Cerebral metabolism of oxygen and glucose in a patient with MELAS syndrome.

We studied cerebral oxygen and glucose metabolism as well as cerebral blood flow using positron emission tomography (PET) in a case with MELAS showing dementia, diabetes mellitus, ataxia and lactic acidosis without any signs of stroke. This case, confirmed to have a point mutation at position 3243 in the transfer RNA gene of mitochondrial DNA, developed a stroke-like episode 8 months after the PET study. Uncoupling was observed between cerebral oxygen metabolism and cerebral blood flow with reduced fractional oxygen extraction ratio, indicating hyperemia, not ischemia. The hyperemia may be closely related to the malfunction of mitochondria in aerobic energy production. A drastic decrease in cerebral oxygen metabolism (CMRO 2 ) was found globally in contrast to preserved cerebral glucose metabolism (CMR glu ), resulting in a remarkable decrease in the metabolic ratio (CMRO 2 /CMR glu ). The dissociation between cerebral glucose and oxygen metabolism may be characteristic of MELAS.