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This chapter provides a practical approach, to the evaluation and treatment of the most common pediatric-acquired neuromuscular transmission disorder, myasthenia gravis.

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Thomas Willis is credited with the 17th century description of myasthenia gravis (MG).1-3 In 1879 Erb elaborated on the characteristic MG clinical syndrome.3Jolly followed in 1895, reporting a 14-year-old boy with varying ptosis, oropharyngeal, and generalized muscle weakness suggested the term myasthenia gravis pseudoparalytica.4 Important investigations in the 1930s included physostigmine’s symptomatic efficacy5 and the chemical basis of neuromuscular transmission.6 Specific EMG features of MG were reported in 1941.7

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An association of 2 previously recognized autoimmune disorders, namely thyroiditis and pernicious anemia, sometimes occurring concomitantly in MG patients, provided the basis for the proposed autoimmune basis of MG.8Acetylcholine was next identified as the primary neuromuscular junction neurotransmitter.9 In 1973 an experimental allergic myasthenia gravis with clinical, pharmacologic, and EMG equivalence to human MG was discovered.10 Subsequently, acetylcholine receptor antibodies were identified in human MG.11 (See eFigs. 571.1, 571.2.) Positive therapeutic responses to plasmapheresis supported myasthenia gravis’s autoimmune nature.12 Testing for acetylcholine antibodies is the most valuable current means to diagnose the disease.13-15

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eFigure 571.1.
Graphic Jump Location

Schematic of neuromuscular junction from Drachmann NEJM 1980+/– NEJM 1980+/ Drachman NEJM 1980+/– Drachman.

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eFigure 571.2.
Graphic Jump Location

Neuromuscular junction. The primary molecular antigenic site of the postsynaptic ACh receptor: Drachman NEJM 1980+/–. NEJM 1980+/– Drachman NEJM 1980 +/– Drachman.

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Most (85%) MG patients have antibodies against the nicotinic acetylcholine receptors (AChR) at skeletal muscle end plates. Another antibody-specific tyrosine kinase (muscle-specific kinase) is found in 50% of MG patients who are AChR antibody negative.16,17 These various antibodies damage and reduce the number of AChRs. Thymic hyperplasia occurs in many adult MG patients; a benign thymoma is present in 10% of adults. In contrast, this is an extremely uncommon occurrence in children.

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Myasthenia gravis (MG) is the most common neuromuscular transmission disorder in children and adults. Young children typically present with ocular MG manifested by ptosis and or diplopia.18Generalized MG presents with varied combinations of ocular, bulbar, neck, and limb weakness, and, rarely, respiratory distress, and is more common in adolescents.17Neonatal myasthenia gravis occurs in 15% of babies born to mothers with autoimmune MG.19 Congenital myasthenia gravis syndromes are a group of widely differing, much less-common neuromuscular transmission disorder, each characterized by compromised neuromuscular transmission safety margin.20 These genetically determined myasthenic disorders generally present during the first years of life with a more subtle ptosis and extraocular weakness. In contrast, other variants may have a very acute presentation, with the baby in extremis with a sudden ...

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