What is acute disseminated encephalomyelitis?
Acute disseminated encephalomyelitis (ADEM) is a rare neurological disorder. It affects children more than adults, but can affect anyone.
What are the causes and/or risk factors associated with acute disseminated encephalomyelitis?
We know that ADEM usually follows an infection of some kind. In 50% to 75% of cases, the beginning of the disease is preceded by a viral or bacterial infection, usually a sore throat or cough (upper respiratory tract infection). Many different bacteria, viruses and other infections have been related to ADEM, but the disease does not appear to be caused by any one infectious agent. Most cases of ADEM begin about 7 to 14 days after the infection.
On occasion, ADEM occurs after a vaccination. This is rare overall, but when it happens, it usually occurs after the measles, mumps, and rubella vaccination. In these cases, ADEM may occur up to 3 months after the vaccination.
ADEM appears to be an immune reaction to the infection. In this reaction, the immune system, instead of fighting off the infection, causes inflammation in the central nervous system. Inflammation is defined as the body's complex biological response to harmful stimuli, such as infectious agents, damaged cells, or irritants. Inflammation is a protective attempt to remove the injurious stimuli and initiate the healing process. In the case of ADEM, the immune response is also responsible for demyelination, a process in which the myelin that covers many nerve fibers is stripped off.
What are the symptoms of acute disseminated encephalomyelitis?
More than half of patients have an illness, usually an infection, 2 to 4 weeks before developing ADEM. Most of these illnesses are viral or bacterial, often no more than an upper respiratory tract infection. In children with ADEM, prolonged and severe headaches occur. In addition, the patient develops fevers during the ADEM course.
Along with this pattern, the patients usually get neurological symptoms which may include:
- Confusion, drowsiness, and even coma
- Unsteadiness and falling
- Visual blurring or double vision (occasionally)
- Trouble swallowing
- Weakness of the arms or legs
In adults with ADEM, motor (movement) and sensory (tingling, numbness) symptoms tend to be more common. Overall, what triggers a diagnosis of ADEM is a rapidly developing illness with neurological symptoms, often with fever and headache, usually following an upper respiratory tract infection, and which has significant MRI and spinal fluid findings consistent with ADEM.