Summary: Mitochondrial diseases are a group of rare diseases presenting with heterogeneous clinical, biochemical, and genetic disorders caused by mutations in the mitochondrial or nuclear genome. Multiple organs can be affected, particularly those with high energy demand. Diabetes is a common endocrine manifestation of mitochondrial diseases. The onset of mitochondrial diabetes can be latent or acute, and the presenting phenotype can be type 1- or type 2-like. Studies show that diabetes ais associated with latent progression of cognitive decline in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome. Herein, we report a case of rapid cognitive decline after the acute onset of diabetes in a patient with MELAS syndrome. The patient was a 36-year-old woman who was hospitalized due to hyperglycemic crisis and seizures. She was diagnosed with MELAS syndrome two years previously, and had gradually progressing dementia and hearing loss. However, following the acute onset of diabetes, she developed rapid cognitive decline and loss of ability to perform daily activities. In conclusion, the acute onset of diabetes could be an associated risk factor for rapid cognitive decline in patients with MELAS syndrome. Thus, these patients as well as healthy carriers with related genetic mutations should undergo diabetes education and screening tests. Moreover, clinicians should be aware of the possibility for acute onset of hyperglycemic crisis, particularly in the presence of triggering factors.
Learning points: Diabetes is a common endocrine manifestation of mitochondrial diseases, presenting with a type 1- or type 2-like phenotype depending on the level of insulinopenia. Metformin should be avoided in patients with mitochondrial diseases to prevent metformin-induced lactic acidosis. Mitochondrial diabetes can manifest before or after the onset of MELAS syndrome. In patients with MELAS syndrome, diabetes can initially manifest with a life-threatening severe hyperglycemic crisis and can cause rapid cognitive decline. Diabetes screening tests (e.g. hemoglobin A1c, oral glucose tolerance test, or random blood glucose level measurement) should be performed either systematically or in the presence of symptoms, particularly after triggering events. Genetic testing and counseling should be provided to patients and their families for the purpose of better understanding the inheritance, progression, and possible outcomes of the disease.