During a Tensilon test for myasthenia gravis, which symptom may accompany the sudden decrease in muscle strength?

During a Tensilon test for myasthenia gravis, which symptom may accompany the sudden decrease in muscle strength?

• A. Miosis
• B. Tachycardia
• C. Bronchodilation
• D. Constipation

Answer: (A)

When edrophonium is given in a Tensilon test, it increases acetylcholine at the neuromuscular junction. If too much acetylcholine accumulates, parasympathetic (muscarinic) effects dominate. A classic sign of this muscarinic overstimulation is pupil constriction, or miosis, due to stimulation of the iris sphincter. So a sudden decrease in muscle strength during the test may be accompanied by miosis. The other options don’t fit because they reflect sympathetic activity or opposite cholinergic effects (tachycardia is more like sympathetic drive, bronchodilation isn’t typical of cholinergic excess, and constipation would contradict the increased GI motility seen with excess acetylcholine).

When edrophonium is given in a Tensilon test, it increases acetylcholine at the neuromuscular junction. If too much acetylcholine accumulates, parasympathetic (muscarinic) effects dominate. A classic sign of this muscarinic overstimulation is pupil constriction, or miosis, due to stimulation of the iris sphincter. So a sudden decrease in muscle strength during the test may be accompanied by miosis. The other options don’t fit because they reflect sympathetic activity or opposite cholinergic effects (tachycardia is more like sympathetic drive, bronchodilation isn’t typical of cholinergic excess, and constipation would contradict the increased GI motility seen with excess acetylcholine).