American Board of Internal Medicine (ABIM) Certification Practice Exam

What is a characteristic antibody finding in Lambert-Eaton Myasthenic Syndrome?

1. Anti-acetylcholine receptor antibodies

2. Anti-voltage-gated calcium channel antibodies

3. Anti-MuSK antibodies

4. Anti-nuclear antibodies

The correct answer is: Anti-voltage-gated calcium channel antibodies

Lambert-Eaton Myasthenic Syndrome (LEMS) is primarily characterized by the presence of antibodies against voltage-gated calcium channels (VGCC). This autoimmune condition leads to a reduction in the release of acetylcholine at the neuromuscular junction due to impaired calcium influx, which is critical for neurotransmitter release. The formation of these antibodies is typically associated with underlying malignancies, especially small cell lung cancer. In contrast, anti-acetylcholine receptor antibodies are mainly associated with Myasthenia Gravis, while anti-MuSK antibodies can also be involved but are specific to a different variant of myasthenia. Anti-nuclear antibodies are primarily associated with systemic lupus erythematosus and other autoimmune disorders, not specifically with Lambert-Eaton Myasthenic Syndrome. Therefore, the detection of anti-voltage-gated calcium channel antibodies is a key diagnostic marker for identifying LEMS and understanding its pathophysiology.