What is Acute Disseminated Encephalitis?

Acute disseminated encephalitis, also called acute disseminated encephalomyelitis (ADEM), is an autoimmune inflammatory condition that involves the white matter of the brain and the spinal cord. This means that the body’s own immune cells attack and destroy the myelin sheath of the nerves, resulting in neurological symptoms similar to that of multiple sclerosis. In contrast to other types of encephalitis, such as multiphasic or recurrent disseminated encephalomyelitis which have multiple demyelinating episodes, the demyelination in ADEM only occurs once. Acute disseminated encephalitis can have viral, parasitic, or bacterial causes, but it may also occur in a spontaneous manner. Treating the condition generally involves the use of anti-inflammatory agents and provision of symptomatic relief.

The different causes of acute disseminated encephalitis include various infections or immunizations. Some of the most commonly suspected viral causes are the Epstein-Barr virus, herpes simplex virus, and cytomegalovirus. Other viruses that are implicated include influenza, enterovirus, varicella, mumps, rubella, hepatitis A, and coxsackievirus. Bacterial infections include beta-hemolytic Streptococci, Leptospira, Mycoplasma pneumoniae, and Borrelia burgdorferi. The Semple rabies vaccine has been proven to induce ADEM, but vaccination with hepatitis B, polio, pertussis, diphtheria, pneumococcus, measles, varicella, mumps, rubella, influenza, and Japanese encephalitis may also lead to ADEM.

Symptoms of acute disseminated encephalitis usually occur with one to three weeks after the initial viral gastrointestinal or respiratory symptoms. The most prominent symptoms of ADEM include fever, headache, and neurological abnormalities such as irritability, drowsiness, seizures, weakness or paresis, and sometimes coma. Other symptoms include cranial nerve palsies, hallucinations, language disturbance, blindness, vomiting, and psychiatric abnormalities. These symptoms occur abruptly, but they may also develop over a few days. The average time from onset to the peak of symptom severity is approximately five days.

Treatment involves the aggressive use of anti-inflammatory agents, such as corticosteroids, to reduce the inflammation of the central nervous system and to improve symptoms. Physicians would usually administer high doses of methylprednisolone or dexamethasone intravenously, followed by oral prednisolone in the succeeding three to six weeks. When these drugs are not effective or when the patient cannot take them, high-dose intravenous immunoglobulin (IVIG) is administered as an alternative. Other alternative treatments include plasmapheresis, cyclophosphamide, and mitoxantrone.

Cases of ADEM usually recover within one to six months after onset, and affected children tend to recover spontaneously. Poorer outcomes are seen in ADEM patients who do not respond to corticosteroids, have severe neurological abnormalities, or have sudden onset of symptoms. Approximately 5% of affected patients die of this condition. Among survivors, complications of acute disseminated encephalitis may occur. The complications are usually affectations of motor function that include mild clumsiness, hemiparesis or weakness of one side of the body, and ataxia or uncontrolled body movements.