Myasthenia Gravis (from Greek μύς “muscle”, ἀσθένεια “weakness”, and Latin: gravis “serious”; abbreviated MG) is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigue. Muscle weakness is caused by circulating antibodies that block acetylcholine receptors at the postsynaptic neuromuscular junction, inhibiting the excitatory effects of the neurotransmitter acetylcholine on nicotinic receptors at neuromuscular junctions.
Myasthenia is treated medically with acetylcholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. The disease incidence is 3–30 cases per million per year and rising as a result of increased awareness. MG must be distinguished from congenital myasthenic syndromes that can present similar symptoms but do not respond to immunosuppressive treatments.