carpal tunnel syndrome; severe stage.
