Clinical Predictors of the Surgical Outcome of Severe Carpal Tunnel Syndrome : The Utility of Palmar Stimulation in a Nerve Conduction Study

Objective : Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy and can be effectively treated via surgery. However, the predictors for outcomes after surgery require further elucidation. CTS was diagnosed by nerve conduction study (NCS), and its severity was classified using a scale from 0 to 6 (Bland's classification). This study aimed to identify the utility of the palmar stimulation in a nerve conduction study in patients with severe CTS (Grades 5 and 6) and the relationship between Bland's grading score and the clinical outcome. Methods : A total of 67 patients (96 hands) diagnosed with CTS (Grade 3 and more) between April 2014 and April 2018 underwent surgery at our hospital, among which 33 patients (47 hands) were diagnosed with severe CTS (Grade 5 and 6) and were included in this study. NCS was performed initially and 6 months after the surgery, particularly focusing on the median palmar compound muscle action potential (CMAP) amplitude and the sensory nerve action potential (SNAP) amplitude ; furthermore, axonal degeneration was evaluated using the palmar CMAP/SNAP amplitudes. A simple questionnaire with a five-point rating scale was also administered 6 months after surgery, and improvements in the grading scale score were compared with the clinical outcome. Result : Among the 47 hands (85%), 40 demonstrated a significantly improved grading scale score (Grade 1 to 4 after surgery), while the remaining (7 hands, 15%) did not (Grade 5 or 6 after surgery). The palmar CMAP/SNAP amplitudes of the non-improvement group had reduced considerably or had disappeared completely compared with those of the improvement group (p＜0.05, Wilcoxon rank-sum test), and the five-point rating scale was poorer in the non-improvement group than in the improvement group. Conclusion : In this study, the median palmar CMAP/SNAP amplitudes were associated with axonal degeneration, with the most important factors being related to an improvement in the grading scale score and prediction of the clinical outcomes.