What is the appropriate workup and treatment for a 60-year-old female with 2 weeks of left lower quadrant abdominal pain and 2-3 episodes of liquid diarrhea daily, without blood, and a clean colonoscopy 6 months ago, with no fever?

Workup and Treatment for 60-Year-Old Female with Left Lower Quadrant Pain and Diarrhea

This patient requires targeted infectious and inflammatory workup followed by empiric treatment for diarrhea-predominant IBS if testing is negative, given the recent clean colonoscopy excludes structural disease. 1

Immediate Workup

Laboratory Studies:

• Complete blood count to exclude anemia and assess for leukocytosis 1
• Erythrocyte sedimentation rate and serum chemistries/albumin to evaluate for inflammatory processes 1
• Stool studies: C. difficile toxin, ova and parasites, fecal occult blood, and bacterial culture (including Aeromonas species) 1, 2
• Consider celiac serologies given the diarrhea-predominant presentation 1

Imaging:

• CT abdomen/pelvis with IV contrast is not immediately indicated given the clean colonoscopy 6 months ago, absence of fever, and no red flags 1, 3
• Reserve CT for development of fever, peritoneal signs, inability to pass gas/stool, bloody stools, or worsening symptoms 3

Differential Diagnosis Priority

Most Likely Diagnoses:

• Irritable bowel syndrome (diarrhea-predominant) - most probable given symptom pattern and recent normal colonoscopy 1, 3
• Infectious colitis (C. difficile, parasites, bacterial) - must exclude before functional diagnosis 1
• Microscopic colitis - consider if stool studies negative and symptoms persist 1
• Early/atypical diverticulitis - less likely given no fever, but possible 3, 4

Treatment Algorithm

If Stool Studies Positive:

• Treat specific pathogen identified (e.g., metronidazole or vancomycin for C. difficile, appropriate antibiotics for bacterial pathogens) 5, 2

If All Testing Negative (Presumed IBS):

• Initiate empiric loperamide for diarrhea control as first-line therapy 1
• Trial of antispasmodic medication (e.g., dicyclomine, hyoscyamine) for pain relief 1
• Dietary modifications: consider lactose-free diet trial and assess for food triggers 1
• Patient education and reassurance about benign nature of functional bowel disorder 1

Follow-Up and Escalation

Reassess in 3-6 weeks: 1

• If symptoms improve, continue current management
• If refractory, consider flexible sigmoidoscopy with biopsies to exclude microscopic colitis 1
• Gastroenterology referral for persistent symptoms despite conservative measures 3

Red Flags Requiring Immediate Re-evaluation:

• Development of fever, bloody stools, weight loss, or severe tenderness with guarding mandates urgent CT and possible hospitalization 3, 6, 7