What is the differential diagnosis (DDX) of erosive rectosigmoiditis?

Differential Diagnosis of Erosive Rectosigmoiditis

The differential diagnosis of erosive rectosigmoiditis includes ulcerative colitis (most common when inflammation is continuous from the rectum), infectious colitis (Salmonella, Shigella, Campylobacter, C. difficile, CMV), ischemic colitis (particularly in elderly with vascular disease), medication-induced colitis (NSAIDs, chemotherapy), Crohn's disease (when skip lesions present), and less commonly Behçet's disease, eosinophilic colitis, or immunodeficiency-related colitis. 1

Primary Inflammatory Bowel Disease

Ulcerative colitis is the leading diagnosis when inflammation is continuous and confluent, extending proximally from the rectum with clear demarcation. 1 Rectal involvement occurs in more than 97% of untreated ulcerative colitis cases. 1 The disease remains localized to the rectosigmoid in approximately 90% of patients with proctosigmoiditis, with only 10% developing proximal extension over time. 2

Key distinguishing features include:

• Mucosal-only inflammation with diffuse basal plasmacytosis on histology 1
• Crypt architectural distortion and mucosal atrophy developing after 4 weeks of symptoms 1
• Absence of perianal disease (perianal fistulae and abscesses are rare in distal ulcerative colitis) 3

Crohn's disease should be considered when skip lesions, transmural inflammation, or perianal disease are present. 4 Crohn's disease is characterized by patchy, transmural inflammation that may affect any part of the gastrointestinal tract. 4

Infectious Etiologies

Obtain stool cultures and C. difficile toxin assay before diagnosing IBD, as Salmonella, Shigella, and Campylobacter can produce endoscopic features identical to ulcerative colitis. 1 Yersinia and cytomegalovirus enterocolitis can resemble Crohn's disease. 1

Critical distinguishing features:

• Infectious colitis typically shows preserved crypt architecture with acute inflammation only 1
• Acute symptoms (<2 weeks duration) suggest infection or ischemia 5
• Travel history or immunosuppression raises suspicion for parasitic infections (Giardia, Entamoeba) 5

In one study of erosive/ulcerative lesions, two patients initially showing acute nonspecific inflammation were later diagnosed with Crohn's disease, emphasizing the need for careful follow-up when symptoms persist. 6

Ischemic Colitis

Ischemic proctosigmoiditis is a critical differential, particularly in elderly patients with atherosclerosis and vascular risk factors. 1, 7 Although rectal ischemia is rare due to excellent collateral blood supply, isolated ischemic proctosigmoiditis does occur. 7

Distinguishing characteristics:

• Affects elderly patients with atherosclerosis 7
• Often has identifiable precipitating factors such as major illness, hemodynamic disturbance, or hypotension 7
• CT reveals rectal wall thickening and/or perirectal stranding 7
• Angiography may demonstrate atheromatous disease of aortoiliac vessels 7
• Typically affects watershed areas 1

Recognition and differentiation from idiopathic inflammatory bowel disease is critical because treatment differs—conservative management for acute ischemic proctosigmoiditis versus immunosuppression for IBD. 7

Medication-Induced Colitis

NSAIDs, immunosuppressants, and chemotherapy agents can cause erosive colitis, making medication history critical. 1 These agents should be discontinued if identified as the causative factor.

Less Common Etiologies

• Behçet's disease can present with erosive rectosigmoiditis 6
• Eosinophilic colitis 6
• Common variable immunodeficiency disease can cause severe rectosigmoidal colitis with transmural inflammation and macrophage predominance 8

Diagnostic Approach

Perform complete ileocolonoscopy with biopsies from at least five sites, taking at least two biopsies per site, even from normal-appearing mucosa. 1 This is essential because most erosive/ulcerative lesions show nonspecific inflammation histologically (84% in one study). 6

Critical documentation includes:

• Lesion distribution, rectal involvement, and presence of skip lesions 1
• Biopsies from both inflamed and uninflamed segments 1
• Look for granulomas (Crohn's), basal plasmacytosis (UC), preserved crypt architecture (infection), or eosinophilic infiltration 1

Obtain complete blood count, CRP, albumin, liver function, iron studies, and renal function. 1 Fecal calprotectin >100 μg/g supports IBD diagnosis with 93% sensitivity and 96% specificity. 1

Perform cross-sectional imaging (CT or MR enterography) to evaluate small bowel involvement and complications. 1 MR enterography is preferred in young patients to avoid radiation. 5

Common Pitfalls

Careful follow-up is required when symptoms and/or lesions do not improve, as initial nonspecific findings may evolve into definitive IBD. 6 Do not assume ulcerative colitis without excluding infectious causes first. 1 In elderly patients with vascular risk factors, always consider ischemic colitis to avoid inappropriate immunosuppression. 7