Microscopic Colitis: A Challenging Disorder.

BACKGROUND: The clinical importance of microscopic colitis (MC) is increasing. This is explained by both the increasing incidence and the challenges posed by the disease. However, recent MC data also reveal a number of doubts and uncertainties. SUMMARY: This review focuses on current knowledge of MC and highlights the various controversies and criticisms regarding the clinical data about definitions, subtypes, pathogenesis, diagnosis, and treatment of this condition. Key Messages: The diagnosis of MC is based on histology, which distinguishes 2 subtypes. However, transitional forms often cause misclassification, which calls into question the reality (specificity, meaning) of the distinction between the 2 forms. The location of the colon biopsy is not defined by international consensus. There is no credible, clear explanation for the incidence increase. The pathogenesis is unknown, probably multifactorial, but the importance of the immunological background is increasing. The natural history of the disease and the underlying cause of relapses are unclear. It is suggested that MC would be the prelude of IBD. Further data collection is needed to clarify these issues.