Mononucleosis-associated subacute sclerosing panencephalitis.

A thirteen-year-old girl died of subacute sclerosing panencephalitis (SSPE) which occurred as part of a complex encephalitic illness related to acute infectious mononucleosis. The cerebrospinal fluid (CSF) Epstein-Barr virus (EBV) fluorescent antibody (FA) titer was 1:64. Electron microscopic examination revealed 17 nanometer (nm) diameter paramyxovirus-like nucleocapsids in brain sections and 90 nm diameter herpes virus-like enveloped particles in negatively stained brain tissue extracts. Indirect FA staining of cerebral cortex sections demonstrated both measles and EBV antigenic material. EBV antigenic material has not previously been demonstrated in brain tissue. The proportion of B lymphocytes among the patient's peripheral blood lymphocytes was significantly increased as compared to normal controls, while the T lymphocyte percentage was normal. It is suggested that defects in cellular immunity associated with infectious mononucleosis may have been responsible for activation of latent measles-like virus. This is the tenth reported case in which two viruses have been associated with SSPE. This is the third instance in the authors' experience in which acute EBV infection has occurred coincident with the development of SSPE.