A 52-year-old man with myasthenia gravis (acetylcholine receptor antibody positive, generalised MG, MGFA Class IIb) fails pyridostigmine monotherapy. Prednisone is being considered for immunosuppression. Which of the following is the mechanism of benefit of pyridostigmine in MG?
- A Reversible inhibition of acetylcholinesterase, increasing synaptic acetylcholine concentration at the neuromuscular junction ✓
- B Blocking complement-mediated destruction of the postsynaptic membrane
- C Reducing acetylcholine receptor antibody production by B cells
- D Facilitating calcium-dependent vesicle release from presynaptic terminals
Explanation
Pyridostigmine is a reversible cholinesterase (acetylcholinesterase) inhibitor. By blocking the enzyme that degrades acetylcholine in the synaptic cleft, it increases the concentration and dwell time of ACh at the neuromuscular junction, partially compensating for the reduced number of functional AChR (due to antibody-mediated destruction and complement activation). It is symptomatic treatment only and does not modify the underlying autoimmune process. Eculizumab blocks complement (C5) and addresses the complement-mediated membrane destruction. Rituximab targets B cells and reduces antibody production. Calcium-channel facilitation is the mechanism of 3,4-diaminopyridine used in Lambert-Eaton syndrome.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.