Paramyxovirus-like particles associated with acute demyelination in chronic relapsing multiple sclerosis.

Electron microscopy of small perivenous demyelinating lesions in a formalin-fixed brain of a multiple sclerosis subject revealed nuclear and cytoplasmic particles resembling paramyxovirus nucleocapsids. These particles, 18 to 20 nanometers in diameter, were found in mononuclear cells related to the central vein and infiltrating the zone of active demyelination. It is suggested that multiple sclerosis lesions may be initiated by seeding of lymphocytes bearing latent paramyxovirus to white matter of the central nervous system.