Myasthenia gravis is characterized by autoimmune destruction of acetylcholine receptors. Which statement best describes how this condition leads to weakness?

• A. Autoimmune destruction of acetylcholine receptors
• B. Decreased dopamine production
• C. Demyelination of peripheral nerves
• D. Increased intracranial pressure

Answer: (A)

Autoimmune destruction of acetylcholine receptors at the neuromuscular junction reduces the number of functional postsynaptic receptors. With fewer receptors, acetylcholine binding is less likely to produce a sufficient end-plate potential to reach the threshold needed to trigger a muscle action potential. The result is weaker muscle contractions that worsen with repeated use (fatigable weakness) and improve with rest or medications that increase acetylcholine availability. This mechanism directly explains the fatigable weakness seen in myasthenia gravis.

Others don’t fit because decreased dopamine points to extrapyramidal disorders like Parkinson disease; demyelination of peripheral nerves occurs in demyelinating neuropathies (e.g., Guillain-Barré syndrome) and affects nerve conduction; increased intracranial pressure involves CNS and presents with different signs.