Diagnostic Utility of Medial Dorsal Cutaneous Sensory Response and the Medial Dorsal Cutaneous-To-Radial Amplitude Ratio (MDRAR) in Diabetic Polyneuropathy

Purpose: This study aimed to assess the diagnostic utility of the medial dorsal cutaneous (MDC) nerve and the medial dorsal cutaneous-to-radial amplitude ratio (MDRAR) in diabetic polyneuropathy (DP). Methods: Seventy-four patients clinically diagnosed with DP and 40 healthy controls underwent nerve conduction studies (NCS), including sural, radial, medial plantar (MP), and MDC sensory recordings. Most patients had recent-onset, mild-to-moderate DP. Sural-to-radial amplitude ratio (SRAR), medial plantar-to-radial amplitude ratio (MPRAR), and MDRAR were calculated. Minimal tibial F-wave latencies were height-corrected, and sural amplitudes were age-corrected. Diagnostic cut-off values were established by ROC analysis. Values below the cut-off, as well as absent responses, were classified as abnormal, and sensitivity and specificity were calculated. Results: A sural SNAP <6 µV demonstrated 42% sensitivity and 100% specificity. A minimal tibial F-wave latency ≥50 ms had 61% sensitivity and 100% specificity. For SRAR, a cut-off ≤0.40 yielded 49% sensitivity and 97% specificity; the 0.34 cut-off produced 38% sensitivity and 100% specificity, while the 0.21 cut-off yielded 19% sensitivity and 100% specificity. MPRAR and MDRAR demonstrated higher sensitivities (61 and 68%) but lower specificities (82 and 75%). Sural responses were obtainable in 82% of patients, whereas MP and MDC responses were recorded in 50 and 39%, respectively. Conclusions: MDRAR did not provide additional diagnostic value as a stand-alone electrophysiological parameter; however, bilateral absence of MDC responses emerged as a valuable marker of early distal involvement in DP. Further studies in selected patient groups are warranted to clarify the diagnostic contribution of MDRAR, particularly in early-stage and predominantly axonal forms of DP.