In myasthenia gravis, which statement best describes the autoimmune target and diagnostic tests with high specificity?

In myasthenia gravis, which statement best describes the autoimmune target and diagnostic tests with high specificity?

• A. Autoantibodies to acetylcholine receptors; fatigable weakness; positive anti-AChR antibodies or edrophonium test
• B. Autoantibodies to acetylcholine receptors; negative test
• C. Autoantibodies to dystrophin; constant weakness
• D. Autoantibodies to NMDA receptor; psychiatric symptoms

Answer: (A)

In myasthenia gravis, the autoimmune attack targets nicotinic acetylcholine receptors at the neuromuscular junction. This reduces the postsynaptic response to acetylcholine, leading to weakness that worsens with activity and improves with rest (fatigable weakness). For diagnosis with high specificity, two tests are most informative: detecting autoantibodies against the ACh receptor in the serum, and the edrophonium (Tensilon) test, where a short-acting acetylcholinesterase inhibitor briefly increases acetylcholine at the junction and transiently improves weakness. The combination of AChR-directed antibodies and a positive edrophonium response aligns with MG. By contrast, antibodies to dystrophin relate to muscular dystrophy, and NMDA receptor antibodies relate to autoimmune encephalitis with psychiatric symptoms; a negative test would not support the MG diagnosis.

In myasthenia gravis, the autoimmune attack targets nicotinic acetylcholine receptors at the neuromuscular junction. This reduces the postsynaptic response to acetylcholine, leading to weakness that worsens with activity and improves with rest (fatigable weakness). For diagnosis with high specificity, two tests are most informative: detecting autoantibodies against the ACh receptor in the serum, and the edrophonium (Tensilon) test, where a short-acting acetylcholinesterase inhibitor briefly increases acetylcholine at the junction and transiently improves weakness. The combination of AChR-directed antibodies and a positive edrophonium response aligns with MG. By contrast, antibodies to dystrophin relate to muscular dystrophy, and NMDA receptor antibodies relate to autoimmune encephalitis with psychiatric symptoms; a negative test would not support the MG diagnosis.