A patient presents with black stools and a history of cirrhosis. What is the most likely cause of this symptom?

The presentation of black stools, also known as melena, indicates the presence of digested blood in the gastrointestinal tract. In the context of a patient with a history of cirrhosis, the most likely cause is esophageal varices. Cirrhosis often leads to portal hypertension, which can cause the formation of varices – swollen veins typically located in the esophagus or stomach. When these varices rupture, they can lead to significant bleeding, resulting in melena as the blood is digested by the gastrointestinal tract.

Peptic ulcer disease can certainly lead to similar symptoms; however, in a patient with cirrhosis, the occurrence of esophageal varices is a more immediate and common concern due to the physiological changes associated with liver disease. While gastritis could also be a cause of melena, it is less likely to result in the degree of bleeding seen with varices in patients with cirrhosis. Colon carcinoma, too, can present with changes in stool color, but given the context of liver disease, esophageal varices are a more prevalent cause of black stools in this scenario. Thus, esophageal varices distinctly align with the patient's history of cirrhosis and the symptom of black stools.