MELAS is a maternally inherited mitochondrial disorder, which usually has its onset during childhood. The stroke-like episodes have a predominantly posterior location, and patients' deficits are usually transient. In addition to stroke-like episodes and lactic acidosis, patients often have seizures, recurrent migraine like headaches with vomiting, hearing loss, short stature, and cognitive deficits. Chronic pancreatitis may be seen. While the muscle biopsy typically shows ragged red fibers, the myopathy rarely produces frank weakness.