A 30-year-old woman presents with bilateral ptosis and diplopia that worsen in the evening and with sustained use, and improve with rest. She has no atrophy. Ice pack test is positive. Repetitive nerve stimulation shows a decremental response at 3 Hz. Anti-acetylcholine receptor (anti-AChR) antibody is positive. Which pharmacological mechanism underlies the benefit of pyridostigmine in this condition?

• A Blocks voltage-gated calcium channels at the neuromuscular junction
• B Inhibits acetylcholinesterase, prolonging acetylcholine availability at the NMJ ✓
• C Binds to nicotinic receptors as a partial agonist
• D Reduces antibody production against AChR

Explanation

Myasthenia gravis is an autoimmune disorder characterized by antibodies against postsynaptic acetylcholine receptors (AChR), reducing functional receptor density and causing fatigable weakness. Pyridostigmine is an acetylcholinesterase inhibitor that prevents enzymatic breakdown of acetylcholine in the synaptic cleft, increasing its concentration and duration of action, thereby improving NMJ transmission. It provides symptomatic relief but does not alter the underlying autoimmune process; immunosuppression is required for long-term disease control.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.