What is Distal Colitis?
Distal colitis refers to inflammation of the colon confined to the rectum alone (proctitis) or the rectum and sigmoid colon (proctosigmoiditis), representing a subtype of ulcerative colitis that affects up to 60-80% of newly presenting cases. 1, 2
Anatomical Definition
The term "distal" specifically describes colitis limited to:
- Proctitis: inflammation confined to the rectum only 1
- Proctosigmoiditis: inflammation involving the rectum and sigmoid colon 1, 2
This distinguishes it from more extensive disease patterns, which include left-sided colitis (extending to the splenic flexure), extensive colitis (to the hepatic flexure), and pancolitis (involving the entire colon). 1
Key Pathological Characteristics
Distal colitis demonstrates diffuse, continuous mucosal inflammation that:
- Begins at the rectum and extends proximally without skip areas 1
- Remains superficial, affecting only the mucosa rather than transmural layers 1
- Shows characteristic crypt architectural distortion with branching and atrophy 1
- Lacks the granulomas and fissures typical of Crohn's disease 1
The transition between inflamed and normal mucosa is typically sharp, and the inflammation is continuous rather than patchy. 1
Clinical Significance
Distal colitis generally follows a milder clinical course than extensive disease:
- Symptoms are less severe than in patients with more extensive colonic involvement 2
- The disease is particularly amenable to topical therapy due to the accessible location 2, 3
- Most patients experience a benign course, though exacerbations with rectal bleeding can occur 4
- Extension of disease, cancer development, and surgical requirements are relatively unusual 4
Important Clinical Variants
A cecal or periappendiceal "patch" of inflammation can occur in left-sided disease:
- This discontinuous inflammation surrounding the appendiceal orifice occurs in up to 75% of patients with distal disease 1
- Patients with this pattern are younger (median age 31 vs 41 years) and more likely to show proximal disease extension (35.6% vs 10.0%) 5
- A small fraction (9.8%) may eventually be rediagnosed with Crohn's disease 5
- However, this pattern does not increase risk of neoplasia, colectomy, or need for pharmacotherapy escalation 5
Rectal sparing can occur in treated patients:
- Up to 44% of patients receiving topical or systemic treatment may show rectal sparing 1
- This therapy-related finding can create diagnostic confusion but does not change the underlying diagnosis 1
Common Diagnostic Pitfalls
Several factors can complicate accurate diagnosis:
- Concurrent enteric pathogens must be excluded before confirming inflammatory bowel disease 3
- In homosexual males, multiple other causes of proctitis exist beyond idiopathic ulcerative colitis 4
- Approximately 5% of patients with colonic IBD remain unclassifiable as "indeterminate colitis" despite full evaluation 1
- Perianal fistulae and abscesses are rare in distal ulcerative colitis and suggest Crohn's disease instead 4