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Acute disseminated encephalomyelitis, or ADEM, is an inflammatory neurological disease, similar to the autoimmune disease Multiple Sclerosis. But first, what do all those words actually mean? In medical terminology, acute means the disease has a rapid onset and is not a chronic, or reoccurring, disease. Disseminated means that it affects multiple areas in the nervous system. Finally, encephalomyelitis means inflammation of the brain and spinal cord; as opposed to encephalitis, which is inflammation of the brain.
ADEM is one of many inflammatory conditions that cause degeneration of the myelin that protects the nerves in our brain and spinal cord. Without myelin, nerves cannot transmit signals correctly and results in a loss of function in the damaged nerves. This disease accounts for one third of all cases of encephalitis and was initially described over 250 years ago!
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Although the exact cause of acute disseminated encephalomyelitis is unknown, it often appears after a viral infection or, occasionally, after an MMR vaccination.** Additionally, it seems as though there may be a genetic predisposition to the disease as well. Although not as likely, ADEM can also occur after trauma or with no known incident before onset. It is more likely to occur in children, but adults can develop symptoms of the disease as well.
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Signs and Symptoms
The symptoms of acute disseminated encephalomyelitis occur rapidly and usually lasts for a few weeks to a month, although it can be longer. The illness is first noticed by signs of encephalitis, which include fever, tiredness, headache, stiff neck, nausea and vomiting. These initial symptoms are closely followed by neurological disruptions, such as confusion and clumsiness. In severe cases seizures, paralysis of one or both sides, loss of vision, and coma can also occur. ADEM usually occurs as a single episode with partial or complete recovery after symptoms wane; however, a few patients have a second attack and a small number may develop multiple sclerosis.
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ADEM is usually diagnosed by examining the patient's medical history and what happened immediately preceding symptoms, like any medications, infections, or other anomalies that may have occurred. A physical and neurological examination help confirm the patient's claims and an MRI (magnetic resonance imaging) can be used to search for areas of damage in the brain or spinal cord. Importantly, looking for old versus new areas of damage can help pinpoint whether the symptoms correspond to ADEM or to an undiagnosed case of multiple sclerosis. In addition, a lumbar puncture to look at cerebrospinal fluid often shows that there are increased amounts of immune proteins and cells, which indicates immune system activation.
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Unfortunately, there are no specific treatments available for acute disseminated encephalomyelitis. Anti-inflammatory drugs are used to suppress the inflammation in the central nervous system and help inhibit any further damage to the myelin under attack. Most people respond well to intravenous corticosteroids and a few patients need plasmapheresis or immunoglobulin therapy in addition to the corticosteroids. Any other treatment is merely to control the symptoms, like pain management for headaches or anti-nausea medication for nausea and vomiting.
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Treatment usually can shorten the duration of the illness and stop further progression of the disease, so early diagnosis and treatment is very important. Usually, recovery from ADEM begins within days of treatment and half of those affected will recover completely. Others may have mild to moderate lifelong impairment due to irreparable damage to the nervous system. Severe cases of acute disseminated encephalomyelitis can be fatal, but are much less common. Interestingly, the level of consciousness during the acute phase of the attack most closely correlates with the outcome of the illness, so the less impairment in consciousness, the more likely you will have a full recovery.
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References and Notes
**ADEM after MMR vaccination is a rare occurrence and is usually a more mild course of disease than if it were induced through viral infection. This does not imply that vaccines are unsafe and I do not advocate skipping or delaying vaccinations!
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