Rasmussen Encephalitis: An Update

Rasmussen encephalitis (RE) is a rare, devastating, progressive pediatric epilepsy. First described 60 years ago, RE continues to present challenges in diagnosis and management. RE causes a unilateral focal epilepsy in children that typically becomes medically refractory, results in significant hemiparesis, and causes progressive cognitive decline. The etiology is a cell-mediated immune attack on one cerebral hemisphere, though the inciting antigen remains unknown. While the underlying histopathology is unilateral and RE is described as "unihemispheric," studies have demonstrated (1) atrophy of the unaffected hemisphere, (2) electroencephalographic abnormalities (slowing and spikes) in the unaffected hemisphere, and (3) cognitive decline referable to the unaffected hemisphere. These secondary contralateral effects likely reflect the impact of uncontrolled epileptic activity (i.e., epileptic encephalopathy). Hemispheric disconnection (HD) renders 70 to 80% of patients seizure free. While it has the potential to limit the influence of seizures and abnormal electrical activity emanating from the pathological hemisphere, HD entails hemiparesis and hemianopia, as well as aphasia for patients with dominant HD. With the recent expansion of available immunomodulatory therapies, there has been interest in identifying an alternative to HD, though evidence for disease modification is limited to date. We review what is known and what remains unknown about RE.