Differential Diagnosis for Tarry Black/Yellow Stool

• Single most likely diagnosis:
  • Gastrointestinal bleeding (upper GI bleed), specifically from the stomach or duodenum. This is because the black, tarry appearance (melena) is characteristic of digested blood that has been acted upon by gastric enzymes and intestinal bacteria, which is a common presentation of upper GI bleeding.
• Other Likely diagnoses:
  • Peptic ulcer disease: This condition can cause bleeding in the stomach or duodenum, leading to melena.
  • Gastritis: Inflammation of the stomach lining can lead to bleeding and melena.
  • Esophageal varices: Enlarged veins in the esophagus, often due to liver disease, can bleed and cause melena.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • Malignancy (e.g., stomach or esophageal cancer): Although less common, these conditions can cause GI bleeding and melena, and missing them could have severe consequences.
  • Aortic enteric fistula: A rare but potentially life-threatening condition where there's a connection between the aorta and the intestine, leading to severe bleeding.
  • Dieulafoy's lesion: A rare cause of GI bleeding from a mucosal defect with an exposed artery, which can present with sudden, severe bleeding.
• Rare diagnoses:
  • Hemobilia: Bleeding from the biliary tree into the GI tract, which can cause melena.
  • Hemosuccus pancreaticus: Bleeding from the pancreas into the GI tract, a rare cause of GI bleeding.
  • Angiodysplasia: Abnormal blood vessels in the GI tract that can cause bleeding, more common in the elderly.
  • Ingested blood (e.g., from nosebleed): Although not a GI source, ingested blood can mimic melena, especially if the amount is small and mixed with food or saliva.