Which autoimmune disorder is characterized by antibody-mediated damage to acetylcholine receptors at the neuromuscular junction, causing progressive muscle weakness?

Which autoimmune disorder is characterized by antibody-mediated damage to acetylcholine receptors at the neuromuscular junction, causing progressive muscle weakness?

• A. Myasthenia gravis
• B. Lambert-Eaton syndrome
• C. Guillain-Barré syndrome
• D. Botulism

Answer: (A)

Autoimmune antibodies target postsynaptic acetylcholine receptors at the neuromuscular junction, reducing the number of functional receptors and impairing the muscle’s ability to respond to acetylcholine. This lowers the end-plate potential and makes transmission progressively weaker with use, producing fatigable muscle weakness that often starts with droopy eyelids and eye muscle weakness. This pattern is characteristic of myasthenia gravis, which may be associated with thymic abnormalities and can improve with rest or acetylcholinesterase inhibitors. Other conditions differ in where the problem lies: when the autoimmune attack is presynaptic, as in Lambert-Eaton syndrome, strength can improve with repeated use because more acetylcholine is released after sustained activity; Guillain-Barré syndrome involves immune-mediated nerve demyelination causing ascending paralysis; botulism blocks acetylcholine release rather than receptor function, leading to similar weakness but via a different mechanism.

Autoimmune antibodies target postsynaptic acetylcholine receptors at the neuromuscular junction, reducing the number of functional receptors and impairing the muscle’s ability to respond to acetylcholine. This lowers the end-plate potential and makes transmission progressively weaker with use, producing fatigable muscle weakness that often starts with droopy eyelids and eye muscle weakness. This pattern is characteristic of myasthenia gravis, which may be associated with thymic abnormalities and can improve with rest or acetylcholinesterase inhibitors.

Other conditions differ in where the problem lies: when the autoimmune attack is presynaptic, as in Lambert-Eaton syndrome, strength can improve with repeated use because more acetylcholine is released after sustained activity; Guillain-Barré syndrome involves immune-mediated nerve demyelination causing ascending paralysis; botulism blocks acetylcholine release rather than receptor function, leading to similar weakness but via a different mechanism.