Clinical Value of Magnetic Resonance Spectroscopy in the Initial Evaluation of Patients with Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-Like Episodes

Purpose: Magnetic resonance spectroscopy (MRS) is a diagnostic tool used to detect abnormal accumulation of lactate in the brain parenchyma in various metabolic diseases. This study evalu-ated the clinical roles of brain MRS in the initial assessment of mitochondrial encephalomyopa-thy, lactic acidosis, and stroke-like episodes (MELAS) caused by impairment of the mitochondrial respiratory chain. Methods: Twenty-five patients with the A3243G mutation among 34 MELAS patients referred to the pediatric neurology clinic of Gangnam Severance Hospital between January 2006 and De-cember 2020 were included. In this retrospective study, demographic, clinical, laboratory (serum lactate and lactate-to-pyruvate ratio), magnetic resonance imaging (MRI), and initial MRS (pres-ence of lactate peak and abnormal N-acetylaspartate [NAA]) data were reviewed. Results: Brain MRI showed cortical lesions in 24 of 25 genetically confirmed A3243G MELAS pa-tients with neurologic symptoms in this study. On MRS, 18 patients (72%) had increased lactate peaks, depicting anaerobic energy metabolism, and 17 patients (68%) had decreased NAA levels, indicating neuronal integrity. Ten patients underwent MRS in the acute stage (within 2 weeks of symptoms). Unlike patients who underwent MRS more than 2 weeks after symptom onset, a lac-tate peak on MRS was observed in all patients in the acute stage (P=0.011). Conclusion: Elevated lactate peaks in acute cerebral infarctions are highly suggestive of mito-chondrial encephalopathy. MRS alone is insufficient to diagnose MELAS, but it is valuable as a noninvasive supplemental diagnostic tool in combination with genetic testing.