Rasmussen's encephalitis

Rasmussen's encephalitis is a rare form of encephalitis caused by idiopathic inflammation of one hemisphere of the brain. It's characterized by frequent and severe seizures, loss of motor skills, loss of speech, and paralysis on one side of the body. 90% of cases occur in children under the age of 15 with an average age of 6. It strongly resembles epilepsy and is associated with it.
Treatment is to reduce the inflammation, usually with steroids. High dose steroids are used for acute cases, while low doses are more appropriate for chronic cases. Immunoglobulin and plasmapheresis are also used.
Rasmussen's encephalitis at Wikipedia