American Board of Internal Medicine (ABIM) Certification Practice Exam

What percentage of patients with Myasthenia Gravis will test positive for acetylcholine receptor antibodies?

1. 100%

2. 80%

3. 90%

4. 70%

The correct answer is: 90%

In myasthenia gravis, a significant number of patients (approximately 85-90%) will test positive for acetylcholine receptor antibodies. These antibodies are directed against the nicotinic acetylcholine receptors at the neuromuscular junction and play a critical role in the pathophysiology of the disease, leading to the characteristic muscle weakness and fatigue experienced by patients. Testing for these antibodies is crucial for confirming the diagnosis of myasthenia gravis, particularly in cases where clinical symptoms are present but the diagnosis is uncertain. While not every patient will have these antibodies, the high percentage of positivity makes it a valuable tool in the diagnostic process. Other tests may include checking for muscle-specific kinase (MuSK) antibodies, which are present in a smaller proportion of patients who may be seronegative for acetylcholine receptor antibodies, but the majority of myasthenia gravis cases are indeed associated with the presence of acetylcholine receptor antibodies, solidifying the appropriateness of the selected response.