Late-onset mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome with mitochondrial DNA 3243A>G mutation masquerading as autoimmune encephalitis:A case report

BACKGROUND Here,we present a unique case of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes(MELAS)syndrome,which initially appeared to be autoimmune encephalitis and was ultimately confirmed as MELAS with the mitochondrial DNA 3243A>G mutation.CASE SUMMARY A 58-year-old female presented with acute-onset speech impediment and auditory hallucinations,symmetrical bitemporal lobe abnormalities,clinical and laboratory findings,and a lack of relevant prodromal history,which suggested diagnosis of autoimmune encephalitis.Further work-up,in conjunction with the patient’s medical history,family history,and lactate peak on brain lesions on magnetic resonance imaging,suggested a mitochondrial disorder.Mitochondrial genome analysis revealed the m.3243A>G variant in the MT-TL1 gene,which led to a diagnosis of MELAS syndrome.CONCLUSION This case underscores the importance of considering MELAS as a potential cause of autoimmune encephalitis even if patients are over 40 years of age,as the symptoms and signs are atypical for MELAS syndrome.