All of the following are associated with carcinoid syndrome except: September 2005
**Core Concept**
Carcinoid syndrome is a clinical disorder caused by the excessive release of biogenic amines, such as serotonin (5-HT), histamine, and bradykinin, from neuroendocrine tumors, typically of the carcinoid type. These substances are produced by the tumor and lead to various systemic symptoms.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of carcinoid syndrome. The primary mechanism involves the release of serotonin, which is metabolized by the enzyme monoamine oxidase (MAO) in the liver. However, in patients with carcinoid syndrome, the liver is often bypassed due to right-sided heart failure or other liver dysfunction, allowing the serotonin to enter the systemic circulation and cause symptoms. The other options are all associated with carcinoid syndrome due to their direct or indirect involvement in its pathophysiology.
**Why Each Wrong Option is Incorrect**
**Option A:** Flushing is a classic symptom of carcinoid syndrome, caused by the release of serotonin and other vasoactive substances.
**Option B:** Diarrhea is another common symptom, resulting from the effect of serotonin on the gastrointestinal tract.
**Option C:** Wheezing is a symptom of carcinoid syndrome, related to the release of histamine and other substances that cause bronchoconstriction.
**Clinical Pearl / High-Yield Fact**
The presence of carcinoid syndrome should prompt a search for a primary tumor, as it is often a sign of metastatic disease. A thorough evaluation, including imaging studies and endoscopy, is essential to identify the tumor.
**Correct Answer: D.**