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Demyelination is a process that results in either partial or complete loss of the myelin sheath following a period of normal myelin development. Demyelinating diseases may affect the central nervous system (CNS), the peripheral nervous systems (PNS), or both. CNS demyelination may occur as a result of direct damage to the myelin sheath and/or the oligodendrocytes (primary demyelination), or is secondary to axonal damage with subsequent disruption of the axon-glia interaction essential to maintain normal myelination (secondary demyelination). Acquired CNS demyelinating diseases include self-limited monophasic disorders, such as acute disseminated encephalomyelitis (ADEM), as well as chronic, recurrent conditions such as multiple sclerosis (MS) and neuromyelitis optica (NMO). On the other hand, dysmyelination is a genetic or developmental abnormality of the myelin sheath seen in various leukodystrophies such as adrenal leukodystrophy and metachromatic leukodystrophy. A discussion of dysmyelinating diseases is beyond the scope of this chapter, which focuses on childhood demyelinating diseases of the CNS. In the last few years there has been increased interest in studying childhood-onset MS, and our understanding of acquired demyelinating disorders is increasing exponentially.
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Multiple sclerosis (MS) is an acquired, immune-mediated, demyelinating disease affecting the brain and the spinal cord. Despite reports of childhood-onset MS1-3 soon after the initial descriptions of MS by Jean Marie Charcot,4 the diagnosis of MS in childhood was disputed for a long time. In addition, early on, the misdiagnosis of a number of diseases as MS, including leukodystrophies, metabolic disorders, and tumors, and the confusion surrounding the use of various terms to describe a single disorder, cast further doubt on the existence of childhood-onset MS.5 Although a few reports of childhood-onset MS6,7 were still published in the literature, on the whole, childhood-onset MS was largely ignored by both the researchers and the clinicians. In fact, one of the early diagnostic criteria8 proposed for the diagnosis of MS specifically restricted this diagnosis to patients between the ages of 10 and 50 years. The recognition of the fact that MS occurs as a distinct disease in children was brought forth by a series of articles published in the late 1950s and early 1960s.9-11 Later publications firmly established the occurrence of MS in children under the age of 18 years, even as early as infancy.12-15 Despite this renewed interest, the epidemiology, genetics, and natural history of pediatric-onset MS remain unclear at the present time.
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With an increasing number of reports being published, the clinical features of childhood-onset MS are beginning to be understood better. Despite limited natural history data, a clearer picture of this disease in children is emerging. The mean age of onset in most studies is reported to be between 8 and 14 years. Infants as young as 10 months have been reported to have findings suggestive of MS.15 In this case, which probably represents the earliest onset of MS in published literature, a girl developed five ...