Differential Diagnosis for Severe Left Lower Quadrant Abdominal Pain

The patient's presentation of severe left lower quadrant abdominal pain, without vomiting or nausea, while being treated for C. difficile infection (CDI) with fidaxomicin, requires a thorough evaluation. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Diverticulitis: This condition is a common cause of left lower quadrant abdominal pain. The patient's age and the sudden onset of severe pain without other symptoms like vomiting or nausea make diverticulitis a plausible diagnosis. The fact that the patient was improving from CDI does not rule out diverticulitis, as the two conditions can coexist or the antibiotics used for CDI could potentially contribute to the development of diverticulitis.

• Other Likely Diagnoses

  • Sigmoid Volvulus: Although less common than diverticulitis, sigmoid volvulus can cause severe abdominal pain and is more likely to present with vomiting. However, the absence of vomiting does not rule out this diagnosis.
  • Constipation: Severe constipation can cause significant abdominal pain, especially if there is an impaction. Given the patient's recent history of CDI and antibiotic use, constipation is a possible cause.
  • Ischemic Colitis: This condition can present with sudden onset of abdominal pain, typically in the left lower quadrant, and can be related to decreased blood flow to the colon. The patient's recent illness and potential for dehydration or low blood pressure could contribute to this condition.

• Do Not Miss Diagnoses

  • Appendicitis: Although appendicitis typically presents with right lower quadrant pain, it can occasionally present with left lower quadrant pain, especially if the appendix is retrocecal. Missing appendicitis can lead to severe consequences, including perforation and peritonitis.
  • Ectopic Pregnancy: In female patients of childbearing age, ectopic pregnancy must be considered, even if the pain is not typical. A pregnancy test should be performed to rule out this life-threatening condition.
  • Ovarian Torsion: This is another emergency that can present with severe lower abdominal pain. It requires immediate surgical intervention to preserve ovarian function.

• Rare Diagnoses

  • Inflammatory Bowel Disease (IBD) Flare: If the patient has a history of IBD (Crohn's disease or ulcerative colitis), a flare could present with severe abdominal pain. However, this would typically be accompanied by other symptoms like diarrhea or blood in the stool.
  • Colonic Intussusception: This is a rare condition where one part of the intestine slides into another, causing obstruction and potentially severe pain. It is more common in children but can occur in adults, often associated with a lead point like a tumor.

Investigations

• Imaging: CT scan of the abdomen and pelvis with contrast is the most useful initial imaging test for evaluating the cause of left lower quadrant abdominal pain, as it can help diagnose diverticulitis, sigmoid volvulus, ischemic colitis, and other conditions.
• Laboratory Tests: Complete blood count (CBC), basic metabolic panel (BMP), and lactate level to assess for signs of infection, inflammation, or ischemia.
• Pregnancy Test: In female patients of childbearing age to rule out ectopic pregnancy.
• Stool Tests: If diarrhea persists or recurs, stool tests for C. difficile toxin and other pathogens may be necessary.

Each of these diagnoses and investigations should be considered in the context of the patient's overall clinical presentation, medical history, and risk factors.