Region-specific Sudoscan electrochemical skin conductance and clinical correlates in electromyography-confirmed radiculopathy: a cross-sectional study

Background Sudoscan measures electrochemical skin conductance (ESC) at the hands and feet, but its role in focal radiculopathy is uncertain. We evaluated region-appropriate ESC in patients with electromyography/nerve conduction study (EMG/NCS)-confirmed radiculopathy, focusing on values below device-defined thresholds displayed on the Impeto Medical SUDOSCAN result page that might indicate coexisting distal sudomotor dysfunction rather than radiculopathy itself. Methods This cross-sectional study included 177 participants contributing 200 EMG/NCS-confirmed radiculopathy-region observations; 23 participants contributed both upper- and lower-region observations. Sudoscan and EMG/NCS were performed concurrently. For unilateral radiculopathy, affected-side hand ESC (upper region) or foot ESC (lower region) was used; for bilateral radiculopathy, left and right values were averaged. Below-threshold ESC was defined using device-defined boundaries of < 60 µS for hands and < 70 µS for feet. These boundaries were not derived or validated for radiculopathy. Regression used participant-clustered robust standard errors. Results Mean region-specific ESC was 63.2 ± 15.9 µS overall, 51.9 ± 15.1 µS for upper-region observations, and 68.1 ± 13.6 µS for lower-region observations. ESC was below the limb-specific threshold in 108/200 observations (54.0%; participant-clustered 95% CI 46.5–61.5%) and in at least one region in 99/177 participants (55.9%; 95% CI 48.6–63.0%). Rates were 70.5% for upper and 46.8% for lower observations. In the multivariable model (170 observations from 154 participants), older age (adjusted β = −0.29 µS/year, 95% CI − 0.51 to − 0.08; p = 0.007) and upper/hand measurement (adjusted β = −16.50 µS vs. lower/foot, 95% CI − 20.86 to − 12.14; p < 0.001) were associated with lower ESC. Among 51 unilateral observations from 50 participants, affected-side ESC was 1.78 µS lower than contralateral ESC (participant-clustered 95% CI − 3.16 to − 0.41; exploratory p = 0.012). Conclusions ESC was below the device-defined limb-specific threshold displayed on the Impeto Medical SUDOSCAN result page in 54.0% of EMG/NCS-confirmed radiculopathy-region observations. The upper–lower difference cannot be separated from the inherent hand–foot measurement-site difference. These findings do not support Sudoscan for diagnosing or localizing radiculopathy. Any adjunctive role in identifying coexisting distal sudomotor dysfunction remains hypothesis-generating and requires prospective validation.