AANEM News Express

AANEM News Express

Science News: Electrophysiological Study of the Tibial Nerve Across the Tarsal Tunnel in Distal Symmetric Diabetic Polyneuropathy

Submitted by: Rebecca O'Bryan, MD
Edited by: Marcus Pai, MD, PhD

Mondelli M, Aretini A, Ginanneschi F. Electrophysiological study of the tibial nerve across the tarsal tunnel in distal symmetric diabetic polyneuropathy. Am J Phys Med Rehabil. 2022;101(2):152-159. doi:10.1097/PHM.0000000000001769

Summary: In this study, 124 consecutive patients with distal symmetric diabetic polyneuropathy diagnosed using the diabetic neuropathic index (DNI) were prospectively enrolled to investigate abnormalities of motor conduction in the tibial nerve across the tarsal tunnel. Tibial motor nerve conduction study (NCS) norms were developed based on 50 healthy volunteers in two age groups (18-59 and 60-80). They did not use a consistent side, but rather chose the side used for statistical analysis at random. Other NCSs were deep peroneal, medial plantar, and sural.

NCS values were considered abnormal if they differed at least 2 standard deviations above or below the means. The study reported slowing in the tibial nerve across the tarsal tunnel in 60.5% of patients, which exceeded abnormalities in sensory conductions in the sural and superficial peroneal nerves. However, in all patients, there was always at least one abnormal parameter of the sensory/mixed NCS (i.e., Distal sensory nerve conduction velocity and/or sensory nerve action potential amplitude/motor nerve action potential amplitude) of eight examined parameters.

Comments: This article seeks to demonstrate the importance of noting sites of entrapment in diabetic polyneuropathy patients as distinct and important parameters of diagnosis. However, in the discussion, the authors note the patients had no clear symptoms of tarsal tunnel syndrome. In addition, norms established in the implementation of this technique were developed in only 50 healthy controls, and the technique of recording conduction block or slowing across the tarsal tunnel is not one commonly implemented in most EDX labs. Their distances across the tarsal tunnel varied widely (65 to 90 mm), and this also can introduce measurement error and increase false positive/negative rates.

Overall, this is an interesting report, and certainly peripheral nerve entrapment in diabetic patients is an important issue. However, findings in otherwise clinically asymptomatic patients may not yield further advancement in treatment, and further normative data regarding this technique is needed.

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