Rasmussen's Encephalitis Health Article

Definition

Rasmussen's encephalitis, also termed Rasmussen's syndrome, is a rare degenerative brain disease that initially affects only one side of the brain. It first manifests in childhood with the onset of epileptic seizures. Later, it progresses to paralysis of one side of the body (hemiparesis), blindness in one eye (hemianopsia), and loss of mental function. The seizures in Rasmussen's encephalitis usually resist therapy with anticonvulsant drugs, but respond well to hemispherectomy, the surgical removal of the entire affected side of the brain.

Description

Rasmussen's encephalitis usually appears in children, but may also strike in adulthood. It initially affects only one side (hemisphere) of the brain. The disease causes uncontrollable seizures and other symptoms that become progressively worse. The affected hemisphere shows changes characteristic of chronic inflammation, including long-term atrophy or shrinkage, hence, the term encephalitis (inflammation of the brain). Unless the affected hemisphere is removed, the disorder eventually spreads to the brain's other hemisphere.

Demographics

Rasmussen's encephalitis is very rare; between 1958, when the syndrome was first identified, and 2000, barely 100 cases were identified. The medical literature does not describe a higher incidence of this disease in either gender or in any particular racial group or geographical area.

Causes and symptoms

For many years, the cause of Rasmussen's encephalitis was a mystery. It seemed to resemble a viral infection, but despite much research, no organism could be consistently found in the brains of those who had suffered from the disorder. Finally, in the early 1990s, it was discovered that Rasmussen's encephalitis is an autoimmune disease, that is, a disorder in which the body is attacked by its own immune system.

Specifically, the body responds to one of the glutamate receptors, GluR3, as if it were an invading organism. Glutamate is a neurotransmitter, or one of the chemicals that neurons use to signal to each other. A receptor is a complex molecule embedded in the cell membrane of a neuron that detects the presence of a specific neurotransmitter and responds by causing some change in the neuron itself, such as admitting a flow of sodium, potassium, or calcium ions into the cell. There are at least 20 distinct receptors for glutamate in the brain, one of which is denoted GluR3. In Rasmussen's encephalitis, the body (for reasons still unknown) produces anti-GluR3 antibodies. Attracted by these antibodies, groupings of special immune system proteins, termed complement, gather on neurons in the affected parts of the brain, eventually forming "membrane attack complexes" that damage the neurons. It is not known why this autoimmune response attacks only one side of the brain at first, but it was hypothesized that a breach in the blood-brain barrier in one part of the brain might allow initial access of antibodies to neurons. The arrival of lymphocytes in the affected area, with consequent swelling of tissues, may then cause further damage to the blood-brain barrier and allow more anti-GluR3 antibodies access to the neurons. Finally, it remains possible that infection by cytomegalovirus may play a role in triggering the autoimmune processes of Rasmussen's encephalitis. Cytomegalovirus DNA has been detected in the brains of some patients.

The first symptom of Rasmussen's encephalitis is seizures, usually beginning suddenly before the age of 10. Loss of control over voluntary movements, loss of speech ability (aphasia), hemiparesis (weakness on one side of the body), dementia, mental retardation, and eventually, death, will follow if untreated.