Do the amplitude ratios of sensory nerve action potentials in the lower extremities have any diagnostic utility in distal diabetic polyneuropathy?

Background/aim: To investigate the diagnostic sensitivity of sural sensory nerve action potential (SNAP) to medial femoral cutaneous nerve and dorsal sural to sural SNAP amplitude ratios in patients with diabetic polyneuropathy.

Materials and methods: Sural/radial (SRAR), sural/medial femoral cutaneous (SMFAR), and dorsal sural/sural (DSSAR) SNAP amplitude ratios were calculated in 22 controls and 46 patients with type 2 diabetes mellitus. Combined sensory scores (superficial peroneal, sural, dorsal sural, and medial plantar SNAPs), and amplitude ratio scores (SRAR, DSSAR, and SMFAR) were assessed. The parameters were compared statistically between the patient and control groups.

Results: All SNAP amplitudes were significantly lower in patients as compared with those of the controls. Reduced medial plantar SNAP amplitude was the most frequent abnormality in the patient group. DSSAR and SMFAR, but not SRAR were found to have significant value in differentiating patients from controls with low sensitivity and moderate specificity. The combined sensory score improved the diagnostic accuracy for diabetic polyneuropathy, while the other combined scores add no additional value in this respect.

Conclusion: Distal nerve conduction studies (NCSs) are most useful in diagnosing mild diabetic polyneuropathy. Although DSSAR and SMFAR can be moderately sensitive alternatives, particularly when used in combined scores, these ratios do not add any diagnostic value in patients with axonal polyneuropathies of similar severity.