American Board of Internal Medicine (ABIM) Certification Practice Exam

What characteristic finding aids in the diagnosis of Myasthenia Gravis?

1. Positive throat culture

2. Acetylcholine receptor antibodies

3. Low serum calcium levels

4. Electrocardiogram abnormalities

The correct answer is: Acetylcholine receptor antibodies

Myasthenia gravis is an autoimmune neuromuscular disorder characterized by varying degrees of weakness of the skeletal muscles. The hallmark of this condition is the presence of antibodies that interfere with the transmission of nerve impulses to muscles. The most characteristic and diagnostic finding in patients with myasthenia gravis is the presence of acetylcholine receptor antibodies. These antibodies bind to receptors at the neuromuscular junction, preventing acetylcholine from attaching and leading to muscle weakness. Detection of acetylcholine receptor antibodies is a key diagnostic tool. In many cases, the presence of these antibodies can be confirmed by a blood test, which greatly aids in establishing the diagnosis of myasthenia gravis. Additionally, their presence correlates with the severity of muscle weakness, making this finding particularly relevant. Other choices do not fulfill the diagnostic criteria for myasthenia gravis. A positive throat culture pertains to infections, which is unrelated to the manifestations of myasthenia gravis. Low serum calcium levels may suggest other metabolic issues but are not associated with this neuromuscular disorder. Electrocardiogram abnormalities are more often related to cardiac conditions and do not provide appropriate information specific to myasthenia gravis. Thus, the