Teaching NeuroImages: A 48-year-old woman with MELAS

A 48-year-old woman with sensorineural hearing loss and diabetes presented with seizures and headache. She was thin and short-statured. Examination revealed encephalopathy, left homonymous hemianopia, and hemineglect. MRI showed slowed diffusion in right hemisphere, which did not follow a clear vascular distribution and without apparent diffusion coefficient correlate, inconsistent with infarction (figure 1).1 Magnetic resonance spectroscopy revealed inversion of lipid lactate peak (figure 2). She had elevated pyruvate but normal lactate. EMG demonstrated myopathy without denervation. Genetic testing showed m.3243A>G pathogenic variant of the MT-TL1 gene. This mutation is found in more than 80% of patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes and always coexists with wild-type DNA.2