Acute disseminated encephalomyelitis (ADEM) is a rare disease estimated to affect about 1 in 125,000-250,000 people every year. Of these diagnosed cases, about 50-60% are due to a prior infection and 40-50% are likely autoimmune in origin. Less than 5% of cases due to infection may have been caused by an inflammatory response to a vaccine. 

Children are more likely to be diagnosed with ADEM than adults, with 80% of cases diagnosed in children under 10 years and the remaining 20% of cases diagnosed between the ages of 10-20 years. It is also more common in children assigned male at birth, about 60% of cases compared to 40% of diagnosed cases in children assigned female at birth. ADEM is commonly diagnosed in the winter and spring, which could be due to higher cases of infection during this time period.

Acute disseminated encephalomyelitis (ADEM) is caused by swelling and inflammation in regions of the brain that damages myelin surrounding nerve cell axons. This swelling and inflammatory response can be due to an infection or an autoimmune response. About half of all diagnosed cases are associated with an infection, which can cause symptoms to develop within 4-14 days, and the other half of diagnosed cases are classified as autoimmune. Post-infection cases are caused by bacterial or viral infections that occur in children and cause their antibodies to wreak havoc on their immune system. In very rare cases, a vaccination may cause this inflammatory response and ADEM to occur. Autoimmune cases are likely caused by a particular type of auto-antibody directed against myelin oligodendrocyte glycoprotein (MOG). These auto-antibodies target the myelin sheath around nerve cells and break it down, and they have been detected in about 36-64% of children who were diagnosed with ADEM.

The symptoms of acute disseminated encephalomyelitis (ADEM) are indicative of both an infection and subsequent nerve damage. Early signs of ADEM indicate that an inflammatory response has occurred:

• Fever and sickness

• Headache

• Nausea and vomiting

• Seizures

After inflammation has caused damage to the myelin in the brain (demyelination), certain signaling pathways are affected. These can affect motor functions and other bodily functions, causing the following symptoms:

• Muscle weakness, especially in the arms and legs

• Numbness or tingling sensation

• Loss of vision

Acute disseminated encephalomyelitis (ADEM) is a rare disease with similar symptoms to other demyelinating disorders (those that damage myelin in the brain). This includes multiple sclerosis, a chronic disease causing damage to myelin to take place over time and cause increasing damage to bodily functions. To distinguish between ADEM and MS, there are a few characteristics of each disease that help with an initial diagnostic pathway:

Additional testing can aid in distinguishing a diagnosis of acute disseminated encephalomyelitis (ADEM) from other demyelinating disorders such as MS. These mainly focus on determining that damage to the myelin occurred as a single instance and was the result of antibodies and inflammation in the brain:

1. Magnetic resonance imaging (MRI) - Imaging areas of the brain detects lesions to myelin caused by inflammation. It is important to follow up with multiple MRIs to make sure that no further damage occurs, which indicates a diagnosis of ADEM over more chronic MS.

2. Auto-antibody testing in cerebrospinal fluid (CSF) - A lumbar puncture and extraction of cerebrospinal fluid (CSF) allows for the analysis of immune cells present that could potentially be causing inflammation of the brain. The presence of myelin oligodendrocyte glycoprotein (MOG) auto-antibodies is especially indicative of an ADEM diagnosis.

Acute disseminated encephalomyelitis (ADEM) is a rare disease with no known cure, and treatments focus on reducing inflammation and preventing future incidences of myelin damage. To this end, the following have been shown to improve symptoms of ADEM:

1. Corticosteroids - Drugs such as methyl-prednisolone (Solu-Medrol) aim at immune-suppression and reducing inflammation. 

2. Plasma exchange (plasmapheresis) - The removal of one’s immune cells that may be causing an autoimmune response can improve symptoms of ADEM. This is accomplished by circulating blood from the body through a machine that separates out components from the immune system and then returns the blood to circulation.

3. Immunoglobulin therapy - Immunoglobulin is an antibody that specifically targets immune cells and destroys them. Injections of immunoglobulin can help reduce auto-antibodies in the blood and prevent further inflammation.

Acute disseminated encephalomyelitis often presents as a one-time occurrence of inflammation in the central nervous system. If the damage to myelin sheaths surrounding nerve cells is not extensive, and if the inflammation can be prevented from happening again, children with ADEM often recover and lead healthy lives. For most children diagnosed with ADEM who receive treatment, they begin to recover within days. Some will have lasting effects of nerve damage such as blurred vision, weakness or numbness, or lower muscle movement.

1. https://www.ninds.nih.gov/health-information/disorders/acute-disseminated-encephalomyelitis#:~:text=Acute%20disseminated%20encephalomyelitis%20(ADEM)%20is,helps%20with%20electrical%20nerve%20signaling.

2. https://www.nationalmssociety.org/What-is-MS/Related-Conditions/Acute-Disseminated-Encephalomyelitis-(ADEM)

3. https://rarediseases.org/rare-diseases/acute-disseminated-encephalomyelitis/

4. https://n.neurology.org/content/87/9_Supplement_2/S38

5. https://my.clevelandclinic.org/health/diseases/14266-acute-disseminated-encephalomyelitis-adem

6. https://www.childrenshospital.org/conditions/acute-disseminated-encephalomyelitis-adem

7. https://emedicine.medscape.com/article/1147044-overview