Acute disseminated encephalomyelitis
Acute disseminated encephalomyelitis, also known as ADEM, is a neurological disorder that causes brief but intense inflammation of the spinal cord and brain. ADEM usually follows a viral infection. In rare cases, it has been linked to the mumps, measles, and rubella vaccine.
Definition & Facts
Acute disseminated encephalomyelitis can affect anyone, but it is most often seen in children. It appears that ADEM affects males and females in relatively equal numbers. Some studies indicate a slight increase in the number of ADEM cases in the winter and spring.
Approximately half of ADEM patients report having an illness shortly before developing the condition. In most instances, the illness was a simple upper respiratory tract infection. The long-term prognosis for patients with ADEM is generally good with most patients achieving a full recovery.
In rare cases, ADEM can cause permanent damage to the myelin that insulates and protects the nerves, which can lead to life-long neurological impairment. A very small percentage of individuals with acute disseminated encephalomyelitis may go on to develop multiple sclerosis.
Symptoms & Complaints
The severity and progression of ADEM symptoms can vary from person to person. Symptoms may also be affected by the patient’s age at the time of onset. For example, fevers and headaches are more common in children while sensory deficits tend to occur primarily in adults.
ADEM is sometimes mistaken as a first attack of multiple sclerosis since the symptoms are very similar. A key difference is that ADEM usually consists of one attack that resolves over a period of weeks or months while multiple sclerosis typically features multiple episodes. Another differentiating factor is that multiple sclerosis does not usually cause fever or coma.
Acute disseminated encephalomyelitis is believed to be triggered by an immune system reaction to an infection. Instead of attacking the source of the infection, the immune system attacks the central nervous system, which causes inflammation. Inflammation is the body’s way of responding to and attempting to remove harmful stimuli, including damaged cells, irritants, and infectious agents.
Most cases of ADEM occur within one to two weeks following a viral or bacterial infection or within three months following a vaccine. In rare cases, no precipitating event can be identified. It should be noted that the risk of developing ADEM following a vaccine is very rare, and parents should not forego routine vaccines recommended by their child’s doctor.
The most common infections associated with ADEM include upper respiratory infections, influenza, mumps, measles, rubella, Epstein-Barr virus, and cytomegalovirus (CMV) infection. Genetic factors and environmental factors may also play a role in the development of ADEM; however, more research is needed to identify the exact causes and mechanisms.
Diagnosis & Tests
Acute disseminated encephalomyelitis should be considered anytime there is a close connection between a bacterial or viral infection and a sudden onset of one or more neurological symptoms. A magnetic resonance imaging (MRI) scan of the brain will typically reveal diffuse changes deep in the white matter of the brain, which contains the nerve fibers of the brain and spinal cord. These changes may affect more than half of the brain’s total white matter. There may also be visible lesions in the gray matter of the brain.
A lumbar puncture to remove a sample of cerebrospinal fluid is often used to rule out infections and processes that may appear similar to ADEM. Cerebrospinal fluid is a clear, colorless fluid that cushions the brain and circulates in and around the brain and spinal cord. In cases of ADEM, the spinal fluid often shows an increase in white blood cells called lymphocytes, which are part of the body’s immune system. The fluid can also be cultured to try to identify the specific organism that triggered the ADEM.
Treatment & Therapy
ADEM is rare and has not been extensively studied in clinical trials. Controlled, randomized trials involving adults and children are needed to evaluate the various therapies in order to determine the optimal treatment protocol.
Currently, treatment is directed at reducing the brain and spinal cord inflammation. This usually involves intravenous methylprednisolone or other corticosteroid medications. The IV steroids are usually given for five to seven days and followed by a gradually decreasing dose of oral steroids. Short-term steroid therapy does come with a number of side effects including:
- Mood swings
- Increased blood sugar
- Low potassium
- Weight gain
- Facial flushing and facial swelling
Intravenous immune globulin (IVIG) may be used in patients that do not respond to steroid therapy. IVIG therapy involves infusions of a blood product that has been shown to reduce the activity of certain autoimmune diseases. The infusions are usually given over several hours over the course of five days.
Another approach to treating ADEM involves plasmapheresis. This treatment usually requires that the patient be hospitalized. A central venous catheter is inserted so that blood can be withdrawn quickly. The blood is then circulated through a machine to remove any immune system components before it is introduced back into the body. The process usually takes several hours every day over a period of 10 to 14 days. In rare cases, patients undergoing plasmapheresis may experience an allergic reaction to the blood product or bleeding because of the reduced number of platelets.
Prevention & Prophylaxis