A 23-year-old female with a known history of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) presented with 1 day of fever, reduced oral intake, and acute left-sided hemiparesis of 1-hour duration.

Plasma lactic acid was elevated to 6.7 umol/L. Plasma bicarbonate was 9 with an anion gap of 20. Brain MRI demonstrated multiple T2-hyperintense lesions in the bilateral frontal and parietal cortex and subcortical white matter, greater on the right side and in a nonvascular distribution ( Fig. 35.1 ).

MELAS. Brain MRI, axial FLAIR shows multifocal cortical and subcortical hyperintensities from stroke-like episodes ( arrows ). FLAIR , Fluid-attenuated inversion recovery; MELAS , mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes.

The differential diagnoses for acute stroke in a child are broad and include cardiac etiologies (e.g., congenital heart disease, valvular disease, arrhythmias), vasculopathies (e.g., dissection, inflammatory disorders), and prothrombotic conditions.

Metabolic stroke-like episodes can be seen in MELAS and, rarely, in Menkes disease and congenital disorders of glycosylation.

Arterial ischemic (vascular) stroke can be seen in homocystinurias, congenital disorders of glycosylation, cystinosis, and Fabry disease.

A focal cortical lesion could also be seen with infarction, infection, cortical dysplasia, and glioma.

In MELAS, lesions usually involve the cortex and subcortical white matter, particularly occipital and parietal lobes. Lesions involve nonvascular territories and can self-resolve or migrate over time. In the acute phase, there is a lactate peak on MRS and increased perfusion due to cerebral autoregulation in the setting of decreased mitochondrial oxygen extraction.

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes.