A case of corpus callosum splenium encephalopathy and 2009 influenza A/H1N1

Encephalopathy with reversible lesion of the corpus callosum splenium has a favorable prognosis, but that in 2009 influenza A/H1N1 is unknown. We report a case of clinically mild encephalopathy with a reversible lesion of the corpus callosum splenium in which 2009 influenza A/H1N1 virus was confirmed by laboratory tests. A 15-year-old Japanese girl seen at the emergency unit for loss of consciousness 18 hours after fever onset had been diagnosed with influenza A, and administered zanamivir. Diffusion-weighted magnetic resonance imaging (MRI) indicated lesions of the corpus callosum splenium, and electroencephalography showed slow basic activity, suggesting influenza A related to encephalopathy. She required intensive care with ventilation for two days. Her consciousness had become normal by day 6 after onset, and MRI findings improved on day 7. She recovered without adverse sequelae.