ADEM (Acute Disseminated Encephalomyelitis)

What happens in ADEM

In ADEM, the immune system, primed by an infection, mistakenly attacks myelin in the central nervous system. This is thought to happen through molecular mimicry, where proteins from a germ resemble proteins in myelin. Inflammation develops in many places at once ("disseminated") in the white matter of the brain, the brainstem, the optic nerves and the spinal cord.

Unlike multiple sclerosis, ADEM is usually a one-time (monophasic) illness.

Causes and triggers

• Viral infections are the most common trigger: upper respiratory infections, measles, chickenpox, mumps, rubella, influenza, Epstein-Barr virus and others.
• Bacterial infections such as Mycoplasma pneumoniae and streptococcus.
• Vaccinations, very rarely. The risk after modern vaccines is far lower than the risk after the infections they prevent; ADEM was more common after measles before vaccination.
• In many cases, no trigger is identified.

It occurs in roughly 0.2 to 0.8 per 100,000 children a year, more often in winter and spring.

Symptoms

Symptoms develop over hours to days, often after a few days of fever and headache.

Encephalopathy (required for diagnosis)

• Drowsiness or lethargy, progressing in severe cases to coma
• Confusion, irritability or behavior changes

Neurological deficits

• Weakness of one side or both legs
• Unsteady walking and poor coordination (ataxia)
• Vision loss from optic neuritis, often in both eyes
• Double vision, difficulty speaking or swallowing
• Numbness or tingling
• Bladder problems from spinal cord involvement (transverse myelitis)
• Seizures

General symptoms

• Fever, headache, vomiting and neck stiffness

ADEM vs multiple sclerosis

Diagnosis

There is no single test; ADEM is diagnosed by combining features and excluding other causes, especially infection of the brain.

• MRI of the brain and spine: large, patchy, poorly defined lesions in white and deep gray matter.
• Lumbar puncture: spinal fluid may show raised white cells and protein; testing excludes encephalitis and meningitis.
• Blood tests: including MOG antibodies, found in about half of children with ADEM, and AQP4 antibodies to exclude neuromyelitis optica.
• Infection tests to look for the trigger.
• EEG if seizures or reduced consciousness.

Treatment

• High-dose IV methylprednisolone for 3 to 5 days, usually followed by a tapering course of oral steroids over several weeks.
• IV immunoglobulin (IVIG) if steroids are not enough or cannot be used.
• Plasma exchange for severe cases not responding to other treatments.
• Supportive care: intensive care for reduced consciousness or breathing problems, seizure treatment, nutrition and bladder care.
• Rehabilitation: physical, occupational and speech therapy.

Outlook

Most children make a full or near-full recovery, with improvement starting within days and continuing over weeks to months. Some have lasting difficulties with attention, memory, behavior, vision or coordination. Severe cases can be fatal, but this is uncommon with modern care.

ADEM recurs in a minority, particularly those with MOG antibodies. Further attacks may be diagnosed as MOG antibody-associated disease (MOGAD), MS or neuromyelitis optica, so follow-up with repeat MRI is important.

Frequently asked questions

What causes ADEM?

ADEM is caused by the immune system attacking myelin in the brain and spinal cord, usually triggered by a recent infection such as a cold, flu, chickenpox or measles. Rarely it follows a vaccine. In many cases, no specific trigger is found.

Is ADEM the same as multiple sclerosis?

No. ADEM is usually a one-time illness, mostly in young children, with drowsiness or confusion and often fever. MS is a lifelong condition with repeated relapses, typically in young adults. A small number of people first diagnosed with ADEM are later found to have MS.

Can you fully recover from ADEM?

Most children recover fully or nearly fully, usually over weeks to a few months. Some have ongoing problems with concentration, behavior, learning, vision or balance. Adults may recover more slowly. Rehabilitation helps maximize recovery.

Can ADEM come back?

ADEM usually happens only once. A minority of people have a second episode, especially those with MOG antibodies. Repeated attacks may lead to a diagnosis of MOG antibody-associated disease, multiple sclerosis or neuromyelitis optica, which are treated differently.