Metformin induces stroke-like episodes in a patient with mitochondrial disease

Abstract

A 48-year-old woman was admitted to our hospital with motor aphasia, right homonymous hemianopia, and right-sided hemispatial neglect. Her mother and maternal grandmother had a history of deafness and diabetes mellitus. Five years earlier, she was diagnosed with diabetes mellitus. Metformin treatment was started at 6 months before admission, and the metformin dose was increased. From this period, she became aware of hearing difficulties. On day X, she was admitted to another hospital due to motor aphasia, and she was treated for a diagnosis of herpes encephalitis and then discharged on day X + 15. The next day, she was admitted to our department. Brain magnetic resonance imaging showed lesions in the left temporal, occipital, and parietal lobes. Magnetic resonance spectroscopy showed a lactate peak in the lesions. Serum and cerebrospinal fluid showed elevated lactic acid and pyruvic acid levels; the lactate/pyruvate ratio was also elevated. She was diagnosed with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). In this case, hearing difficulty and stroke-like episodes occurred after metformin use, which worsened mitochondrial disease by elevating lactate levels. In patients with maternal inheritance of antibody-negative type 1 diabetes mellitus, hearing loss, short stature, and so forth, lactate or pyruvic acid levels should be measured to assess the possibility of mitochondrial disease.