USMLE® Step 1 Question of the Day: Somatostatin analog

Test your knowledge with this USMLE Step 1 Question of the Day! A 50-year-old woman presents with daily diarrhea, skin flushing, and shortness of breath. She is treated with a somatostatin analog. Which medication was provided?

A 50-year-old woman comes to the physician to evaluate diarrhea and skin flushing. The patient has had almost daily episodes of diarrhea, which sometimes awaken her at night. She also notices that her skin turns red every time she drinks alcohol, and these episodes last around 20 minutes. The patient has also experienced intermittent shortness of breath and wheezing, which she attributes to seasonal allergies. Past medical history is notable for hypertension, anxiety, and seasonal allergies. She has had irregular menstrual cycles for the past four months. She does not take any medications. Vitals are within normal limits. Physical examination is noncontributory. The patient is provided a somatostatin analog for treatment. Which of the following medications was provided? 

A. Octreotide

B. Glucagon

C. Growth hormone 

D. Diphenhydramine 

E. Aspirin  

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The correct answer to today's USMLE® Step 1 Question is...

A. Octreotide

Before we get to the Main Explanation, let's look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!

Incorrect answer explanations

B. Glucagon 

Incorrect: Glucagon is the primary catabolic hormone in the body, it is not a somatostatin analog.

C. Growth hormone 

Incorrect: Growth hormone is not a somatostatin analog, nor is it used to treat patients with carcinoid syndrome.  

D. Diphenhydramine 

Incorrect: Diphenhydramine is a first-generation antihistamine. Although diphenhydramine can treat seasonal allergies, this medication is not used to treat carcinoid syndrome. 

E. Aspirin 

Incorrect: Aspirin can be used to manage flush associated with niacin use. Aspirin, however, has no role in the management of carcinoid syndrome.  

Main Explanation

Carcinoid tumors are neuroendocrine tumors that arise from enterochromaffin cells. They most often occur in the small intestines but can also develop in the appendix, pancreas, and lungs. 

Carcinoid tumors produce excess serotonin. Most serotonin is transported to the liver via portal circulation and broken down by first-pass hepatic metabolism. Therefore, the serotonin does not reach the systemic circulation to cause symptoms. However, carcinoid syndrome develops when serotonin escapes first-pass hepatic metabolism and enters the systemic circulation, such as when cancer metastasizes to extraintestinal sites (e.g. liver).  

Clinical features of carcinoid syndrome are due to serotonin’s effects on various tissues. Serotonin stimulates gut motility in the gastrointestinal tract, resulting in secretory diarrhea. In the skin, serotonin’s vasodilatory effects cause skin flushing, lasting anywhere from 30 seconds to 30 minutes. The flushing can be precipitated by emotional or physical stress and alcohol use. In the lungs, serotonin causes bronchoconstriction, leading to wheezing and dyspnea. Finally, serotonin stimulates fibroblast growth in cardiac tissues, resulting in plaque-like fibrous deposits on the valves, cardiac chambers, and major vessels. These cardiac effects are mainly seen in the right heart and can lead to heart failure and valvular disease. 

Histologically, carcinoid tumor cells are arranged in trabeculae or nests. Cells have eosinophilic cytoplasm and round/oval nuclei filled with fine granules. Like many other neuroendocrine tumors, immunostaining is positive for chromogranin and synaptophysin. 

Carcinoid syndrome can be treated with surgical resection and somatostatin analogs, such as octreotide. Somatostatin receptors are highly expressed in the tumor cells. As a result, somatostatin analogs can control symptoms, reduce tumor growth, and improve patient survival. 

Major Takeaway

Carcinoid syndrome is caused by excess serotonin production by a carcinoid tumor. Clinical symptoms may include diarrhea, intermittent skin flushing, wheezing, dyspnea, and heart failure. The condition can be treated with surgical resection and somatostatin analogs, such as octreotide. 

References

Cingam, S.R., Kashyap, S., Karachi, H. (2020) “Carcinoid tumors”. StatPearls [Internet]. Web Address: https://www.ncbi.nlm.nih.gov/books/NBK448101/.  

Pinchot, S.N., Holen, K., Sippel, R.S., Chen, H. (2008) Carcinoid tumors. The Oncologist. 13(12), 1255-1269. Doi: 10.1634/theoncologist.2008-0207. 

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