Comparison of sural and distal sural nerve responses: Diagnostic role of the amplitude ratio in diabetic polyneuropathy.

OBJECTIVE

To assess the diagnostic utility of distal sural (DSUR) sensory responses and amplitude ratios compared with conventional proximal sural (PSUR) studies in diabetic polyneuropathy (DPN).

METHODS

Fifty-eight patients with diabetes and clinical evidence of polyneuropathy (neuropathic symptoms and/or signs, median Neuropathy Impairment Score of the Lower Limbs (NIS-LL) score 6 [IQR 2-8]) and 44 healthy controls underwent bilateral nerve conduction studies of the PSUR and DSUR, and the right radial nerve. Amplitudes, conduction velocities (CV), and amplitude ratios [sural-to-radial amplitude ratio (SRAR), distal sural-to-radial amplitude ratio (DSRAR), and proximal-to-distal sural amplitude ratio (PDSR)] were analysed.

RESULTS

PSUR and DSUR amplitudes were significantly lower and conduction velocities slower in patients compared with controls (p < 0.001). DSUR amplitude achieved diagnostic accuracy comparable to PSUR amplitude (AUC 0.762 vs. 0.775), with higher sensitivity (58.5% vs. 41.5 %) and preserved specificity (91 % vs. 93%). SRAR and DSRAR were reduced in patients, but their diagnostic performance was modest (AUC < 0.65). PDSR did not differ significantly between groups (p > 0.05) and was therefore not included in ROC analysis. Amplitude ratios showed weak correlations with diabetes duration, vibration threshold, and NIS-LL.

CONCLUSION

DSUR amplitude is a feasible and reliable parameter that increases sensitivity in the electrophysiological detection of DPN while maintaining high specificity. In contrast, PDSR did not provide significant diagnostic value, suggesting that absolute amplitude measures are more informative than ratio-based indices in routine clinical practice.