Overview:
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.
ADEM Diagnoses:
The diagnosis of ADEM needs to be considered whenever there is a close relationship between an infection and the development of more than one neurological symptom, which are often accompanied by headache, fever, and an altered mental state. The symptoms tend to worsen over a few days, making it clear that the problem is a serious one.
MRI Scanning:
Magnetic resonance imaging (MRI) scanning is an important part of the diagnosis. In ADEM, there are usually widespread, multiple changes deep in the brain in areas known as the white matter. The white matter is the part of the brain and spinal cord that contains the nerve fibers.
These nerve fibers are often covered by the protective coating called myelin, which looks white compared with the grey matter, which contains the nerve cells. There are also sometimes lesions in the grey matter deep in the brain as well. Often the areas affected can be more than half of the total volume of the white matter.
While these changes are characteristic, they are not specific for ADEM. The health care professionals in these cases must consider other diagnoses, such as multiple sclerosis (MS), direct brain infections, and sometimes tumors.
Over months these changes on MRI should gradually improve and even completely disappear.
Spinal Fluid Testing:
A lumbar puncture is typically needed in patients with ADEM. This is partially to rule out direct infections or other processes that can look like ADEM. The lumbar puncture allows the neurological team to test the cerebrospinal fluid for many different things that assist in the diagnostic process.
The cerebrospinal fluid (CSF) or spinal fluid is a clear, colorless fluid that circulates in around the brain and spinal cord. It cushions the brain from hitting the inside of the skull, and may be important in removing chemicals from the brain.
In ADEM, the spinal fluid often shows an increase in white cells, usually lymphocytes. These cells are an active part of the immune system. Occasionally doctors can culture or measure a reaction to a specific virus or bacteria in the spinal fluid that may have triggered ADEM. In ADEM, there are often no oligoclonal bands. Oligoclonal bands are abnormal bands of proteins seen in certain spinal fluid tests that indicate activity of the immune system in and around the spinal fluid pathways. These bands are commonly found in multiple sclerosis. This difference may help to distinguish ADEM from MS.
ADEM Treatment:
ADEM is a rare disease, and so there are no well-designed clinical trials comparing one treatment with placebo, or one treatment with another. Everything we know about treatment in ADEM comes from small published series of cases, and there are no guidelines for treatment of ADEM yet.
At this time, intravenous methyl-prednisolone (for instance, Solu-Medrol®) or other steroid medications are the front-line treatment for ADEM. Usually these medications are given over a five- to seven-day course, followed by a tapering dose of oral steroids. The aim is to reduce inflammation and speed recovery from the disease.
Patients on steroids need to be monitored for increased blood glucose, low potassium, and sleep disturbance. There may be mood changes (irritability, crying, anxiety) when people are on steroid therapy. Other short-term complications of steroid therapy include weight gain, flushed cheeks, facial swelling, and a metallic taste (when using IV Solu-Medrol).
If a patient does not respond to IV methylprednisolone, the next line of treatment may be intravenous immune globulin (IVIG). This is an intravenous treatment using a blood product which has been shown to reduce the activity in certain immune diseases, including ADEM. Treatment is usually given for a few hours daily over five days for ADEM. IVIG has the same risks as any blood product (allergic reaction, infection); it also sometimes causes shortness of breath due to fluid overload. Rarely, patients lack an antibody important to the system and may react more strongly to IVIG.
Another approach to treatment is a process called plasmapheresis. This is a treatment in which the blood is circulated through a machine that withdraws components of the immune system from the circulation, reducing immune activity. It is usually a process which takes a few hours and is done every other day for 10 to 14 days, often as part of a hospital stay. It may require the placement of a central venous catheter to allow for blood to be removed from the system rapidly. Risks of plasmapheresis include discomfort from taking blood, sometimes a tendency to bleed due to a reduction in platelets, and infections.
In very severe cases, chemotherapy may be necessary. Either cyclophosphamide or mitoxantrone can be used, but only if less toxic therapies are not effective.
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