Acute disseminated encephalomyelitis

Background

Acute disseminated encephalomyelitis (ADEM) is an immune-mediated inflammatory demyelinating condition that predominately affects the white matter of the brain and spinal cord. The disorder manifests as an acute-onset encephalopathy associated with polyfocal neurologic deficits and is typically self-limiting. ADEM bears a striking clinical and pathological resemblance to other acute demyelinating syndromes (ADS) of childhood, including multiple sclerosis (MS). ADEM in children is readily distinguishable from alternative diagnoses on the basis of clinical features and findings on neuroimaging and laboratory investigations. However, given that ADEM lacks a specific identified biological marker rendering a reliable laboratory diagnosis, long-term follow-up is important as there are instances where an illness initially diagnosed as ADEM is ultimately replaced with a diagnosis of MS.

The onset of ADEM usually occurs in the wake of a clearly identifiable febrile prodromal illness or immunization and in association with prominent constitutional signs and encephalopathy of varied degrees. ADEM is typically a monophasic disease of pre-pubertal children; whereas, MS is typically a chronic relapsing and remitting disease of young adults. Abnormalities of findings on cerebrospinal fluid (CSF) immunoglobulin studies are less common in ADEM. However, the division between these processes is indistinct, suggesting a clinical continuum. Moreover, other conditions along the suggested continuum include optic neuritis, transverse myelitis, and neuromyelitis optica - clinical entities that may occur as manifestations of either MS or ADEM. Other boundaries of ADEM merge indistinctly with a wide variety of inflammatory encephalitic and vasculitic illnesses as well as monosymptomatic, postinfectious illnesses that should remain distinctfromADEM, such as acute cerebellar ataxia (ACA). A further indistinct boundary is shared by ADEM and Guillain-Barré syndrome as manifested in cases of Miller-Fisher syndrome and encephalomyeloradiculoneuropathy (EMRN).

Susceptibility to either ADEM or MS is likely the product of multiple factors, including a complex interrelationship of genetics and exposure to infectious agents and other environmental factors. Of particular interest are the indications that susceptibility to either condition is in part age-related. Most cases of ADEM possibly occur as the result of an inflammatory response provoked by pre-pubertal infection with a virus, vaccine, or other infectious agent. Typically, the manifestations of ADEM occur quickly after this pre-pubertal febrile systemic illness and are monophasic. In a minority of cases, patients with ADEM experience one or two pre-pubertal recurrences followed by remission. MS, on the other hand, typically manifests as a relapsing-remitting illness in ensuing adolescence or young adulthood, a significant and unexplained latency of effect with apparent permanency of immune dysregulation. Bouts of MS occur without a febrile prodrome. Uncommonly, MS develops in pre-pubertal individuals and ADEM develops in post-pubertal individuals. In very rare instances, individuals manifest pre-pubertal ADEM and, after long latency, MS in adolescence.

See more at: https://emedicine.medscape.com/article/1147044-overview