Teaching NeuroImages: diffuse posterior leukoencephalopathy in MELAS without stroke-like episodes.

Dimitri Renard, MD Helene Bonnaure, MD Pierre Labauge, MD, PhD A 46-year-old woman with a history of seizures, migraine, diabetes mellitus, and neurosensory hearing loss presented with progressive gait unsteadiness. Her mother had the same clinical features. Examination revealed short stature, cognitive deficit, and ataxia. Brain MRI showed diffuse atrophy and posterior leukoencephalopathy (figure). Lactate levels were slightly elevated in both serum and CSF. Mitochondrial DNA analysis revealed the m.3243A G tRNALeu(UUR) mutation that causes mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Brain MRI in MELAS classically shows lesions that predominantly affect the occipital cortex and do not conform to large-vessel territories. The posterior predominance of brain lesions in our patient, although nonspecific, suggested a MELASassociated pathology. Diffuse symmetric leukoencephalopathy in patients with the m3243A G mutation and lacking stroke-like episodes is extremely rare and their pathophysiology is unclear.1,2 Diabetes mellitus might also play a role in these radiologic abnormalities.