A 50-year-old man on pyridostigmine for myasthenia gravis reports increasing weakness and bulbar symptoms over three days. Intravenous edrophonium is administered and his weakness clearly improves within a minute. What is the correct interpretation and next step?

• A Cholinergic crisis, reduce pyridostigmine dose
• B Myasthenic crisis, increase anticholinesterase therapy ✓
• C Myasthenic crisis, stop all anticholinesterases immediately
• D Lambert-Eaton myasthenic syndrome, start guanidine

Explanation

Improvement of weakness after edrophonium indicates receptor blockade at the neuromuscular junction outstripping available acetylcholine, defining a myasthenic crisis, so anticholinesterase support should be increased. In a cholinergic crisis, extra acetylcholinesterase inhibition worsens weakness and produces muscarinic signs such as salivation, miosis and diarrhoea. In Lambert-Eaton the edrophonium response is poor because the defect is presynaptic calcium channel loss, reducing acetylcholine release itself.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.