What is the most likely diagnosis for a 57-year-old woman with sudden diarrhea, facial flushing, and left lower lobe atelectasis?

The most likely diagnosis in this scenario is a carcinoid tumor. Carcinoid tumors are neuroendocrine tumors that often arise in the gastrointestinal tract, particularly in the appendix and small intestine, but can also occur in other areas. They can lead to flushing episodes, which is a characteristic symptom due to excessive secretion of serotonin or other vasoactive substances.

In this case, the sudden onset of diarrhea, facial flushing, and left lower lobe atelectasis suggests a systemic effect of the tumor, likely due to carcinoid syndrome. The diarrhea is consistent with increased serotonin levels, which can lead to increased bowel motility. The facial flushing occurs as a result of vasodilation induced by the substances secreted by the tumor. The left lower lobe atelectasis may be related to bronchial obstruction or an indirect effect due to a potential mediastinal mass or hilar involvement.

Other options do not align as closely with the combination of symptoms presented. While angioedema involves swelling and could potentially cause flushing, it doesn’t explain the diarrhea or atelectasis. Cardiac dysrhythmias could present with flushing but would not typically cause diarrhea or atelectasis. Irritable bowel syndrome can lead to diarrhea but would