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, numerous 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.
CNS IMMUNE-MEDIATED DEMYELINATING DISORDERS
Demyelinating disorders comprise the largest subgroup within CNS immune-mediated disorders. 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. Demyelination can also lead to secondary axonal loss, which leads to permanent disability.
THE FIRST EPISODE OF DEMYELINATION
DEFINITIONS, TERMINOLOGY, AND CLASSIFICATION
With a first presentation of a CNS demyelinating disorder, determining whether the symptoms and signs are focal or multifocal serves as the initial step in classification (Fig. 548-1). Common locations for focal presentations include the optic nerve (optic neuritis), spinal cord (transverse myelitis), brain stem, and cerebellum, which collectively are termed clinically isolated syndromes (CIS). When multifocal symptoms and signs are present and accompanied by encephalopathy, the appropriate diagnosis is acute disseminated encephalomyelitis (ADEM), which can be further supported with magnetic resonance imaging (MRI). If multiple CNS locations are involved simultaneously but the mental status is normal, the appropriate diagnosis is a polysymptomatic CIS.
Algorithm for the classification of a first central nervous system (CNS) demyelinating attack. ADEM, acute disseminated encephalomyelitis; CIS, clinically isolated syndrome.
In 2010, the McDonald criteria for the diagnosis of multiple sclerosis (MS) in adults were revised and have since been adopted for the diagnosis of pediatric MS. For the first time, these criteria allowed for the diagnosis of MS at the time of the first clinical attack, provided that specific MRI features were present that showed dissemination in space and time. Although this approach appropriately allows for an earlier diagnosis of MS and initiation of prophylactic treatment, given the implications of a diagnosis of MS, these criteria should be applied only by clinicians with the requisite expertise. With these newer criteria, some pediatric patients with a CIS will meet criteria for MS.
Although the differential diagnosis varies somewhat ...