Assessing the severity of carpal tunnel syndrome during physical examination by measuring two-point discrimination: Post-hoc analysis of prospectively collected data.

Introduction: Carpal tunnel syndrome (CTS) commonly presents after distal radius fractures. Assessing its degree of severity is essential to therapeutic decision-making - i.e. operative vs. conservative treatment. The role of the two-point discrimination (2PD) has not yet been evaluated as a potential indicator of severity during physical examination. Therefore, in our cross-sectional study, we aimed to find a correlation between 2PD values and disease severity, based on the gold-standard electromyography and electroneurography (EMG-ENG) and ultrasonography findings.

Methods: We conducted a post-hoc analysis of prospectively assessed CTS patients for 2PD values. We analyzed the correlation between 2PD and EMG-ENG measurement results, patient characteristics, nerve ultrasonography, and relevant CTS questionnaires. CTS severity was determined by EMG-ENG results. The Pearson correlation was calculated between variables.

Results: The study included 81 patients. The three pre-determined EMG-ENG severity categories showed a significant correlation between both 2PD values and 2PD severity categories (r= 0.29 [0.07-0.48] and r= 0.26 [0.03-0.45]). Distal sensory latency and conduction velocity values correlated significantly with 2PD categories. However, the correlation coefficients (r= 0.25 [0.02-0.46] and r=-0.24 [-0.37-0.07]) were low. The 2PD severity categories showed no significant correlation with the severity assessed by nerve ultrasound (r=-0.07 [-0.38-0.25]). The 2PD values showed a significant correlation between the values of the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire (r= 0.3 [0.06-0.51]). We concluded that the best cut-off value for differentiating severe from non-severe CTS was at the 9.5 mm 2PD cut-off value (sensitivity = 0.65 [0.45-0.81], specificity = 0.71[0.58-0.82], AUC = 0.71 [0.59-0.83]).

Conclusion: There is a significant correlation between 2PD values and the severity of carpal tunnel syndrome as determined by EMG-ENG; however, they are not interchangeable. Based on the results of our study, we propose that measuring two-point discrimination may be a quick and easy, reliable and cost-effective screening method to assess the severity of carpal tunnel syndrome following distal radius fractures.