American Board of Internal Medicine (ABIM) Certification Practice Exam

What malignancy is most commonly associated with Lambert-Eaton Myasthenic Syndrome?

1. Breast cancer

2. Colon cancer

3. Small cell lung cancer

4. Prostate cancer

The correct answer is: Small cell lung cancer

Lambert-Eaton Myasthenic Syndrome (LEMS) is an autoimmune condition characterized by weakness and fatigue resulting from defective communication between nerves and muscles. One of the key associations found in medical literature is its strong link with small cell lung cancer (SCLC). This connection is primarily due to the production of anti-voltage-gated calcium channel antibodies which disrupt neuromuscular transmission, leading to the symptoms typical of LEMS. Small cell lung cancer, often associated with paraneoplastic syndromes like LEMS, is a neuroendocrine tumor and is known for its aggressive nature and strong correlation with various neurological complications. The mechanism behind this association typically involves the immune system's response to the malignancy, which may manifest as the production of antibodies that impair neuromuscular function. In contrast, while other malignancies like breast, colon, and prostate cancers are significant in their own right, they exhibit a weaker or nonspecific association with LEMS. More specifically, breast cancer may be linked with various autoimmune disorders, but it is not the prevalent malignancy correlated with LEMS as is small cell lung cancer. This distinctive association highlights the importance of recognizing underlying malignancies in patients presenting with signs and symptoms of LEMS, making early