What is the appropriate workup and potential missed diagnoses for an elderly male with a history of diverticulitis presenting with rectal bleeding and chronic diarrhea?

Workup and Can't-Miss Diagnoses for Elderly Male with Rectal Bleeding, Chronic Diarrhea, and Diverticulitis

Colonoscopy is mandatory and should be performed urgently in this patient—colorectal cancer must be excluded given the combination of rectal bleeding, chronic diarrhea, and age, as missed diagnoses of colorectal cancer should be <1% which cannot be achieved without direct visualization. 1

Immediate Laboratory Workup

Obtain the following blood tests immediately:

• Complete blood count to assess for anemia (from chronic bleeding) and leukocytosis (suggesting active inflammation or ischemia) 1, 2
• Serum albumin, ferritin, and C-reactive protein to evaluate nutritional status and systemic inflammation 1
• Liver enzymes and renal function to establish baseline for potential treatment toxicity monitoring 1
• Serum lactate as a marker of bowel ischemia and poor tissue perfusion 2
• Procalcitonin (PCT) which correlates with intestinal necrotic damage and mortality 2

Critical caveat: Only 50% of elderly patients with acute diverticulitis present with lower quadrant pain, 17% have fever, and 43% lack leukocytosis—normal labs do not exclude serious pathology. 3

Mandatory Stool Studies

• Clostridioides difficile testing is mandatory in all presentations of diarrhea in elderly patients, regardless of antibiotic history 1, 4
• Fecal calprotectin to assess for inflammatory bowel disease: values <50 μg/g effectively exclude IBD, while values >200-250 μg/g strongly suggest it 1, 4
• Stool culture and ova/parasites based on clinical features 4

Important pitfall: Do not rely on fecal calprotectin alone to exclude serious pathology—colonoscopy is still required even with normal values given cancer risk in elderly patients. 1

Imaging Requirements

CT scan with IV contrast is the first-line imaging study and should be performed in all elderly patients with suspected diverticulitis to confirm diagnosis, distinguish complicated from uncomplicated disease, and detect perforation, ischemia, or malignancy. 3, 2, 5

• Sensitivity 98-99%, specificity 99-100% for acute diverticulitis 5
• Detects bowel obstruction, perforation, peritonitis, ischemia, and colorectal malignancy 2

If IV contrast is contraindicated (severe renal disease or contrast allergy), use ultrasound, MRI, or CT without contrast as alternatives. 3

Can't-Miss Diagnoses in This Clinical Scenario

Highest Priority (Life-Threatening)

1. Colorectal cancer (60% of large bowel obstructions in elderly; presents with bleeding and altered bowel habits) 1, 2

2. Ischemic colitis (particularly with cardiovascular risk factors; presents with pain out of proportion to exam, bloody diarrhea) 1, 2

3. Complicated diverticulitis with perforation (elderly more likely to present with complicated disease; mortality up to 8%) 3, 2, 5

4. Acute mesenteric ischemia (mortality increases with every hour of delay; pain out of proportion to physical findings) 2

High Priority (Requires Specific Management)

1. Microscopic colitis (common cause of chronic diarrhea in elderly; requires histologic diagnosis from colonoscopy biopsies) 1

2. Segmental colitis associated with diverticulosis (SCAD) (can mimic inflammatory bowel disease; affects 1.15-11.4% of those with diverticulosis) 1, 6, 7

3. Late-onset inflammatory bowel disease (up to 15% of new IBD diagnoses occur after age 60) 1

4. NSAID-induced colonic pathology (common given NSAID use prevalence in elderly) 1

5. Radiation colitis (if history of pelvic radiation) 1

6. Large bowel obstruction from cancer or sigmoid volvulus (15-20% of large bowel obstructions from volvulus) 2

Colonoscopy Protocol

Timing and technique are critical:

• More than 90% of patients with chronic diarrhea over 45 years old should undergo colonoscopy 1
• Achieve cecal intubation rates >90% with terminal ileal intubation in >70% of cases if clinically indicated 1
• Obtain biopsies from both affected AND normal-appearing areas to detect microscopic colitis and other histologic diagnoses 1
• Delay colonoscopy 6 weeks after acute diverticulitis episode to reduce perforation risk, but do not delay if cancer is suspected 6, 5

Colonoscopy is mandatory after complicated diverticulitis, with atypical presentation, rectal bleeding, or diagnostic ambiguity. 6

Critical Clinical Assessment

Perform digital rectal examination to detect rectal mass, fecal impaction, blood, or rectal prolapse. 2

Examine all hernia orifices to detect incarcerated hernias. 2

Common Pitfalls to Avoid

• Do not assume normal CRP excludes active inflammation—15-20% of patients with active IBD have normal CRP 1, 4
• Do not delay colonoscopy for serial stool testing or empiric trials of therapy in elderly patients with new-onset symptoms 1
• Do not dismiss intermediate fecal calprotectin values (50-250 μg/g) without clinical correlation and endoscopic evaluation 1, 4
• Do not perform colonoscopy during acute diverticulitis—wait 6 weeks unless cancer is strongly suspected 8, 6

Disposition and Urgency

Immediate surgical consultation is required for:

• Hemodynamic instability despite resuscitation 2
• CT evidence of perforation, closed-loop obstruction, or bowel ischemia 2
• Peritoneal signs on examination 2

Hospital admission is indicated for:

• Inability to exclude surgical pathology 2
• Immunosuppression, intolerance to oral intake, severe sepsis, or significant comorbidities 5