A client is scheduled to have a Tensilon test. Which response to the test would confirm the diagnosis of myasthenia gravis?

• A. Brief exaggeration of symptoms
• B. Prolonged symptomatic improvement
• C. Rapid but brief symptomatic improvement
• D. Symptomatic improvement of only the ptosis

Answer: (C)

The key idea is that myasthenia gravis causes fatigable weakness due to impaired transmission at the neuromuscular junction, and a short-acting acetylcholinesterase inhibitor temporarily boosts acetylcholine availability to improve that transmission. When edrophonium (Tensilon) is given, if MG is present, there is a rapid improvement in muscle strength because the extra acetylcholine helps the already stressed receptors respond more effectively. However, this improvement is brief, lasting only for a short window while the drug’s effect wears off. That combination—quick onset and short duration of relief in affected muscles—is the classic positive sign used to support the diagnosis of MG.

Other patterns don’t fit as well: an exaggerated or worsening symptom isn’t produced by this drug, and a prolonged improvement isn’t expected given the fleeting action of the medication. Improvement limited to the eyelids can occur but isn’t the defining diagnostic sign; the hallmark is a rapid, short-lived boost in strength across fatigable muscles.