Acute Disseminated Encephalomyelitis (ADEM)

What happens in ADEM

Myelin is the fatty insulation around nerve fibers in the brain and spinal cord that lets signals travel quickly. In ADEM, an immune response, often set off by an infection, mistakenly attacks myelin in many places at once. The result is patches of inflammation and swelling scattered through the white matter of the brain and sometimes the spinal cord and optic nerves.

The leading theory is molecular mimicry: proteins on a virus or bacterium resemble proteins in myelin, so immune cells primed against the infection also attack the nervous system.

ADEM is usually monophasic, meaning it happens once and does not keep coming back, unlike multiple sclerosis.

Causes and triggers

• Viral infections: upper respiratory infections and nonspecific viral illnesses are the most common triggers. Historically, measles was a major cause; varicella (chickenpox), influenza, Epstein-Barr virus and others are also linked.
• Bacterial infections: such as Mycoplasma pneumoniae and streptococcus.
• Vaccines: a very small number of cases follow vaccination. The risk is far lower than the risk of ADEM after the infections those vaccines prevent.
• No identifiable trigger in some people.

ADEM is more common in winter and spring, when infections circulate.

Symptoms

Symptoms typically begin 1 to 3 weeks after an infection and worsen over days, peaking within about 4 days to a few weeks.

Early symptoms

• fever (sometimes returning after the original illness)
• headache
• nausea and vomiting
• tiredness and irritability

Encephalopathy (required for diagnosis)

• drowsiness or difficulty waking
• confusion, behavior changes or irritability
• in severe cases, coma

Neurological signs

• weakness of one or both sides of the body
• unsteady walking and poor coordination (ataxia)
• vision loss from optic neuritis
• double vision or abnormal eye movements
• trouble speaking or swallowing
• numbness or tingling
• seizures
• bladder or bowel problems if the spinal cord is involved (transverse myelitis)

Diagnosis

There is no single test for ADEM. Doctors combine clinical features with tests and exclude other causes such as infection of the brain (encephalitis or meningitis).

• MRI of the brain and spine: the key test. ADEM shows large, fluffy, poorly defined patches in both sides of the white matter, and often in deep gray matter (thalamus and basal ganglia), brainstem and spinal cord. Lesions tend to be of similar age.
• Lumbar puncture (spinal tap): may show mildly raised white cells and protein. Oligoclonal bands, typical of MS, are usually absent.
• Blood tests: including MOG antibodies. Many children with ADEM test positive, which helps predict the course. Aquaporin-4 antibodies are tested to look for neuromyelitis optica.
• Infection tests to identify or exclude active infection.
• EEG if seizures or altered consciousness are present.

ADEM vs multiple sclerosis

A small proportion of children diagnosed with ADEM later develop MS or MOG antibody-associated disease, so follow-up MRI is standard.

Treatment

• High-dose IV corticosteroids (methylprednisolone) for 3 to 5 days, followed by a tapering course of oral steroids over several weeks. This is first-line treatment and speeds recovery.
• IV immunoglobulin (IVIG) if steroids are not effective or cannot be used.
• Plasma exchange for severe cases not responding to other treatments.
• Supportive care: intensive care for breathing support or decreased consciousness, anti-seizure medicines, and treatment of brain swelling.
• Rehabilitation: physical, occupational and speech therapy.

Complications and outlook

Most children make a full or near-full recovery over weeks to months. Some have lasting problems, including:

• difficulties with attention, memory, processing speed or behavior
• weakness or coordination problems
• vision problems
• epilepsy

Adults tend to have a more severe course. Death is uncommon but can occur in severe cases, particularly in the rare hemorrhagic form (acute hemorrhagic leukoencephalitis).

Relapses: a second ADEM-like episode is called multiphasic ADEM. Recurrent episodes, especially with MOG antibodies, may point to a chronic condition needing longer-term treatment.

Frequently asked questions

What causes ADEM?

ADEM is usually triggered by an infection, most often a viral respiratory illness. The immune system responds to the infection but then mistakenly attacks myelin in the brain and spinal cord. Rarely, it follows vaccination. Sometimes no trigger is found.

What are the symptoms of ADEM?

ADEM typically starts with fever, headache and vomiting, then drowsiness or confusion, followed by neurological symptoms such as weakness, unsteady walking, vision loss, double vision, speech problems, numbness or seizures. Symptoms develop over days and need emergency assessment.

Is ADEM the same as multiple sclerosis?

No. ADEM is usually a single episode, affects young children, and follows an infection with fever and drowsiness. MS is a lifelong condition with repeated relapses, usually in young adults. A small number of children with ADEM later develop MS, so follow-up is needed.

Can you fully recover from ADEM?

Yes, many people do. Most children recover fully or almost fully within weeks to months after treatment. Some have lasting difficulties with thinking, behavior, vision or movement. Adults tend to have a more severe course.

Is ADEM contagious?

No. ADEM itself is not contagious, because it is an immune reaction rather than an infection. The infection that triggered it may be contagious, but most people with that infection do not develop ADEM.