Differential Diagnosis for Right Lower Quadrant Pain with Diarrhea and Mucus

Single Most Likely Diagnosis

• Appendicitis: This condition is a common cause of right lower quadrant pain and can be associated with changes in bowel habits, including diarrhea. The presence of mucus could indicate an appendiceal rupture or an appendiceal muccele, although these are less common presentations.

Other Likely Diagnoses

• Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic diarrhea, abdominal pain, and the passage of mucus. Right lower quadrant pain can be a feature, especially if the terminal ileum is involved.
• Diverticulitis: Although more common on the left side, diverticulitis can occur on the right and cause pain, changes in bowel habits, and potentially the passage of mucus if there is significant inflammation or infection.
• Gastroenteritis: Viral or bacterial infections can cause acute onset of diarrhea, abdominal pain, and sometimes the passage of mucus. The pain can be diffuse but may also be localized to the right lower quadrant.

Do Not Miss Diagnoses

• Intussusception: A condition where a part of the intestine telescopes into another, which can cause severe abdominal pain, diarrhea, and passage of mucus or blood. It's more common in children but can occur in adults, often with a lead point such as a tumor.
• Ectopic Pregnancy: Although typically presenting with pelvic pain and vaginal bleeding, an ectopic pregnancy can cause abdominal pain that might be perceived in the right lower quadrant, especially if the pregnancy is advanced or has ruptured.
• Mesenteric Ischemia: A condition where there's insufficient blood flow to the intestines, which can cause severe abdominal pain out of proportion to the physical examination, diarrhea, and potentially passage of mucus or blood if there's bowel infarction.

Rare Diagnoses

• Carcinoid Tumor: A type of neuroendocrine tumor that can cause diarrhea, abdominal pain, and flushing. If located in the small intestine, it could present with right lower quadrant pain.
• Lymphoma: Intestinal lymphoma can cause a variety of symptoms including abdominal pain, changes in bowel habits, and potentially the passage of mucus if there's significant involvement of the bowel wall.
• Meckel's Diverticulitis: A congenital anomaly of the small intestine that can cause inflammation and symptoms similar to appendicitis, including right lower quadrant pain and changes in bowel habits.