Alternate-sided homonymous hemianopia as the solitary presentation of mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes syndrome.

Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome has various presentations. We report on a case of MELAS in which alternate-sided homonymous hemianopia was the main symptom of recurrent neurological defects. A 19-year-old woman suffered from blurred vision, headaches, vomiting, and fever that subsided within days. The ophthalmic examination demonstrated right homonymous hemianopia. One month later a similar episode occurred again. Computed tomography (CT) and magnetic resonance imaging (MRI) of her brain revealed an infarct in the left temporo-occipital lobes. Exercise tests showed lactic acidosis, and a muscle biopsy confirmed the diagnosis of mitochondrial myopathy. Half a month later, a third episode occurred. Visual field examination demonstrated left homonymous hemianopia and partial recovery of the right visual field. The infarct in the brain, as revealed by CT and MRI, was compatible with the visual field changes. MELAS should be ruled out in young patients who present with homonymous hemianopia accompanied by recurrent headaches or other recurrent symptoms.