Unusual intranuclear filaments in the circulating lymphocytes of patients with multiple sclerosis and optic neuritis.

Mononuclear cells obtained from the peripheral blood of patients with multiple sclerosis (MS) and optic neuritis (ON) were examined by electron microscopy. Unusual intranuclear filaments identical with the so-called paramyxovirus-like filaments were found in circulating lymphocytes from 5 patients with MS and 3 with ON. They were observed in 0.1 to 0.5% of the mononuclear cells. Electron microscopy of the blood cells from 5 other patients with ON, 3 patients with neurologic diseases other than MS, and 4 normal subjects failed to reveal similar structures. The filaments were also absent from blood cells from blood cells from normal subjects during the process of autolysis.