Differential Diagnosis for Mucous Bloody Stool with Left Upper Quadrant Pain

Single Most Likely Diagnosis

• Diverticulitis: This condition is characterized by inflammation of the diverticula in the colon, which can cause left lower quadrant pain, but can sometimes radiate to the left upper quadrant. The presence of mucous bloody stool supports this diagnosis, as diverticulitis can lead to bleeding and mucous production.

Other Likely Diagnoses

• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause bloody stools and abdominal pain. While the pain is typically more widespread or in the lower quadrants, it can sometimes be felt in the left upper quadrant.
• Ischemic Colitis: Reduced blood flow to the colon can cause abdominal pain, bloody stools, and mucous. The pain can be localized to the left upper quadrant if the ischemia affects the splenic flexure.
• Gastrointestinal Infection: Certain infections, such as those caused by Salmonella or Shigella, can lead to bloody stools and abdominal pain. The pain can sometimes be referred to the left upper quadrant.

Do Not Miss Diagnoses

• Intestinal Obstruction: Although less common, an obstruction in the intestines can cause severe abdominal pain and bloody stools if there is associated ischemia. This is a medical emergency.
• Colon Cancer: While less likely in younger patients, colon cancer can cause bloody stools and abdominal pain. It's crucial not to miss this diagnosis due to its significant implications for treatment and prognosis.
• Mesenteric Ischemia: This condition involves insufficient blood flow to the intestines and can cause severe abdominal pain out of proportion to physical examination findings, along with bloody stools. It is a medical emergency.

Rare Diagnoses

• Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause gastrointestinal bleeding and abdominal pain, though it's more commonly associated with the right lower quadrant.
• Intussusception: A condition where a part of the intestine telescopes into another part, which can cause abdominal pain and bloody stools. It's rare in adults but can occur.
• Henoch-Schönlein Purpura (HSP): A systemic vasculitis that can cause abdominal pain, gastrointestinal bleeding, and sometimes bloody stools. It's more common in children but can occur in adults.