Radiation colitis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Qasim Salau, M.B.B.S., FMCPaed [2]

Synonyms and keywords:

Overview

Radiation therapy is a common treatment modality for Abdominal and pelvic malignancy. Radiation colitis may complicate this radiotherapy. Radiation colitis tends to develop insidiously and it is often progressive.

Pathophysiology

• Occur following radiation therapy for Abdominal and pelvic malignancies .
• More common with radiation doses higher than 45Gy.
• The main site of damage is the DNA, inhibiting mitosis. May also affect RNA, proteins and cell membranes.
  • Injury occur few hours to days, up to three months after irradiation in acute radiation colitis. It affects rapidly dividing cells of the epithelium and mucosa crypts. This leads to cell death, recruitment and activation of polymorphonuclear (PMN) inflammatory cells, mucosal edema and damage to small blood vessels. The effect of this damage to the mucosa is fluid, electrolyte and nutrient loss. Radiation also reduces bowel motility. Acute radiation colitis is usually transient and self limiting, with regeneration of the epithelium.
  • In chronic radiation colitis, mesenchymal tissue is involved. The damage is progressive with atrophy of the mucosa, fibrosis of the intestinal wall, obliteration of small arteries, chronic ischemia, ulcers, strictures and fistula formation. This changes usually occur three months to years after radiation. Secondary colonic malignancy may occur.

Genetics

There is no specific genetic cause for radiation colitis.

Gross Pathology

Endoscopy should be gentle and with care especially in acute radiation colitis.

• The mucosa may appear erythematous or pale, is edematous, friable with or without small erosions in acute radiation colitis.
• In chronic radiation colitis, mucosa atrophy, fibrosis, obliterative arteritis, stenosis, strictures, fistula and ulcers are seen.

Microscopic Histopathology

Histopathological findings of radiation colitis may be categorized into the following

• Acute: Reduced mitosis, increased apoptosis bodies, mucin depletion, eosinophilia, presence of crypt abscesses and evidence of regeneration
• Chronic: Dilated capillaries and lymphatics, hyaline fibrosis, atypical fibroblast and endothelial cells and distortion of the crypts.

Differentiating radiation colitis from other Diseases

Symptoms of acute radiation proctitis may overlap with other causes of acute colitis, but prior history of radiation will help in distinguishing the cause. Differential diagnosis of acute radiation colitis include:

• Allergic colitis
• Chemical colitis
• NSAID induced colitis
• Ischemic colitis

Differential diagnosis of chronic radiation colitis include:

• Ischemic colitis
• Inflammatory bowel disease

Epidemiology and Demographics

The exact prevalence and incidence of radiation colitis is not certain due to different methods of definition. The incidence of acute radiation injury to the bowel is said to be about 75% to 80% of patients receiving pelvic radiotherapy, while 15% to 20% of patients receiving pelvic radiotherapy will develop chronic radiation injury to the bowel.

Age

The prevalence of radiation colitis is more among older age group (over 60 years) patients. This may be a reflection of the increase frequency of predisposing malignancy requiring radiotherapy in this age group.

Gender

Men and women are affected equally by radiation colitis.

Race

There is no racial predilection to radiation colitis.

Risk Factors

Common risk factors for developing radiation colitis include:

• Radiation dose greater than 54 Gy
• Elderly (above 60 years)
• Past radical abdominal or pelvic surgery such as radical hysterectomy and radical colectomy
• Asthenic individuals
• Smoking
• Chronic co-morbid medical diseases such as diabetes mellitus, hypertension and atherosclerosis
• Past pelvic inflammatory disease
• Collagen vascular disease
• HIV infection- Hypothesized to increase risk for radiation toxicity in the colon

Screening

There are no established screening guidelines for radiation colitis

Natural History, Complications and Prognosis

Natural History

The symptoms and extent of radiation colitis are variable and usually develop insidiously. The symptoms depend on the dose and duration of the radiation and the how sensitive the bowel is to radiation. In acute radiation colitis, symptoms usually starts shortly after commencement of radiation therapy and progress reaching a peak 1 to 2 weeks later. The symptoms of acute radiation colitis may not start for up to 3 months after commencement of radiation. In most cases, the symptoms of acute radiation colitis are self-limiting and resolve following termination of radiation therapy. The symptoms of chronic radiation colitis often become noticeable months to years after the end of radiotherapy. Previous acute radiation colitis does not increase the risk of a patient developing chronic radiation colitis. Treatment is usually required in chronic radiation colitis as resolution of the symptoms is uncommon without intervention.

Complications

Possible complications of radiation colitis include

• Anemia
• Intestinal obstruction
• Intestinal perforation
• Fistula
• Strictures
• Secondary malignancy (rare)