This chapter discusses myasthenia gravis and myasthenic syndromes, and its related therapies. Myasthenia gravis (MG) and the myasthenic syndromes are diseases that affect the neuromuscular junction. In autoimmune MG, autoantibodies reduce the number of available acetylcholine receptors (AChRs), and thereby impair neuromuscular transmission. Initially, the most important clues to the diagnosis of MG were obtained from history and clinical examinations. The cardinal features of MG are weakness and fatigability of skeletal muscles, usually in a characteristic distribution. The weakness increases with activity and improves with rest. Typically, the signs and symptoms are more pronounced at the end of the day. The presenting symptoms vary from patient to patient, but in more than half of the cases, the initial complaints include diplopia and ptosis, often followed by difficulties in speech, chewing and swallowing, or by weakness of the upper and lower extremities. The distribution of muscle weakness is usually bilateral and is often proximal but may be asymmetrical and may involve different muscle groups over the course of the disease.
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