Influenza-associated acute encephalopathy in Japanese children in 1994-2002.

We addressed the incidence of influenza-associated acute encephalopathy, which is distinct from Reye syndrome, in children in Japan. Eighty-nine children with a mean age of 3.8 years were reported to have developed this disease during eight influenza seasons (December 1994-April 2002) in Hokkaido, Japan. None of them had received aspirin. Most of the patients rapidly became comatose with or without convulsions with a mean interval of 1.7 days from the onset of fever to the onset of central nervous system symptoms. Thirty-three (37.1%) patients died and 17 (19.1%) patients had neurological sequelae. A total of 53 (59.6%) cases were proved to have an influenza virus infection. Interleukin-6 and tumor necrosis factor-alpha were markedly elevated in serum and cerebrospinal fluid samples from two patients who died after a rapid, fulminant course. A post-mortem examination of one fatal case revealed vasogenic brain edema with generalized vasculopathy, suggesting that the generalized impairment of vascular endothelial cells caused by highly activated cytokines plays a central role in the pathophysiology of this disease. We conclude that influenza-associated acute encephalopathy may be an underestimated syndrome and is another reason to promote vaccination against influenza in infants and younger children.