A 68-year-old woman has a 10-month history of non-bloody diarrhea with abdominal pain. She has lost 4.5kg (10 lb). She occasionally passes mucus per rectum but does not have steatorrhea. She has not had any travel or new medications. She has no medical history, and physical examination and laboratories, including stool studies, are normal. She has been diagnosed with irritable bowel syndrome, but has not responded to antidiarrheals or antispasmodics. She is referred for a second opinion.
Trials of loperamide and bismuth subsalicylate were unhelpful. She was started on budesonide, 9mg/day, with resolution of her diarrhea.
The use of non-steroidal anti-inflammatory drugs or other medications that might be associated with microscopic colitis should be discontinued if possible. In addition, any other agent (e.g., dairy products) that may cause diarrhea should be avoided. Antidiarrheal therapy, such as loperamide or diphenox-ylate, can be effective in mild case. If these agents are unsuccessful, bismuth subsalicylate may be beneficial.
If diarrhea does not respond to bismuth, the next therapeutic intervention considered often is mesalamine. However, large series have reported benefit in fewer than half of the patients treated with these drugs. Cholestyramine may be more effective.
Patients refractory to these medications may respond to corticosteroids, which are the best therapies reported in the largest series (Table Response to therapy in microscopic colitis). Budesonide has been effective in controlled studies in collagenous and lymphocytic colitis, as well as in clinical experience.
Table Response to therapy in microscopic colitis
|Study [reference] Type of colitis Number of subjects||PardiLymphocytic
|Bohr Collage nous 163|
Because of this efficacy, some physicians prescribe budesonide as first-line therapy in microscopic colitis. However, relapse after discontinuation is common, and many patients become steroid dependent. Thus, before starting corticosteroids, alternative diagnoses such as celiac disease, should be excluded. For steroid-refractory or dependent patients, immune modifiers such as azathioprine can be considered. Alternatively, some clinicians use low-dose (3-6mg/day) budesonide chronically.
Other treatments have been reported, but with limited experience. Rarely, surgery is necessary. The response rates to various medications from three large uncontrolled series are listed in Table Response to therapy in microscopic colitis.
Most patients will respond to the treatment algorithm suggested above but it is not clear how long to continue therapy, since many patients will have spontaneous or treatment-induced remissions and may not require long-term therapy. Treatment should be continued for 8-12 weeks, followed by tapering. For recurrent symptoms, maintenance therapy or episodic retreatment is used.
Many patients have a waxing and waning course. Self-limited single attacks and spontaneous resolution have been reported. The rate of spontaneous or treatment-induced complete remission with prolonged follow up ranges from 59 to 93% in lymphocytic colitis and from 2 to 92% in collagenous colitis. Of those without full remission, some have intermittent symptoms and do not require maintenance therapy, but many (especially those requiring steroids) will. There is no evidence of an increased risk of colon cancer or mortality.
• Microscopic colitis is a common cause of chronic watery diarrhea.
• It is more common in the elderly, and in females.
• Symptoms are similar to irritable bowel syndrome; biopsies are required to distinguish these diagnoses.
• Some cases are associated with common medications.
• Celiac disease is more common in microscopic colitis.
• Bismuth subsalicylate appears to be an effective therapy.
• Budesonide is very effective, but recurrence is common after discontinuation.
Microscopic colitis is a common cause of chronic watery diarrhea, especially in the elderly. The incidence of this condition is increasing, perhaps due to an association with several commonly used medications. The two subtypes, lymphocytic and collagenous colitis, are only distinguishable histologically. The diagnosis relies on colon biopsies, which show an intraepithelial lymphocytosis and mixed lamina propria inflammation. In collagenous colitis, the subepithelial collagen band is thickened. The main differential diagnosis is irritable bowel syndrome, and histology is required to distinguish these entities. Several treatment options have been reported, but bismuth subsalicylate and budesonide seem to be the most effective. Many patients require maintenance therapy, but the prognosis is good, with most patients responding to treatment, and no known increased risk of colon cancer or death.