What causes acute disseminating encephalomyelitis?

The exact cause of acute disseminated encephalomyelitis (ADEM) is unknown, but it is thought to be an autoimmune response that occurs after a viral or bacterial infection, with the body's immune system attacking its own brain and spinal cord tissues.

Common triggers of ADEM include viral infections such as measles, mumps, rubella, chickenpox, Epstein-Barr virus, influenza, COVID-19, as well as Mycoplasma pneumoniae and other bacterial infections. Following certain vaccinations has also been implicated as another triggering mechanism, although this risk is extremely rare.