A 30-year-old female presents with severe generalized muscle weakness that worsens toward the end of the day and improves with rest. On exam, she has bilateral ptosis and diplopia. Edrophonium test temporarily relieves symptoms. What is the underlying pathophysiology?

Answer and explanation

Correct answer: B. Autoantibodies against postsynaptic nicotinic acetylcholine receptors (AChR)

  1. Step 1: Recognize myasthenia gravis, an autoimmune neuromuscular junction disorder.
  2. Step 2: Pathogenic IgG autoantibodies bind and block postsynaptic nicotinic acetylcholine receptors (AChR) on the motor end plate, causing receptor internalization and complement-mediated destruction.
  3. Step 3: Fluctuating fatiguable muscle weakness involving ocular, bulbar, and proximal limb muscles is characteristic.
Answer
Autoantibodies against postsynaptic nicotinic acetylcholine receptors (AChR).
Why not the others: 'Autoantibodies against presynaptic voltage-gated calcium channels' describes Lambert-Eaton myasthenic syndrome, where strength improves with repeated exertion; 'Demyelination of peripheral motor nerve axons' describes Guillain-Barre syndrome; 'Degeneration of anterior horn cells in the spinal cord' describes amyotrophic lateral sclerosis (ALS).

Practise more Internal Medicine and Therapeutics.

Free questions with an explanation for every one, and full timed Oman Medical Specialty Board Examination (OMSB) mock tests.

All Internal Medicine and Therapeutics questionsTake a mock test

More Internal Medicine and Therapeutics questions