Importance of Distinguishing Between Mitochondrial Encephalomyopathy With Elderly Onset of Stroke-Like Episodes and Cerebral Infarction.

The most common disease-causing mitochondrial DNA (mtDNA) mutation in mitochondrial encephalomyopathy (ME) with lactic acidosis and stroke-like episodes (MELAS) is m.3243A>G. In the future, the incidence of patients with cerebral infarction and diabetes mellitus is expected to increase tremendously. Additionally, the A3243G mutation typical of diabetes is estimated to be present in approximately 2% of all diabetes patients, which suggests that the potential disease population with a mitochondrial disorder is greater than previously thought, and there may have been many cases among the elderly that were misdiagnosed. Considering this background, MELAS with the onset of stroke-like episodes should be considered an important differential diagnosis for elderly patients with cerebral infarction, although it might have been overlooked until now. A 68-year-old Japanese female developed convulsive seizures and was admitted to Hospital of International University of Health and Welfare for epilepsy. She had been hospitalized twice in the previous year for cerebral infarction and seizures. She experienced sensorineural hearing loss at a young age. Thus, although she was elderly, we suspected MELAS and detected elevations of pyruvic and lactic acid. A genetic test revealed a point mutation in the mtDNA (m.3243A>G) that led to a definitive diagnosis of MELAS. To date, MELAS has been regarded as a disease of the relatively young. The incidence of patients with cerebral infarction and diabetes mellitus is expected to greatly increase. Thus, we should evaluate cerebral infarction in the elderly with caution to prevent missed diagnoses of MELAS.