Question

Which drug is used to differentiate myasthenia gravis from cholinergic crisis?

• A. Pyridostigmine
• B. Edrophonium
• C. Methacholine
• D. Clonidine

Hint:

The short acting Tensilon (edrophonium) test diagnoses myasthenia.

Answer 1

The Correct Option is B

Step 1: The clinical problem is to distinguish a myasthenic crisis (too little acetylcholine effect) from a cholinergic crisis (too much, from anticholinesterase overdose).
Step 2: Edrophonium is a very short acting anticholinesterase used as the diagnostic Tensilon test for myasthenia, so option b is correct.
Step 3: The test: 2 mg is injected intravenously; if no reaction occurs in about 45 seconds, an additional 8 mg is given. In myasthenia gravis there is a brief improvement in muscle strength lasting about 5 minutes. In cholinergic crisis the weakness would worsen.
Step 4: Pyridostigmine (a) is a long acting agent used for maintenance therapy, not rapid diagnosis. Methacholine (c) is a muscarinic agonist and clonidine (d) is an alpha 2 agonist, so neither is used for this test.