Acute Disseminated Encephalomyelitis (ADEM) is a brief but intense attack of inflammation (swelling) in the brain and spinal cord and occasionally the optic nerves that damages the brain’s myelin (the white coating of nerve fibers). Other terms used to refer to ADEM include post-infectious encephalomyelitis and immune-mediated encephalomyelitis.
ADEM is sometimes difficult to distinguish from multiple sclerosis (MS) because the symptoms common to both "demyelinating" disorders include loss of vision, weakness, numbness and loss of balance. Both ADEM and MS involve immune-mediated responses to myelin in the brain and spinal cord.
What causes ADEM?
The cause of ADEM is not clear but in more than half of the cases, symptoms appear following a viral or bacterial infection, usually a sore throat or cough and very rarely following vaccination. ADEM is thought to be an autoimmune condition where the body’s immune system mistakenly identifies its own healthy cells and tissues as foreign and mounts an attack against them. This attack results in inflammation. Most cases of ADEM begin about 7 to 14 days after an infection or up to three months following a vaccination. In some cases of ADEM, no preceding event is identified.
Who gets ADEM, and when?
Although ADEM can appear at any age, children are more likely than adults to develop it. More than 80 percent of childhood cases occur in patients younger than 10 years. Most of the remaining cases occur between the ages of 10 and 20 but ADEM is sometimes (rarely) diagnosed in adults. ADEM is thought to affect 1 in every 125,000 to 250,000 individuals in a given year. Five percent of these cases could be associated with vaccination.
ADEM appears a little more frequently in boys than girls (about 60 percent of the time) with a male to female ratio of 1.3 : 1.
ADEM appears more often in winter and spring.
ADEM occurs in all parts of the world and in all ethnic groups.
How is ADEM different from MS?
In most but not all cases, ADEM occurs only once, while patients with MS have further, repeated attacks of inflammation in their brains and spinal cords.
In most cases, ADEM patients do not develop new scars on a repeat MRI scan whereas MS patients typically experience new scars on their follow-up MRI scans.
Typical symptoms of ADEM such as fever, headache and confusion, vomiting, and seizures are not usually seen in people with MS, although they can be seen in pediatric MS onset especially in patients younger than 11 years.
Sometimes the pattern of MRI abnormalities helps differentiate these two disorders.
Most patients with MS are treated with ongoing medication to prevent attacks. Patients with ADEM do not require such medication.
ADEM occurs more frequently in males; MS more frequently in females.
ADEM is more common in children; MS is more common in adults.
ADEM occurs more frequently in winter and spring; MS has no seasonal variation.
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