ADEM: distinct disease or part of the MS spectrum?

Abstract

Acute disseminated encephalomyelitis (ADEM) is a rare inflammatory demyelinating disease of the CNS affecting predominantly children and young adults. Typically, it is antedated by an infectious illness, most commonly measles, mumps, influenza A or B, Rocky Mountain spotted fever, or hepatitis A or B, or infection with herpes simplex, human herpesvirus 6, varicella, rubella, vaccinia, Epstein–Barr virus, cytomegalovirus, Mycoplasma pneumoniae, Chlamydia, Legionella, Campylobacter, or Streptococci . ADEM can also follow immunizations: rabies, diphtheria–tetanus–pertussis, smallpox, measles, Japanese B encephalitis, and hog.1,2⇓ Characteristic clinical features include sudden onset of multifocal neurologic disturbances such as bilateral optic neuritis, visual field defects, aphasia, motor and sensory deficits, ataxia, movement disorders, and signs of an acute meningoencephalopathy with meningismus, a depressed level of consciousness, focal or generalized seizures, and psychosis. Maximal deficits are reached within several days and remission may be similarly rapid. More often, however, resolution is partial and takes weeks or months. High mortality rates (up to 20%) were frequent in the past, particularly when ADEM followed measles. However, with the introduction of effective vaccination strategies and the decline of measles, death is rare.2 MRI reveals multifocal areas of increased signal intensity on T2-weighted sequences that commonly enhance synchronously with contrast medium.3,4⇓ Extensive perifocal edema may be seen. White matter involvement predominates but gray matter can also be affected, particularly basal ganglia, thalami, and brainstem. Lesions may also be restricted to the brainstem or cerebellum. Tumor-like lesions also occur. CSF usually shows pleocytosis but only rarely intrathecal oligoclonal immunoglobulin (Ig) G production, which almost invariably ceases as patients improve. Whereas high-dose steroids, plasma exchange, IVIg, immunomodulators, and hypothermia have been tried, no treatment is established.5-9⇓⇓⇓⇓ This textbook view of ADEM is based on a compilation of features extracted from single cases and small …