A 55-year-old woman with myasthenia gravis on pyridostigmine presents with increasing generalised weakness. An edrophonium test is performed and her weakness transiently worsens. What does this indicate?

• A Myasthenic crisis requiring an increase in anticholinesterase dose
• B Cholinergic crisis caused by excess anticholinesterase therapy ✓
• C Thymoma-related deterioration requiring urgent thymectomy
• D Corticosteroid-induced myopathy unrelated to myasthenia gravis

Explanation

Edrophonium briefly inhibits acetylcholinesterase and increases acetylcholine at the neuromuscular junction. In myasthenic crisis, extra acetylcholine improves transmission and strength increases. In cholinergic crisis, the junction is already desensitised by excess agonist, so further acetylcholine accumulation deepens depolarisation blockade and the weakness worsens. A worsening response therefore mandates stopping or reducing the anticholinesterase and supporting ventilation rather than escalating the dose.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.