Collagenous colitis is an inflammatory condition of the colon. Together with the related condition lymphocytic colitis, it is a subtype of microscopic colitis, which is characterized by inflammation that specifically affects the colon (i.e. colitis), and a clinical presentation that involves watery diarrhea but a lack of rectal bleeding. Microscopic colitis does not usually cause macroscopic changes to the colon that allow a visual diagnosis during colonoscopy, instead causing microscopic changes that can be detected through histopathological examination of colonic biopsies. The nature of these microscopic changes is what differentiates collagenous from lymphocytic colitis, with the characteristic finding in collagenous colitis being depositions of collagen in the connective tissue between the colonic glands. Collagenous colitis, and microscopic colitis as a whole, is sometimes considered to be an inflammatory bowel disease (IBD) along with Crohn's disease and ulcerative colitis. However, little is known about the etiology of microscopic colitis, and so the degree of similarity to the inflammatory bowel diseases is uncertain.
Although cases are known to occur in all age groups, the disease is most frequently diagnosed in late middle aged or elderly people, with the average person being diagnosed in their 60s. Women are more frequently affected than men, with different studies finding female-male incidence ratios of between 3 and 8. Epidemiological studies have found large increases in diagnosed cases of microscopic colitis, of which collagenous colitis cases are a majority, over the past few decades, with cases of microscopic colitis now outnumbering those of Crohn's disease and ulcerative colitis at least in some regions.
Signs and symptoms
In general, microscopic colitis causes chronic watery diarrhea with increased stool frequency. Some patients report nocturnal diarrhea, abdominal pain, bowel urgency, fecal incontinence, fatigue and weight loss. In severe cases, symptoms may include dehydration and electrolyte imbalances. Patients report a significantly diminished quality of life. In a retrospective study specifically on collagenous colitis patients, all studied patients experienced chronic diarrhea, 42% experienced weight loss, 41% experienced abdominal pain, 27% of the patients experienced nocturnal diarrhea, while 14% experienced fatigue and 8% experienced meteorism. The median patent had 6 stools per day. Among the patients who experienced weight loss and whose magnitude of weight loss was recorded, the median lost weight was 6 kg.
Causes
The cause of collagenous colitis is unknown. A connection with autoimmune disorders such as celiac disease is suspected, as up to 40% of patients with collagenous colitis have an autoimmune disease. Use of nonsteroidal anti-inflammatory drugs (NSAIDs), proton pump inhibitors (PPIs) and beta blockers also appear to increase the risk of collagenous colitis, but the cause of this is not known.
Diagnosis
On colonoscopy, the mucosa of the colon typically looks normal, but biopsies of affected tissue usually show deposition of collagen in the lamina propria, which is the area of connective tissue between colonic glands. Radiological tests, such as a barium enema are also typically normal.
Treatment
First line treatment for collagenous colitis is the use of budesonide, a steroid that works locally in the colon and is highly cleared by first pass effect. Other medications that can be used include the following:
Bismuth agents, including Pepto-Bismol
5-aminosalicylic acid
Immunosuppressants, including azathioprine
Infliximab
Pilot-scale studies have shown some evidence of possible benefit for both Boswellia serrata extract and specific strains of probiotics in the treatment of collagenous colitis, although larger sample sizes are needed to confirm the results.