Reversible splenial lesion associated with novel influenza A (H1N1) viral infection.

We describe clinically mild encephalopathy with a reversible lesion in the splenium of the corpus callosum associated with the novel swine-origin influenza A (H1N1) virus. A 14-year-old Japanese boy was hospitalized because of dysarthria and dysphagia 5 days after the onset of fever. He had been receiving zanamivir for 4 days before admission. Diffusion-weighted magnetic resonance imaging on clinical day 6 revealed lesions in the splenium of the corpus callosum and bilateral frontoparietal white matter. With continued zanamivir treatment, his signs completely resolved within 24 hours, and the abnormal radiologic signals resolved 3 days later. Neurologic signs were limited to pseudobulbar palsy, without impairment of consciousness or seizures. This presentation is, to our knowledge, the first among patients with mild encephalopathy with a reversible lesion in the splenium of the corpus callosum, expanding the clinical spectrum of this condition. Our findings indicate that pandemic 2009 influenza A (H1N1) infection can cause mild encephalopathy with a reversible lesion in the splenium of the corpus callosum.