What is the recommended imaging and diagnostic approach for a patient with chronic lower abdominal cramping and diarrhea for one month?

Diagnostic Approach for Lower Abdominal Cramping and Diarrhea for One Month

For a patient with chronic lower abdominal cramping and diarrhea lasting one month, the recommended initial diagnostic approach includes screening blood tests, stool studies, and colonoscopy with biopsies of the right and left colon to exclude inflammatory and neoplastic conditions before considering functional disorders. 1

Initial Evaluation

First-line Laboratory Tests

• Complete blood count (CBC)
• C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR)
• Comprehensive metabolic panel including electrolytes and liver function tests
• Thyroid function tests
• Iron studies
• Vitamin B12 and folate levels
• Celiac disease serology (anti-tissue transglutaminase IgA and total IgA) 1

First-line Stool Studies

• Fecal calprotectin (to detect inflammation)
• Fecal immunochemical test (FIT) for occult blood
• Stool culture and microscopy for infectious causes
• Clostridium difficile testing (especially if recent antibiotic use) 1, 2
• Stool for ova and parasites if indicated by history 1

Endoscopic Evaluation

Colonoscopy

• Colonoscopy with biopsies is strongly recommended for all patients with chronic diarrhea lasting more than one month 1
• Biopsies should be taken from both right and left colon (not just rectum) even if mucosa appears normal to exclude microscopic colitis 1
• Terminal ileal intubation and biopsy should be performed when Crohn's disease is suspected 1, 3
• For patients over 50 years, colonoscopy is particularly important to exclude colorectal neoplasia 1

Flexible Sigmoidoscopy

• May be considered as an alternative in younger patients (<45 years) with typical symptoms of functional bowel disorder and negative initial investigations 1
• However, full colonoscopy is preferred for chronic diarrhea to exclude proximal pathology 1

Additional Testing Based on Clinical Suspicion

For Suspected Bile Acid Diarrhea

• SeHCAT testing or serum 7α-hydroxy-4-cholesten-3-one measurement 1
• Consider empirical trial of bile acid sequestrants only after diagnostic testing 2

For Suspected Malabsorption

• Fecal elastase testing for pancreatic insufficiency 1
• Hydrogen breath testing for lactose maldigestion or small intestinal bacterial overgrowth 1

For Suspected Small Bowel Disease

• MR enterography is preferred over barium studies 1
• Video capsule endoscopy for suspected small bowel abnormalities 1

Diagnostic Algorithm

1. Initial assessment: Complete blood and stool tests as outlined above
2. If alarm features present (weight loss, nocturnal symptoms, blood in stool, age >50):
   • Proceed directly to colonoscopy with biopsies
3. If no alarm features but persistent symptoms:
   • Colonoscopy with biopsies still recommended to exclude microscopic colitis
4. If all initial tests negative:
   • Consider functional diagnosis (IBS-diarrhea or functional diarrhea)
   • Consider specialized testing for bile acid diarrhea, small intestinal bacterial overgrowth, or carbohydrate malabsorption

Common Pitfalls to Avoid

• Premature diagnosis of IBS: Always exclude inflammatory and neoplastic conditions before making a functional diagnosis 2
• Inadequate biopsies: Failure to take biopsies from both right and left colon can miss microscopic colitis 1, 2
• Missing terminal ileal disease: Failure to perform terminal ileal intubation when Crohn's disease is suspected 3
• Inadequate infection screening: Always perform stool cultures and C. difficile testing, especially in immunocompromised or elderly patients 1
• Overlooking medication causes: Many medications can cause chronic diarrhea; a thorough medication review is essential 1

Special Considerations

• For patients with suspected functional disorders, avoid repeated testing once organic pathology has been confidently excluded 4
• For patients with chronic bloody diarrhea, colonoscopy is mandatory regardless of age 2
• For patients under 40 years without rectal bleeding, fecal calprotectin can be used to exclude inflammation 1
• For patients over 45 years, colonoscopy is mandatory due to higher risk of colorectal neoplasia 1

By following this structured approach, clinicians can efficiently diagnose the cause of chronic lower abdominal cramping and diarrhea while minimizing unnecessary testing and delays in treatment.