Myasthenia Gravis

(Samter’s Ch. 51)

• Neuromuscular disorder characterized by weakness and fatigability of skeletal muscles

• decrease in the number of available nicotinic acetylcholine receptors (AChRs) at neuromuscular junctions due to an antibody-mediated autoimmune attack

• 200–400 cases per million (one of the less common autoimmune disorders)• Current treatment highly effective; a specific cure remains elusive• USA: prevalence = 14.2 cases/1 million• Appear at any age• women: onset 20 - 40 years of age• men, at 40-60• (women : men = 3:2)• Familial occurrence is rare

• Annual incidence: 0.25-2/100,000• Spontaneous remission: 20%• Without treatment, 20-30% die in 10 years• Heterogeneous disorder• – 90% no specific cause• Genetic predisposing factor: HLA association; HLA-BW46 in chinese ocular

MG • 75%: thymus abnormal• – 65%: hyperplasia• – 10%: thymoma, rarely in children; often (20%) in patients aged 30-40 years

NEJM 1994, 1997 Neurologic Clinics 1997; BJA 2002JOAO 2004

• Lambert-Eaton Myasthenic Syndrome• Drug-induced Myasthenic Syndromes• Congenital Myasthenic Sybdromes• Myasthenic Syndromes associated with

denervation