The Usefulness of Muscle Biopsy in Initial Diagnostic Evaluation of Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes

Purpose: The disease entity mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is characterized by an early onset of stroke-like episodes. MELAS is the most dominant subtype of mitochondrial disease. Molecular genetic testing is important in the diagnosis of MELAS. The mitochondrial DNA (mtDNA) 3243A>G mutation is found in 80% of MELAS patients. Nevertheless, molecular analysis alone may be insufficient to diagnose MELAS because of mtDNA heteroplasmy. This study aimed to evaluate whether muscle biopsy is useful in MELAS patients as an initial diagnostic evaluation method. Materials and Methods: The medical records of patients who were diagnosed with MELAS at the Department of Pediatrics of Gangnam Severance Hospital between January 2006 and January 2017 were reviewed. The study population included 12 patients. They were divided into two subgroups according to whether the results of muscle pathology were in accordance with mitochondrial diseases. Clinical variables, diagnostic evaluations, and clinical outcomes were compared between the two groups. Results: Of the 12 patients, seven were muscle pathology-positive for mitochondrial disease. No statistically significant difference in clinical data was observed between the groups that were muscle pathology-positive and muscle pathology-negative for mtDNA 3243A>G mutation. Additionally, the patients with weakness as the initial symptom were all muscle pathology-positive. Conclusion: The usefulness of muscle biopsy appears to be limited to an initial confirmative diagnostic evaluation of MELAS. Muscle biopsy can provide some information in MELAS patients with weakness not confirmed by genetic testing.