Differential Diagnosis for Right Lower Quadrant Pain

The patient's presentation of right lower quadrant pain with rebound tenderness suggests an acute abdominal process. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Acute Appendicitis: This is the most common cause of right lower quadrant pain, especially with rebound tenderness. The 5-day history of pain and the presence of rebound tenderness are classic signs that point towards appendicitis.

• Other Likely Diagnoses

  • Mesenteric Lymphadenitis: Inflammation of the lymph nodes in the mesentery can mimic appendicitis, especially in younger patients, but can occur at any age.
  • Right Ovarian Cyst or Torsion (in females): These conditions can cause severe lower abdominal pain and may present with rebound tenderness.
  • Intestinal Obstruction: Although less common, obstruction of the small or large intestine can cause abdominal pain and tenderness, potentially localized to the right lower quadrant.
  • Diverticulitis: Inflammation of a diverticulum in the colon, usually the sigmoid colon, but can occur in the cecum, presenting with right lower quadrant pain.

• Do Not Miss Diagnoses

  • Ectopic Pregnancy (in females): Although the patient is 50, it's still crucial to consider ectopic pregnancy in any female patient of childbearing age presenting with abdominal pain, as it is life-threatening.
  • Ruptured Abdominal Aortic Aneurysm: Although less common in non-hypertensive patients, a ruptured AAA can present with abdominal pain and is immediately life-threatening.
  • Perforated Visculitis (e.g., perforated ulcer): A perforation in the gastrointestinal tract can lead to peritonitis and severe abdominal pain.
  • Ovarian Tumor (in females): While less common, an ovarian tumor can cause abdominal pain and should be considered, especially if other diagnoses are ruled out.

• Rare Diagnoses

  • Right Lower Quadrant Pain due to Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease can cause chronic or acute abdominal pain but are less likely to present acutely with rebound tenderness.
  • Carcinoid Syndrome: A rare condition caused by a carcinoid tumor that can cause abdominal pain among other symptoms.
  • Abdominal Hemorrhage: Spontaneous bleeding into the abdominal cavity can cause pain and tenderness but is rare without trauma or anticoagulation.

Each diagnosis should be considered based on the patient's full clinical presentation, including laboratory results, imaging studies, and further history.