Chapter 556

The central role of the immune system in several pediatric central nervous system (CNS) disorders has been increasingly appreciated in recent years. Although relatively rare as individual diseases, collectively they constitute a sizable proportion of pediatric neurology practice. The acute, severe symptoms associated with these disorders usually lead to inpatient hospitalization. Due to the broad differential diagnoses associated with these conditions, multiple other pediatric subspecialists, such as infectious disease and rheumatology physicians, are often asked to evaluate affected patients. Last, because of the potential long-term sequelae of both the monophasic and recurrent immune-mediated CNS disorders, all aspects of a patient’s medical and psychosocial care can be affected. Thus, these disorders have relevance to general pediatricians and pediatric subspecialists in both the inpatient and outpatient settings.

Demyelinating disorders comprise the largest subgroup within CNS immune-mediated disorders. Myelin is composed of a lipid bilayer of cholesterol, phospholipids, and glycolipids along with membrane-associated proteins, such as proteolipid protein and myelin basic protein.1,2 In the CNS, oligodendrocytes produce myelin, which surrounds axons with periodic interruptions at nodes of Ranvier. The main functions of myelin are to speed the conduction of action potentials along axons and to support the development and maintenance of axons.

Myelin can be injured by many different mechanisms, such as hypoxia, metabolic derangements, and toxic insults. The disorders discussed in this chapter are considered to have an autoimmune etiology, with loss of tolerance resulting in an aberrant, self-reactive inflammatory process directed against CNS myelin.

Demyelination leads to slowing or blockade of action potential propagation, with resulting symptoms referable to the affected CNS areas. Although remyelination can occur in the CNS, the thickness of the original myelin sheath is never reachieved.3 Demyelination can also lead to secondary axonal loss, which leads to permanent disability.4

### First Attack of Demyelination

#### Definitions, Terminology, and Classification

In the past, variable terminology and lack of consistent definitions in the literature hampered our understanding of pediatric CNS demyelinating disorders. In April 2007, diagnostic definitions were proposed by the International Pediatric Multiple Sclerosis (MS) Study Group.5 Although they have not yet been prospectively validated, these definitions provide a very useful framework both for clinical and research purposes.

With a first presentation of a CNS demyelinating disorder, determining whether mental status changes are present or absent serves as the initial step in classification (Fig. 556-1). When present and accompanied by multifocal symptoms, the appropriate diagnosis is acute disseminated encephalomyelitis (ADEM), which can be confirmed with magnetic resonance imaging (MRI). When the patient’s mental status is normal, first-time acute demyelinating events are collectively referred to as clinically isolated syndromes (CIS). Clinically isolated syndromes can be subdivided based on whether the symptoms and signs are focal or multifocal. Common locations for focal CIS include the optic nerve (optic neuritis), spinal cord (transverse myelitis), brain stem, and cerebellum. If ...

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