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Myasthenia gravis is a chronic autoimmune neuromuscular disorder characterized by weakness and rapid fatigue of voluntary muscles. The condition results from antibodies blocking or destroying acetylcholine receptors at the neuromuscular junction, leading to impaired muscle contraction.
Autoantibodies primarily target acetylcholine receptors (AChR) at the postsynaptic membrane of the neuromuscular junction, though some patients have antibodies against muscle-specific kinase (MuSK) or lipoprotein-related protein 4 (LRP4). These antibodies reduce the number of functional receptors and impair neuromuscular transmission, resulting in progressive muscle weakness with repeated use.
Diagnosis involves assessing the characteristic pattern of fluctuating weakness that worsens with activity and improves with rest, particularly affecting ocular, bulbar, and proximal muscles. Key diagnostic tests include acetylcholine receptor antibody levels, electromyography showing decremental response to repetitive stimulation, and positive response to anticholinesterase medications like edrophonium or pyridostigmine.