Acute encephalopathy with 2009 pandemic flu: comparison with seasonal flu.

To clarify the features of acute encephalopathy associated with 2009 pandemic flu. We identified 51 patients with acute encephalopathy with seasonal flu from the data base accumulated by Tokai Pediatric Neurology Society. We also collected 10 patients with acute encephalopathy with 2009 pandemic flu. The clinical course, laboratory data, neuroimaging findings, treatment, and the outcome of these patients were recruited using a structured research form. These data were compared between the two groups. The age was larger in the 2009 pandemic flu group (median, 109.5months) than in the seasonal flu group (median, 44months). There was no significant difference in other demographic data, neurologic symptoms, laboratory and neuroimaging findings, and treatment. Various degrees of neurologic sequelae including death were observed in 32% of the patients in the seasonal flu group, and in 50% in the 2009 pandemic flu groups. The analyses of patients with ages of 6years or older revealed that moderate or more severe sequelae were more frequent in patients with 2009 pandemic flu. Acute encephalopathy with 2009 pandemic flu occurred mainly among children with 6years of age or older, and the outcome was worse in this age group compared with acute encephalopathy with seasonal flu.