What are the causes of sigmoid colitis?

Causes of Sigmoid Colitis

Sigmoid colitis can be caused by inflammatory bowel disease (particularly ulcerative colitis), infections, ischemia, diverticular disease, and medications, with each having distinct clinical, endoscopic, and histological features that aid in diagnosis.

Inflammatory Bowel Disease

Ulcerative Colitis

• Characterized by diffuse mucosal inflammation starting in the rectum and extending proximally in a continuous pattern 1
• Histological features include:
  • Basal plasmacytosis
  • Diffuse crypt atrophy and distortion
  • Villous surface irregularity
  • Mucus depletion 1
• Continuous inflammatory process without skip areas 1
• Inflammation severity typically increases toward the rectum 1

Crohn's Disease

• Features patchy, transmural inflammation that can affect any part of the GI tract 1
• Histologically distinguished by:
  • Focal (discontinuous) inflammation
  • Transmural involvement
  • Presence of granulomas not related to crypt injury
  • Less common crypt abscesses compared to UC 1

Infectious Causes

Bacterial Infections

• Common pathogens include Clostridium difficile, Salmonella, Shigella, and pathogenic E. coli
• Always perform stool cultures and C. difficile toxin assay in suspected colitis 1
• Infectious colitis can be differentiated from IBD by:
  • Absence of basal plasmacytosis (present in only 6% vs. 63% in UC) 1
  • Acute self-limited course
  • Positive stool cultures or toxin assays 1

Cytomegalovirus (CMV) Colitis

• Can cause primary colitis or exacerbate existing IBD
• Diagnosed by typical CMV inclusions on biopsy 1
• May present with submucosal black nodules in the sigmoid colon 2
• Can trigger severe flares in patients with established UC 2

Ischemic Colitis

• Commonly affects the "watershed" territory from sigmoid colon to splenic flexure 1
• Endoscopic findings include:
  • Normal rectum (rectal sparing)
  • Sharply defined segments of involvement
  • Petechial hemorrhages
  • Longitudinal ulcerations
  • Rapid resolution on serial examinations 1
• More common in older patients with vascular risk factors

Diverticular Disease-Associated Colitis

Segmental Colitis Associated with Diverticulosis (SCAD)

• Inflammation confined to sigmoid colon harboring diverticula 3
• Characteristic features:
  • Patchy or confluent granularity and friability around diverticular ostia
  • Normal colonic mucosa proximal and distal to the sigmoid 3
  • Rectal sparing (normal rectal mucosa) 4
  • Histological features mimicking IBD 3
• Predominantly affects older adults, especially males 4
• Often self-limited or responsive to 5-aminosalicylates 4

Medication-Induced Colitis

• Various medications can cause colonic inflammation
• Common culprits include NSAIDs, antibiotics, and chemotherapeutic agents
• Diagnosis relies on temporal relationship between drug initiation and symptom onset
• Usually resolves with discontinuation of the offending agent

Diagnostic Approach

1. Endoscopic evaluation with biopsies is essential for diagnosis and excluding other causes 1
2. Stool testing for infectious agents, including C. difficile toxin assay 1
3. Histological assessment to differentiate between causes:
   • Continuous vs. discontinuous inflammation
   • Presence of granulomas
   • Basal plasmacytosis
   • Crypt architecture distortion 1

Important Considerations

• Symptoms lasting more than 14 days with unidentified causes should prompt consideration of non-infectious conditions like IBD 1
• Endoscopic appearance during acute colitis may help determine the pattern of inflammation pointing toward UC or Crohn's 1
• Some conditions may mimic or overlap with IBD, making diagnosis challenging 5
• In patients with established IBD, superimposed infections (particularly C. difficile and CMV) should be ruled out during flares 1

Remember that accurate diagnosis is crucial as treatment approaches differ significantly between the various causes of sigmoid colitis, with implications for long-term management and prognosis.