Definition of Rasmussen syndrome

Rasmussen syndrome: A brain disorder caused by inflammation of brain cells in one hemisphere. Its cause is unknown. Rasmussen syndrome causes seizures often difficult or impossible to control with medication, and eventually results in brain shrinkage (atrophy). Treatment is with surgery, if possible. The inflammation seems to stop of its own accord eventually, but the damage done is irreversible.

It is also called Rasmussen encephalitis. There are frequent and severe seizures (convulsions), progressive loss of motor skills and speech, hemiparesis (paralysis on one side of the body), encephalitis (inflammation of the brain), dementia, and mental deterioration. The disorder affects a single brain hemisphere (one side or the other of the brain but not both sides) and generally occurs in children under the age of 15.

The standard treatment for Rasmussen's encephalitis is surgery to remove or disconnect the affected part of the brain (hemispherectomy). Anti-epileptic drugs are usually not effective in the long run in controlling the seizures. Alternative treatments may include plasmapheresis (the removal and reinfusion of blood plasma), ketogenic diet (high fat, low carbohydrate), and steroids (cortisone-like drugs).

The prognosis varies. Untreated, the disorder may lead to severe neurological deficits including mental retardation and paralysis. In some patients the surgery decreases the seizures. However, most patients are left with some paralysis and speech deficits.

Rasmussen's encephalitis is believed due to a number of causes. In some cases there is an abnormal immune attack against what is called the glutamate receptor GluR3. Antibodies directed against GluR3 have been identified in patients. (Reference: Rogers et al.: Autoantibodies to glutamate receptor GluR3 in Rasmussen's encephalitis. Science 265: 648-651, 1994.) Plasmapheresis (skimming off the blood plasma) has been tried (to remove the GluR3) but the improvement was short-lived.