Acute Disseminated Encephalomyelitis

Acute Disseminated Encephalomyelitis

Acute disseminated encephalomyelitis is an acute illness characterized by inflammation and demyelination in the brain, spinal cord and may involve the optic nerves.

Symptoms of ADEM

There are numerous rapidly evolving neurological symptoms that reflect an extensive involvement of the whole central nervous system in the disease process.
They are weakness, loss of vision, lack of balance, incontinence, loss of speech and memory, fever, headaches, nausea, vomiting, irritability, confusion, drowsiness, which may progress to coma. Seizures are common.
The symptoms are rapidly progressing over hours to days likely leading to death without treatment.

Cause of ADEM

ADEM is a monophasic autoimmune disease which does not tend to recur. The autoimmune attack is launched against some normal myelin component (e.g. myelin basic protein). The onset of acute disseminated encephalomyelitis often follows immunization or some infection (2 days to 4 weeks prior). In the past, it was often associated with smallpox, Semple rabies, and older versions of measles vaccine.
ADEM is much more common in children. Most children affected are between 5 and 8 years old. The infections associated are measles, chickenpox, flu, mononucleosis, rubella, mumps, and Mycoplasma Pneumonia.

Infections and vaccinations do not cause ADEM. They only trigger this disease. The likely mechanism is so called molecular mimicry.
Some of the trigger-agent components look alike with normal myelin from the immune system prospective. An immune attack launched against the invading microbe damages myelin because of structural similarity of their components.
There is a wide-spread damage to the central nervous system. Multiple lesions are formed throughout the brain, spinal cord, and sometimes optic nerves. Unlike MS, the lesions are not limited to the white matter. Deep gray matter may be involved as well.

Diagnosis of ADEM

There are no strict diagnostic criteria for the acute disseminated encephalomyelitis. Brain MRI shows multiple similar to MS lesions throughout the brain. Both sides of the brain are usually equally involved.
Unlike MS, involvement of deep brain gray matter is not unusual (basal ganglia and thalamus). Spinal cord MRI typically demonstrates contrast enhancing lesions.
Cerebrospinal fluid characteristic findings are elevated protein and moderate elevation of cell count (mononuclear). IgG index and oligoclonal bands are negative.

There are multiple conditions that might have similar symptoms: neurosarcoidosis, vasculitis due to other autoimmune disease, progressive multifocal leukoencephalopathy (PML, infection caused by JC virus), CNS Lymphoma, posterior reversible encephalopathy syndrome due to severe hypertension or chemotherapeutic drugs, or paraneoplastic syndromes.

Marburg form of MS can have similar picture at the onset, but its course is much more malignant. It frequently leads to death within days or weeks in spite of treatment.

Treatment of Acute Disseminated Encephalomyelitis

The most widely accepted treatment is a high dose IV steroids followed by oral steroids for a few weeks.
Lack of response to steroids necessitates a trial of IV Immune Globulin or Plasma Exchange. These treatment modalities are also effective, but they are much more expensive.

Prognosis of ADEM

Prognosis is variable and no statistics is available. In general, ADEM prognosis is rather favorable with the right treatment. Presence of severe seizures (status epilepticus) carries worse prognosis.

Acute disseminated encephalomyelitis is usually an acute monophasic illness. The symptoms might fluctuate for up to 3 months but eventually subside. The level of residual disability is variable.

Recurrent form of ADEM is an exception rather than the rule. ADEM is called recurrent if the symptoms come back 3 month or more after the first attack, providing the treatment was stopped at least a month prior.
Follow up MRIs do not show any new lesions but the original lesions may enlarge. Basically, it is a protracted course of the same attack.

Another form of prolonged disease course is called Multiphasic ADEM. New symptoms start within the same time frame as in recurrent ADEM.
Follow up MRI shows new lesions while the old lesions are in the process of resolution.