Serial magnetic resonance imaging in post-infectious focal encephalitis due to influenza virus.

Two cases of a 13-year-old girl and a 14-year-old boy with postinfectious focal encephalitis due to influenza are reported. The clinical and magnetic resonance imaging (MRI) findings included: (1) partial motor seizures as the initial central nervous system manifestation, appearing more than 20 days after the influenzal infection, (2) no change in the level of consciousness although a boy demonstrated apraxia, and (3) high signal intensity lesions noticed with T2-weighted MRI located mainly in the cortex. The girl's lesion appeared to resolve within 10 days on MRI, while that of the boy (demonstrated in the thalamus on a third MRI) resolved within 1 week. However, a new lesion appeared in the cortex approximately 1 month later, that was visualized on a fourth MRI. Small gadolinium-enhanced lesions also were noticed during earlier stages in both patients. The pathogenesis of these MRI lesions is unknown, but the coexistence of small enhancing lesions, rapidly resolving lesions, and the elevated thrombin anti-thrombin III complexes, may indicate the presence of an angiopathy. Serial MRI examinations in patients with postinfectious encephalitis may lead to a better understanding of the pathogenesis of this disorder.