[MELAS syndrome masquerading as herpes encephalitis: genetic diagnosis]

MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke like episodes) is a mitochondrial disease related to the mitochondrial DNA mutation. The tRNALeu(UUR) mutation at the base pair 3234 is associated to 80% of cases of MELAS syndrome. The onset with the stroke like episodes is often before the age 40. Herpes simplex encephalitis (HSE) presents as acute episodes of focal neurologic deficit that are often related to the temporal lobe. Occasionally MELAS syndrome and HSE may have a similar clinical presentation.

A 33-year-old woman presented with seizures and a right parietotemporal syndrome of acute onset. The differential diagnosis between HSE and MELAS syndrome was established. MELAS syndrome was suspected based on her phenotype. The diagnosis of MELAS syndrome was confirmed by the presence of the mitochondrial tRNALeu(UUR) mutation at the base pair 3243.

The clinical presentation of the MELAS syndrome may mimic that of the HSE, and antiviral treatment should be given until the diagnosis of MELAS syndrome is definitive. The study of the mitochondrial DNA helps diagnosing in a non invasive way many patients with MELAS syndrome.