What is the most likely diagnosis for a patient with chronic diarrhea, abdominal pain, and hematochezia, with a history of axial spondyloarthropathy and anemia?

Ulcerative Colitis

The most likely diagnosis is ulcerative colitis (Option A), given the combination of chronic bloody diarrhea, bilateral lower abdominal pain, severe anemia, and the critical association with axial spondyloarthropathy. 1

Key Diagnostic Features Supporting Ulcerative Colitis

Clinical Presentation Triad

• Chronic bloody diarrhea (4 weeks duration) with intermittent blood is the hallmark presentation of UC, distinguishing it from acute infectious causes which typically resolve within 2-3 weeks 2
• Bilateral lower abdominal pain with bloody diarrhea represents the classic UC symptom complex 1, 2
• Progressive anemia (hemoglobin dropped from 12 to 7 g/dL over one year) with positive stool occult blood indicates chronic gastrointestinal blood loss from mucosal inflammation 1

Critical Association with Spondyloarthropathy

• Approximately 20% of UC patients develop peripheral or axial arthropathy, making this the second most common extraintestinal manifestation 1
• Patients with axial spondyloarthropathy (like this patient) have significantly higher incidence and prevalence of inflammatory bowel disease compared to the general population 1
• The discontinuation of etanercept several months ago is particularly relevant, as TNF inhibitors (excluding etanercept) are effective for both UC and axial spondyloarthropathy 1

Hemodynamic Instability Indicating Severe Disease

• Tachycardia (110 bpm) and relative hypotension (90/60 mmHg) with severe anemia requiring transfusion indicates moderate-to-severe UC 1
• The 5 g/dL hemoglobin drop over one year represents significant chronic blood loss from active colonic inflammation 1

Why Other Diagnoses Are Less Likely

Peptic Ulcer Disease (Option B) - Unlikely

• PUD typically causes epigastric pain, not bilateral lower abdominal pain 1
• While NSAIDs (ibuprofen 800mg) increase PUD risk, the 4-week duration of bloody diarrhea (not melena) and lower abdominal location argue against this 1
• PUD does not explain the association with axial spondyloarthropathy 1

Infectious Diarrhea (Option C) - Unlikely

• Infectious diarrhea rarely persists for 4 weeks without fever, and this patient is afebrile 1, 3
• The chronic progressive nature with worsening anemia over months to a year suggests chronic inflammatory disease rather than infection 3
• However, C. difficile must still be excluded in all new presentations of diarrhea regardless of antibiotic history before confirming IBD diagnosis 1, 3

Hemorrhoids (Option D) - Unlikely

• Hemorrhoids cause bright red blood on toilet paper or coating stool, not blood mixed with diarrhea 1
• Hemorrhoids do not cause chronic diarrhea, bilateral abdominal pain, or severe anemia requiring transfusion 1
• The systemic findings and association with spondyloarthropathy cannot be explained by hemorrhoids 1

Critical Diagnostic Pitfall: NSAID-Induced Colitis

A crucial consideration in this patient is NSAID-induced colonic pathology, given chronic ibuprofen use (800mg as needed) for spondyloarthropathy. 1

• NSAIDs are among the most common drug causes of chronic diarrhea and can cause colitis that mimics IBD endoscopically and histologically 1
• In elderly patients (though this patient's age is not specified), NSAIDs are specifically listed as a common IBD mimic requiring exclusion 1
• However, the strong association with axial spondyloarthropathy and the chronicity favor true UC over pure NSAID-induced pathology 1
• The distinction may be academic, as this patient likely has both UC (associated with spondyloarthropathy) and NSAID-exacerbated colitis 1

Immediate Diagnostic Workup Required

Mandatory Initial Testing

• Colonoscopy with biopsies from multiple sites is the gold standard and only definitive way to diagnose UC 1, 3, 2
• Stool culture and C. difficile toxin testing must be obtained before confirming IBD diagnosis 1, 3
• Complete blood count (already done), ESR or CRP, comprehensive metabolic panel, serum albumin, and ferritin to assess disease severity and iron deficiency 1
• Fecal calprotectin can help confirm intestinal inflammation if endoscopy is delayed 3

Expected Colonoscopic Findings in UC

• Continuous colonic inflammation starting from the rectum extending proximally with distinct demarcation between inflamed and non-inflamed bowel 2
• Erythema, loss of vascular pattern, granularity, erosions, friability, bleeding, and ulcerations 2
• Biopsies showing decreased crypt density, crypt architectural distortion, and heavy diffuse transmucosal inflammation without granulomas 2

Management Implications

Once UC is confirmed and infectious causes excluded, this patient will require aggressive therapy given the severe presentation with hemodynamic instability and transfusion-requiring anemia. 1, 2

• Hospitalization is appropriate for severe UC with hemodynamic compromise 2
• Intravenous corticosteroids are first-line for severe UC, with consideration of TNF-alpha antibodies (infliximab or adalimumab, NOT etanercept) if steroid-refractory 1, 2
• The previous use of etanercept for spondyloarthropathy is relevant because etanercept lacks efficacy for UC, while other TNF inhibitors (infliximab, adalimumab) effectively treat both conditions 1
• NSAIDs should be discontinued immediately, as they can exacerbate IBD and may have contributed to the current presentation 1