Exploring Neuropathy and Myopathy in Mitochondrial Diseases: Insights from Nerve Conduction Studies and Electromyography

Objective: Mitochondrial diseases (MDs) are characterized by significant genetic and clinical heterogeneity. Although they are frequently investigated for potential central nervous system involvement, they can also affect the peripheral nervous system, leading to neuropathy and myopathy. The aim of this study is to determine the role of nerve conduction study (NCS) and electromyography (EMG) in the diagnosis of MD and the monitoring of peripheral nervous system involvement in patients with MD. Method: This retrospective study examined data from 25 patients with MD. Clinical and laboratory parameters were compared between groups with and without abnormal electrophysiological findings. Additionally, subtypes of neuropathy were classified, and correlations between genotypes and phenotypes were analyzed. Results: Neuropathy was detected at a considerable rate of 40%. The findings were predominantly consistent with the expected axonal neuropathy in MD, particularly in cases with lower limb-onset MD, although demyelinating patterns were also frequently observed. Notably, neuropathy was more prevalent in patients with mitochondrial variants than previously reported. Furthermore, physical examination findings and motor symptoms failed to predict neuropathy. Similarly, myopathic findings identified on EMG were observed even in cases without corresponding neuropathy-specific physical examination findings, motor symptoms, or elevated muscle enzyme levels. Conclusions: The routine use of NCS and EMG serves as a valuable guide in the diagnostic process of MD. They are considered important tools for both diagnostic evaluation and ongoing monitoring of peripheral nervous system involvement.