Reversible splenial lesion in influenza virus encephalopathy.

We describe a rare case of clinically mild, influenza-associated encephalopathy with a reversible splenial lesion. A 12-year-old Japanese girl presented with fever and headache, followed by muscle weakness and somnolence. Magnetic resonance imaging on day 4 of her illness showed a solitary lesion of the splenium of the corpus callosum that was most prominently visualized on diffusion-weighted images. The patient was diagnosed with influenza B-associated encephalopathy. Her neurologic signs had completely recovered by day 6, and the splenial abnormalities disappeared on day 11. A review of the literature identified four additional pediatric cases of this type of influenza-associated encephalopathy: three and one were caused by influenza A and B viruses, respectively. Common features include prompt and complete recovery from clinical and radiologic abnormalities, a relatively older age (> or = 5 years), and a higher incidence among the Japanese. To better understand the pathophysiology of this encephalopathy, we examined interleukin-6, tumor necrosis factor-alpha, and soluble tumor necrosis factor receptor 1 levels in serum and cerebrospinal fluid from this patient. The results did not reveal any elevations of these cytokines in the sera or cerebrospinal fluid, suggesting that this condition is not mediated by augmented cytokine responses.