sspe n a rare chronic progressive encephalitis caused by the measles virus and occurring primarily in children and young adults; death usually occurs within three years; characterized by primary measles infection before the age of two years Synonym(s) 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