Background: Axonal polyneuropathy (APN) is a common kind of neurologic disorders, which is normally diagnosed by electrodiagnostic methods. Different muscles were studied to find a muscle, which can be considered as a reliable site for early diagnosis of mild APN; this muscle should be easily activated by patient, has the highest sensitivity to EMG changes of APN, and has the lowest rate of false positive results in normal subjects.
Materials and methods: Based on the inclusion and exclusion criteria, 32 patients were recruited, and all of them underwent needle EMG of 3 different muscles including Peroneus tertius (PT), tibialis posterior (TP), and dorsal interoseous pedis (DIP). EMG Findings of different muscles [Motor Unite Action Potential (MUAP) duration, MUAP amplitude, polyphasic MUAP, fibrillation potential (FP), and the ability of subjects to contract special muscle] were recorded and compared.
Results: Mean of MUAP amplitude was significantly different between all 3 muscles (P-values < 0.001). PT showed a significantly higher frequency of polyphasic MUAP than others (P-value: 0.001). The frequency of FP was significantly lower in TP than PT and DIP (P-values: 0.03 and 0.001, respectively). DIP showed significantly shorter MUAP duration than PT and TP (P-values 0.002 and 0.003, respectively). All cases were able to activate TP and PT voluntarily though only 20 patients could activate DIP (P-value < 0.0001).
Conclusion: The higher frequency of polyphasic MUAP, the higher frequency of FP, and finally, the ability of all patients in activation of PT voluntarily, all support the usefulness of PT for EMG studies in APN patients.
Keywords: Axonal polyneuropathy; dorsal interoseous pedis; electromyographic; peroneus tertius; tibialis posterior.