A 32-year-old female presents with progressive muscle weakness, diplopia, and ptosis that worsens toward the evening and improves after rest. Repetitive nerve stimulation testing reveals decremental motor response. What serum autoantibody is most commonly detected?

Answer and explanation

Correct answer: D. Anti-acetylcholine receptor (AChR) antibodies

  1. Step 1: Fatigable muscle weakness, fluctuating ptosis, and diplopia worse with exertion is classic for Myasthenia Gravis (MG).
  2. Step 2: Approximately 85% of patients with generalized myasthenia gravis possess circulating autoantibodies directed against the nicotinic acetylcholine receptor (AChR) at the postsynaptic neuromuscular junction.
  3. Step 3: VGCC antibodies characterize Lambert-Eaton myasthenic syndrome; anti-GM1 antibodies are associated with Guillain-Barre syndrome.
Answer
Anti-acetylcholine receptor (AChR) antibodies.
Why not the others: Anti-VGCC is Lambert-Eaton; anti-MOG is demyelinating disease; anti-GM1 is Guillain-Barre.

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