Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome mimicking herpes simplex encephalitis on imaging studies.

We present a case in which mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome mimicked the clinical and radiological signs of herpes simplex encephalitis. In a patient with subacute encephalopathy, on computed tomography and magnetic resonance imaging, lesions were present in both temporal lobes extending to both insular regions with sparing of the lentiform nuclei and in both posterior straight and cingulate gyri. Final diagnosis of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome was based on biochemical investigations on cerebrospinal fluid, electromyogram, muscle biopsy, and genetic analysis. On diffusion-weighted imaging, diffusion restriction was present in some parts of the lesions but not throughout the entire lesions. We suggest that this could be an important sign in the differential diagnosis with herpes simplex encephalitis.