Epidemiological changes of acute encephalopathy in Japan based on national surveillance for 2014-2017

Abstract Background We previously reported the nationwide, epidemiological data of acute encephalopathy in Japan during 2007-2010. Here we conducted the second national survey of acute encephalopathy during 2014-2017, and compared the results between the two studies to elucidate the trends in the seven years’ interval as well as the influence of changes in pediatric viral infections and guidelines for acute encephalopathy in Japan. Methods The Research Committee on Acute Encephalopathy supported by the Japanese Government sent a questionnaire to 507 hospitals throughout Japan, and collected the responses by mail. Results A total of 1115 cases from 267 hospitals reportedly had acute encephalopathy during April 2014–June 2017. In this study, the age at onset was younger, the ratios of recently established syndromes, such as acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) and clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS), were higher, and the ratio of influenza-associated encephalopathy was lower, than in the previous study. The age at onset of influenza-associated encephalopathy was lower, and that of HHV-6/7-associated encephalopathy higher, compared to the first survey. The outcomes of entire acute encephalopathy remained unchanged. Conclusion Some of these changes reflected the recent trends of viral infectious diseases including 2009 influenza pandemic, and others the standardization of the diagnosis of acute encephalopathy in Japan.