The American Journal of Gastroenterology
Microscopic colitis: epidemiology and treatment
Introduction
The term microscopic colitis describes a syndrome of chronic, watery diarrhea, normal or near-normal endoscopic appearance of colonic mucosa, and histopathologic abnormalities. Microscopic colitis can be classified as either lymphocytic or collagenous. Both subtypes are characterized by colonic intraepithelial lymphocytosis and expansion of the lamina propria with chronic and, to a lesser extent, acute inflammatory cells; collagenous colitis is distinguished by the presence of a thickened subepithelial collagen band. These conditions were first described only 2 to 3 decades ago 1, 2, 3, and there has been exponential growth in the recognition and understanding of these idiopathic conditions. Microscopic colitis and its subtypes have been reviewed extensively recently 4, 5, 6, but our knowledge of the epidemiology of these conditions has continued to evolve. Moreover, therapy for microscopic colitis has seen considerable advances in the past 2 yr. This review will focus on the epidemiology and treatment of lymphocytic and collagenous colitis.
Section snippets
Epidemiology and pathogenesis
The incidence and prevalence of microscopic colitis have been difficult to estimate. First, most reports of collagenous and lymphocytic colitis have been case reports or case series from referral centers, and in these studies no suitable denominator to determine an incidence rate or a prevalence has been available. Studies from a defined region with a known population are most suitable for determining the true incidence and prevalence of a condition. Second, the diagnostic awareness of these
Clinical features and natural history
The clinical features of microscopic colitis have been reviewed elsewhere (6). In brief, patients present with either the gradual or sudden onset of watery diarrhea, sometimes associated with abdominal cramping and weight loss. The prevalence of autoimmune conditions, such as rheumatoid arthritis and thyroid disease, seems to be higher than expected in microscopic colitis, and some patients will be found to have elevated erythrocyte sedimentation rates or the presence of antinuclear antibodies.
Treatment
The treatment of microscopic colitis is beginning to move from the empiric to the evidence-based realm. Until recently, most reports of therapy had been uncontrolled observations. Treatments described in these studies have ranged from antidiarrheals and aminosalicylates to immunosuppressive agents and even surgery. The two largest case series of collagenous (32) and lymphocytic colitis (23) are worth examining in more detail. In an observational study of 163 collagenous colitis patients from
Conclusion
Understanding of the epidemiology and treatment of microscopic colitis continues to expand. These idiopathic conditions present with chronic, watery diarrhea, most often in middle-aged or elderly women, and they seem to be increasing in frequency. Treatment is beginning to move in an evidence-based direction with the availability of randomized, clinical trials, especially for the treatment of collagenous colitis. There is a need for treatment trials in lymphocytic colitis and for maintenance
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