Acute disseminated encephalomyelitis (ADEM) and MS

Last updated June 6, 2022, by Marta Figueiredo, PhD
Fact-checked by Ines Martins, PhD

Acute disseminated encephalomyelitis (ADEM) and multiple sclerosis (MS) are both inflammatory autoimmune disorders that damage myelin, the protective fatty sheath around nerve fibers speeding nerve signal transmission.

The conditions share some neurological symptoms. Given their similarities, ADEM — which typically occurs as an isolated event — is sometimes misdiagnosed as a severe first attack of multiple sclerosis. In some cases, however, it can eventually progress to MS.

What is acute disseminated encephalomyelitis?

Known as ADEM, acute disseminated encephalomyelitis is a rare disease characterized by a brief but intense episode of inflammation in the brain and spinal cord that leads to myelin loss, or demyelination. It occasionally also damages myelin in the optic nerve, which relays messages from the eyes to the brain to create visual images.

The disease gets its name from the alterations in consciousness and behavior — “encephalopathy” — that are observed in patients, and the presence of widespread or “disseminated” regions of myelin damage, known as “myelitis.” Neurological symptoms, such as vision problems, weakness, or loss of coordination, also are common in these patients.

Also called post-infectious encephalomyelitis or immune-mediated encephalomyelitis, ADEM is estimated to affect 1 in every 125,000 to 250,000 people in a given year.

Difference between ADEM and MS

Both ADEM and MS cause damage to the myelin sheath, but there are several features that differentiate the two conditions. First, while MS is a disease more commonly affecting women, and developing mainly between the ages of 20 and 50, ADEM is more common in children than in adults, and more often affects men.

ADEM also is typically associated with a recent infection, fever, and change in consciousness, which are not usually observed in people with MS.

In addition, ADEM usually consists of a single episode of widespread inflammation and myelin damage that may last for weeks to months. MS, meanwhile, is characterized by multiple episodes or progressive worsening of symptoms over time.

The two conditions can sometimes be distinguished via MRI scans. If old areas of damaged tissue are detected in the brain and/or spinal cord, the person most likely has MS, as the presence of older lesions suggests repeated demyelinating attacks. ADEM-related lesions also are typically more widespread, with poorly defined margins, compared with those caused by MS.

Differences between the two demyelinating disorders also may be seen in the cerebrospinal fluid, which is the liquid that surrounds the brain and spinal cord. ADEM patients will likely have higher-than-normal levels of white blood cells, suggestive of active or recent infection, but no presence of MS-specific proteins.

Can ADEM turn into MS?

About 20% of patients with ADEM can experience recurring episodes of the disease, happening three or more months after the initial symptoms. Such episodes can have a similar presentation and affect the same regions of the nervous system as the original attack, or they can impact other regions and manifest differently.

It remains unclear if these recurrent episodes of ADEM are actually symptoms of other conditions, such as multiple sclerosis. The current literature estimates that fewer than 10% of ADEM patients eventually meet the diagnosis criteria for MS, but no risk factors have been found, to date, to identify those at higher risk.

Symptoms of ADEM

Most symptoms of ADEM begin within two to 21 days after an infection, and may first present as:

• fever
• headache
• fatigue
• nausea
• vomiting

In addition to these nonspecific manifestations, patients also may develop neurological symptoms. These may include:

• confusion
• excessive irritability
• changes in consciousness that can lead to coma
• loss of vision in one or both eyes
• tingling, numbness, or other unusual sensations
• problems with balance and movement coordination
• muscle weakness that can progress to paralysis
• seizures

The type and severity of ADEM symptoms can vary from one patient to another and are sometimes determined by age of onset. For example, long-lasting fevers and headaches are more common in children, while sensory deficits predominately affect adults.

About 25% to 33% of ADEM patients may have relapses in the future. Research suggests the presence of antibodies against a myelin component called myelin oligodendrocyte glycoprotein (MOG) — located on the sheath’s surface — and seizures at onset are linked to a higher risk of relapse. Most ADEM patients will fully recover, but a few may have lasting mild or moderate impairments.

Risk factors and possible causes of ADEM

ADEM can affect people of any age, but it is more common in young children. In fact, more than 80% of cases occur in children younger than 10.

This autoimmune disease affects people of all ethnicities, and shows a higher frequency with increasing distance from the Equator, similar to the geographic distribution of MS. It also has been reported more commonly in the winter and spring.

The exact cause of ADEM remains unclear. Most scientists believe it is triggered by specific events, such as an infection or vaccination, that result in an abnormal immune system response and in the production of antibodies that wrongly attack myelin. Self-reactive antibodies specifically against MOG are found in 36%–64% of children with ADEM.

While the triggering event of ADEM is never identified in about 20% of patients, some 75% of cases are preceded by an infection or illness. Most of these are upper respiratory tract infections. Also, in about 5% of patients, ADEM has occurred after vaccination, though no direct link has been found to date.

Potential triggers identified to date include:

• viral infections, such as influenza, Epstein-Barr, herpes, and hepatitis, as well as the coronavirus
• bacterial infections, including chlamydia, leptospirosis, and pneumonia
• parasitic infestations, including malaria and toxoplasmosis
• vaccines, especially those against rabies, hepatitis B, polio, influenza, pertussis (or whooping cough), and measles, mumps, and rubella

In addition to these infectious triggers, genetic and environmental factors are believed to contribute to the development of ADEM.

Diagnosis of ADEM

Diagnosing acute disseminated encephalomyelitis generally involves the assessment of a person’s medical history, particularly of recent infections or vaccinations, and physical and neurological examinations. Specific tests that may be used to diagnose ADEM and to rule out other conditions with similar symptoms include:

• MRI, to visualize regions of damage in the brain and spinal cord
• lumbar puncture, also called a spinal tap, to check for signs of active infection or inflammation, and for proteins associated with other diseases
• blood tests, to help assess active infection and rule out other conditions

Treatment of ADEM

While there is no standard treatment for ADEM, people with the condition are usually given high doses of glucocorticoids. These anti-inflammatory and immunosuppressive medications aim to reduce the abnormal inflammatory responses driving nervous system damage.

Such medications also are used to manage acute relapses in people with MS.

If these fail, immunoglobulin therapy and plasmapheresis may be used as secondary treatment options for ADEM.

Immunoglobulin therapy consists of delivering a large number of healthy antibodies directly into the bloodstream. Doing so has the potential to neutralize the abnormal antibodies that are driving immune attacks against myelin.

Plasmapheresis, or plasma exchange, involves removing and replacing a person’s plasma — the liquid portion of blood that contains water, salts, and proteins such as self-reactive antibodies.

ADEM patients also may also receive additional treatments to manage individual symptoms. Long-term management and rehabilitation approaches may be needed to help patients regain some functional abilities and improve their quality of life.

Life expectancy: Is ADEM fatal?

Most people with ADEM will start to recover within days of symptom onset, and show complete or nearly complete recovery within six months. Between 50%–75% of patients fully recover, and these rates rise to 90% when allowing minor residual disability.

It remains unclear if ADEM shortens a person’s life expectancy, but some patients may show mild to moderate lifelong impairments that may impact their quality of life. Potential impairments range from cognitive difficulties to muscle weakness to vision damage to numbness.

In rare, severe cases, particularly those resulting in brain swelling or respiratory difficulties, the disease may also be fatal.

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