First described by Canadian neurologist and neurosurgeon Theodore Rasmussen and colleagues in 1958, Rasmussen syndrome (RS), also called Rasmussen encephalitis, is a rare, severe form of chronic childhood neuroinflammatory disease producing drug-resistant focal epilepsy, most often resulting in progressive hemiparesis. Most cases of RS occur in children between ages 3 and 15, though RS has also been seen in adults (~10%). The etiology of RS is unknown and thought to be sporadic.