CEREBRAL HYPEREMIA IN MELAS

Background The pathophysiology of strokelike episodes in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes) is uncertain. Case Description We studied a 24-year-old man with MELAS who had fluent aphasia and right hemianopia. Magnetic resonance imaging and computed tomography showed a large infarction in the parietal, temporal, and occipital lobes. We performed serial planar Xe-133 regional cerebral blood flow studies and single-photon emission computed tomography. Fifteen and 26 days after the strokelike episode, there was generalized hyperperfusion, highest in infarcted areas. Four and 8 months after the strokelike episode, the brain was still hyperemic, with highest flow in noninfarcted tissue. Reactivity to CO2 was less than normal within the infarct at 26 days but improved thereafter. In the noninfarcted region, vasomotor reactivity was impaired at 4 months, when resting flows were at their peak. Conclusions We observed generalized cerebral hyperemia and fluctuating CO2 reactivity in MELAS, possibly a consequence of local lactic acid production. In addition, this case suggests that nonquantitative functional imaging may be misleading in MELAS.