Acute Disseminated Encephalomyelitis (ADEM)

Acute disseminated encephalomyelitis (ADEM) is an inflammation of the brain and spinal cord. ADEM is a demyelinating disease of the brain and spinal cord. Demyelination is the destruction or loss of the myelin from the sheath. The inflammation is caused by an autoimmune attack, a hypersensitivity reaction of the brain. Often the attack is a response to a viral infection. Sometimes ADEM occurs after immunization or it may be a manifestation of other diseases such as multiple sclerosis. It is not a common disease. Most of the preceding infections are typically upper respiratory tract infections. It can occur at any age, but is most common in children.

Etiology (Causes)

Some of the more common causes following infection have been measles, chicken pox, rubella and influenza. Occasionally a bacterial infection causes ADEM.

Following immunization, vaccination such as the smallpox vaccine and rabies vaccine, may cause ADEM.

The development of ADEM usually occurs over several days or a week or two. And, again, the disease is most common in childhood.

Symptoms and Signs

There are various neurological symptoms and signs that include headache and fever and altered mental status. A respiratory illness or a gastrointestinal disease may precede these various neurologic symptoms and signs. The level of consciousness may be impaired and the patient may be confused and even become comatose. Seizures sometimes occur. Also, there may be meningeal irritation and weakness including of the extremities. Also, there may be loss of sensation. Ataxia with unsteadiness also occurs. The optic nerve and other cranial nerves are sometimes involved and when the intracranial pressure becomes involved, accompanying symptoms also appear, such as headache and vomiting.

Diagnosis and Investigation MRI

MRI can be very helpful and quite sensitive. CT scans may be used, but MRI is a superior study as compared to CT for ADEM. The MRI can detect the lesions that can be widespread in the brain, such as the white matter with the lesions occurring primarily in the cerebrum as well as other areas within the brain and spinal cord. Occasionally the lesions do not resolve entirely. However, usually there are no new lesions after six months.

CT is not as sensitive as MRI. However, it still can be helpful because it is usually quite available and may rule out other disease processes.

CSF

CSF testing refers to testing of the spinal fluid. The CSF often shows lymphocytes. The testing may also indicate that the protein is elevated but the blood glucose is normal. CSF may be tested for different viruses, and viral cultures may also be done.

Brain Biopsy

If a patient is not doing well, a biopsy of the brain may be performed.

Various other studies may also be performed, including laboratory work that could consist of chemistries and blood counts. Chest x-ray and urinanalysis and an electroencephalogram (EEG) could also be investigated.

Treatments

Antibiotics may be used if there is a consideration of a bacterial infection and acyclovir can be used when considering herpes simplex virus causing an encephalitis.

Steroids are often used such as intravenous methylprednisolone. If methylprednisolone is not sufficient treatment, then intravenous immunoglobulins may be attempted. Therapy could also include plasma exchange.

Additionally, supportive care is utilized including medication for fever and treatment with fluids and, if necessary, medication for seizures.

Prognosis

Complications and mortality varies. The most frequent sequelae follow measles. The most serious neurological defects occur in infants.

References

• Clinical Neurology, 9^th Edition, 2015
• Hankey’s Clinical Neurology, 2^nd Edition, 2014
• The Merck Manual, 19^th Edition, 2011

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