1. (noun)subacute sclerosing panencephalitis, SSPE, inclusion body encephalitis, subacute inclusion body encephalitis, sclerosing leukoencephalitis, subacute sclerosing leukoencephalitis, Bosin's disease, Dawson's encephalitis, Van Bogaert encephalitis a rare chronic progressiveencephalitis caused by the measlesvirus and occurring primarily in children and young adults; death usually occurs within three years; characterized by primarymeaslesinfection before the age of two years