Microscopic colitis: A common, yet often overlooked, cause of chronic diarrhea

The diagnosis of MC is made by biopsy of the colonic mucosa demonstrating characteristic pathologic features.³² Unlike in diseases such as Crohn’s disease or ulcerative colitis, the colon usually appears normal in MC, although mild nonspecific changes, such as erythema or edema, may be visualized. There is no consensus on the ideal location to obtain biopsies for MC or whether biopsies from both the left and the right colon are required.^2,33 The procedure of choice for the diagnosis of MC is colonoscopy with random biopsies taken throughout the colon. More limited evaluation by flexible sigmoidoscopy with biopsies may miss cases of MC as inflammation and collagen thickening are not necessarily uniform throughout the colon; however, in a patient that has undergone a recent colonoscopy for colon cancer screening without colon biopsies, a flexible sigmoidoscopy may be a reasonable next test for evaluation of MC, provided biopsies are obtained above the rectosigmoid colon.³⁴

^{Courtesy Dr. Catherine Hagen/Mayo Clinic}

Figure 1A. Histopathology of lymphocytic colitis.

The MC subtypes are differentiated based on histology. The hallmark of LC is less than 20 intraepithelial lymphocytes per 100 surface epithelial cells (normal, less than 5) (Figure 1A). CC is characterized by a thickened subepithelial collagen band greater than 7-10 micrometers (normal, less than 5) (Figure 1B). For a subgroup of patients with milder abnormalities that do not meet these histological criteria, the terms “microscopic colitis, not otherwise specified” or “microscopic colitis, incomplete” may be used.³⁵ These patients often respond to standard treatments for MC. There is an additional subset of patients with biopsy demonstrating features of both CC and LC simultaneously, as well as patients transitioning from one MC subtype to another over time.^32,35

^{Courtesy Dr. Catherine Hagen/Mayo Clinic}

Figure 1B. Histopathology of collagenous colitis.

Management approach

The first step in management of patients with MC includes stopping culprit medications if there is a temporal relationship between the initiation of the medication and the onset of diarrhea, as well as encouraging smoking cessation. These steps alone, however, are unlikely to achieve clinical remission in most patients. A stepwise pharmacological approach is used in the management of MC based on disease severity (Figure 2). For patients with mild symptoms, antidiarrheal medications, such as loperamide, may be helpful.³⁶ Long-term use of loperamide at therapeutic doses no greater than 16 mg daily appears to be safe if required to maintain symptom response. For those with persistent symptoms despite antidiarrheal medications, bismuth subsalicylate at three 262 mg tablets three times daily for 6-8 weeks can be considered. Long-term use of bismuth subsalicylate is not advised, especially at this dose, because of possible neurotoxicity.³⁷

For patients refractory to the above treatments or those with moderate-to-severe symptoms, an 8-week course of budesonide at 9 mg daily is the first-line treatment.³⁸ The dose was tapered before discontinuation in some studies but not in others. Both strategies appear effective. A recent meta-analysis of nine randomized trials demonstrated pooled ORs of 7.34 (95% CI, 4.08-13.19) and 8.35 (95% CI, 4.14-16.85) for response to budesonide induction and maintenance, respectively.³⁹

Cholestyramine is another medication considered in the management of MC and warrants further investigation. To date, no randomized clinical trials have been conducted to evaluate bile acid sequestrants in MC, but they should be considered before placing patients on immunosuppressive medications. Some providers use mesalamine in this setting, although mesalamine is inferior to budesonide in the induction of clinical remission in MC.⁴⁰

Despite high rates of response to budesonide, relapse after discontinuation is frequent (60%-80%), and time to relapse is variable^41,42 The American Gastroenterological Association recommends budesonide for maintenance of remission in patients with recurrence following discontinuation of induction therapy. The lowest effective dose that maintains resolution of symptoms should be prescribed, ideally at 6 mg daily or lower.³⁸ Although budesonide has a greater first-pass metabolism, compared with other glucocorticoids, patients should be monitored for possible side effects including hypertension, diabetes, and osteoporosis, as well as ophthalmologic disease, including cataracts and glaucoma.

For those who are intolerant to budesonide or have refractory symptoms, concomitant disorders such as CD that may be contributing to symptoms must be excluded. Immunosuppressive medications – such as thiopurines and biologic agents, including tumor necrosis factor–alpha inhibitors or vedolizumab – may be considered in refractory cases.^43,44 Of note, there are limited studies evaluating the use of these medications for MC. Lastly, surgeries including ileostomy with or without colectomy have been performed in the most severe cases for resistant disease that has failed numerous pharmacological therapies.⁴⁵

Patients should be counseled that, while symptoms from MC can be quite bothersome and disabling, there appears to be a normal life expectancy and no association between MC and colon cancer, unlike with other inflammatory conditions of the colon such as IBD.^46,47