The role of cytotoxic T lymphocytes and other mechanisms in the pathogenesis of Rasmussen’s encephalitis (RE) is reviewed at the University of Vienna, Austria, and the University of Bonn, Germany. The densities of T cells, microglial nodules and glial fibrillary acidic protein positive astrocytes in surgically collected brain specimens are inversely correlated with disease duration. Inflammation and T cells are most pronounced at the earlier stages of RE. Brain specimens tested by immunochemistry and polymerase chain reaction for the presence of viruses such as enterovirus, Epstein Barr, cytomegalovirus and herpes simplex have failed to show a causal link between a specific virus and RE. Some patients with RE have high-titre anti-GLuR3 antibodies, and treatment with plasma exchange may result in a decrease in seizure frequency. However, anti-GLuR3 antibodies are not specific for RE, but may occur with noninflammatory focal epilepsy. The recent recognition of cytotoxicity by CD8/granzyme-B-positive T lymphocytes in brain biopsies or surgical specimens suggests that an autoimmune response mediated by cytotoxic T lymphocytes may be a key mechanism in the etiology of RE. 
COMMENT. Rasmussen’s encephalitis is characterized by intractable seizures of focal onset, usually an epilepsia partialis continua, and chronic inflammation with progressive hemispheric neurologic deterioration. In the final residual, atrophic stage of the disorder, seizures decrease in frequency and the neurologic deficit becomes static. The differentiation between a viral cause or an autoimmune mechanism remains to be determined.