Microscopic colitis is an inflammatory disease of the colon and a frequent cause of chronic or recurrent watery diarrhea, particularly in older persons. MC consists of two subtypes, collagenous colitis (CC) and lymphocytic colitis (LC). While the primary symptom is diarrhea, other signs and symptoms such as abdominal pain, weight loss, and dehydration or electrolyte abnormalities may also be present depending on disease severity.1 In MC, the colonic mucosa usually appears normal on colonoscopy, and the diagnosis is made by histologic findings of intraepithelial lymphocytosis with (CC) or without (LC) a prominent subepithelial collagen band. The management approaches to CC and LC are similar and should be directed based on the severity of symptoms.2 We review the epidemiology, risk factors, pathophysiology, diagnosis, and clinical management for this condition, as well as novel therapeutic approaches.
Although the incidence of MC increased in the late twentieth century, more recently, it has stabilized with an estimated incidence varying from 1 to 25 per 100,000 person-years.3-5 A recent meta-analysis revealed a pooled incidence of 4.85 per 100,000 persons for LC and 4.14 per 100,000 persons for CC.6 Proposed explanations for the rising incidence in the late twentieth century include improved clinical awareness of the disease, possible increased use of drugs associated with MC, and increased performance of diagnostic colonoscopies for chronic diarrhea. Since MC is now well-recognized, the recent plateau in incidence rates may reflect decreased detection bias.
The prevalence of MC ranges from 10%-20% in patients undergoing colonoscopy for chronic watery diarrhea.6,7 The prevalence of LC is approximately 63.1 cases per 100,000 person-years and, for CC, is 49.2 cases per 100,000 person-years.6-8 Recent studies have demonstrated increasing prevalence of MC likely resulting from an aging population.9,10
Female gender, increasing age, concomitant autoimmune disease, and the use of certain drugs, including NSAIDs, proton pump inhibitors (PPIs), statins, and selective serotonin reuptake inhibitors (SSRIs), have been associated with an increased risk of MC.11,12 Autoimmune disorders, including celiac disease (CD), rheumatoid arthritis, hypothyroidism, and hyperthyroidism, are more common in patients with MC. The association with CD, in particular, is clinically important, as CD is associated with a 50-70 times greater risk of MC, and 2%-9% of patients with MC have CD.13,14
Several medications have been associated with MC. In a British multicenter prospective study, MC was associated with the use of NSAIDs, PPIs, and SSRIs;15 however, recent studies have questioned the association of MC with some of these medications, which might worsen diarrhea but not actually cause MC.16
An additional risk factor for MC is smoking. A recent meta-analysis demonstrated that current and former smokers had an increased risk of MC (odds ratio, 2.99; 95% confidence interval, 2.15-4.15 and OR, 1.63; 95% CI, 1.37-1.94, respectively), compared with nonsmokers.17 Smokers develop MC at a younger age, and smoking is associated with increased disease severity and decreased likelihood of attaining remission.18,19