Utility of Dorsal Sural Nerve for Clinical Correlation and Detection of Early Diabetic Neuropathy.

Abstract

Background and objectives: Monofilament and tuning fork are commonly applied in clinical testing for distal sensory peripheral neuropathy (DSP). However, a dependable diagnosis of DSP requires nerve conduction studies (NCS). In the present study, we emphasize on the utility of dorsal sural sensory nerve action potential (dsSNAP) abnormality over sural sensory nerve action potential (SNAP) abnormality in detecting early DSP. Furthermore, we study the correlation between the clinical findings and sural SNAP and dsSNAP abnormalities.

Methods: The study included 101 persons with type 2 diabetes mellitus (T2DM) (PWD; 202 lower extremities [LEs]) aged 18-70 years, with the duration of T2DM being ≥6 months. Normative data was generated from controls (200 LEs). Clinical and electrophysiological findings of the study group were analyzed and discussed in comparison with the normative data. Furthermore, receiver operating characteristic (ROC) curve analysis determined the optimal cut-off for different sensory modalities, and Spearman's correlation tests were applied to analyze the correlation between NCS and clinical parameters.

Results: dsSNAP was abnormal in 39.1%, while sural SNAP was abnormal in 9.8% of asymptomatic PWD. Early neuropathy was detectable with subjective losses of 10% in temperature and pain sensations, 20% in touch sensation, and vibration duration <12 sec. Conventionally, the lower limit of normal of SNAP is considered as the cut-off for abnormality in the Electrophysiology (EP) lab. On ROC analysis, we found different optimal cut-offs for different sensory modalities.

Conclusions: Incorporating dorsal sural nerve into routine NCS enhances the detection of early DSP. Clinical sensory abnormalities, especially temperature and vibration sensation, showed the highest sensitivity and specificity, respectively, in relation to NCS abnormalities. Relying solely on standard institute-based reference SNAP amplitudes may potentially overlook early DSP.