Rasmussen's Encephalitis: Rasmussen's syndrome

Rasmussen's Encephalitis (RE) is a progressive inflammation of the part of the brain called the cerebral cortex, which is made up of a right and a left hemisphere. The disease starts at one site in one hemisphere and spreads to adjoining areas on the same side. Curiously, it does not spread to the other hemisphere. The inflammation leads to loss of nerve cells and scar formation and usually results in severe disability. Although RE is most often diagnosed in children under the age of ten years, it can also start in adolescence and adulthood. It is a rare disorder and probably affects 1 in 500,000 to 1,000,000.

The clinical problems in RE are determined by which areas of the affected hemisphere are inflamed as each area has different functions. As the disease spreads, more areas are damaged and the greater the severity and range of the disabilities. Typically, the disease progresses relentlessly until most of one hemisphere is affected. The inflammation burns out by itself but only rarely before severe disability has occurred. However, the speed of the spread varies between patients. At one end of the spectrum, the disease advances rapidly over a few weeks or months but at the other end, progression occurs slowly over several years. This slower clinical variant seems to be more common in adolescents and adults than in children. It is possible that there are milder forms of RE that fail to be recognized.

The typical clinical features of RE are epilepsy and neurological deficits such as hemiparesis (paralysis affecting one side of the body), hemianaesthesia (loss of touch-sense down one side of the body), visual loss, speech problems and cognitive deficits such as memory problems, intellectual impairment, and other neuropsychological deficits.

It is thought that in most patients RE is an autoimmune disorder. Many patients have antibodies in their blood that bind to nerve cells and are capable of damaging the brain. In most patients, it is not clear what triggers the abnormal immune response, although sometimes RE has followed an otherwise minor bacterial or viral infection, or head injury.

Surgery is the traditional treatment for advanced RE, and is used mainly to improve seizure control in patients with established disability. The extent of the surgery is determined by the severity, duration, rate of progression, the age of the patient and site of the disease. In patients with severe disease, all of the affected hemisphere may be removed (hemispherectomy). As epilepsy in RE is usually difficult to control, it can take time to find the best combination of anti-epileptic drugs. These drugs have no effect on progression of the underlying encephalitis.

There are now many reports that various combinations of powerful drugs that suppress the immune system (such as prednisolone, azathioprine, methotrexate, and cyclophosphamide) and therapies that modulate the function of the immune system (plasma exchange and intravenous immunoglobulin) may help at least some patients with RE. When more is known about the best use of immune therapy in RE, it is likely that fewer patients will need surgery.

Anti-viral drugs are only useful when the patient has a viral encephalitis rather than autoimmune RE.

Inheritance patterns
None.

Prenatal diagnosis
None.

Medical text written April 2002 by Dr Ian Hart, Senior Lecturer and Consultant Neurologist, University Department of Neurological Science, Walton Centre for Neurology and Neurosurgery, Liverpool, UK.

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Support and information for Rasmussen's Encephalitis is provided by the Encephalitis Support Group (see entry, Encephalitis)