In suspected myasthenia gravis, which test helps confirm the diagnosis?

• A. MRD1 measurement
• B. Ice pack test or Tensilon test
• C. Pupils are normal
• D. Neck CT to rule out thymoma

Answer: (B)

When myasthenia gravis is suspected, the key is to demonstrate a reversible improvement in fatigable weakness due to enhanced neuromuscular transmission. The ice pack test and the Tensilon (edrophonium) test do this by boosting acetylcholine at the NMJ and showing a quick, measurable improvement.

The ice pack test is simple and safe. Apply a cold pack to the drooping eyelid for a few minutes; if ptosis improves, this supports MG involving the eyelid muscles because cooling slows acetylcholinesterase activity, increasing acetylcholine at the junction and improving transmission. This makes it a useful bedside confirmation for ocular MG.

The Tensilon test uses a short-acting acetylcholinesterase inhibitor to acutely raise acetylcholine levels. A brief, rapid improvement in muscle strength after administration strongly suggests MG, since the weakness stems from impaired nmj transmission rather than fixed muscle or nerve disease. However, it requires close monitoring due to potential cholinergic side effects, so its use varies by setting.

MRD1 measurement is helpful for documenting ptosis but does not confirm MG by itself. Normal pupils and imaging to look for thymoma are part of the broader workup, not confirmatory tests for MG.

So, the test that best confirms the diagnosis in this context is the ice pack test or the Tensilon test because both demonstrate improvement in neuromuscular transmission characteristic of myasthenia gravis.