Collagenous, microscopic and lymphocytic colitis. An evolving concept.

Collagenous colitis and lymphocytic colitis (previously described as microscopic colitis) are two newly recognised forms of colitis. Both have generated much controversy and continue to do so; their aetiology and pathogenesis are unresolved and their association with a variety of immune-related disorders is intriguing. Response to available therapeutic modalities is often disappointing. The possible relationship or overlap between these two conditions remains a controversial issue. The aim of this review is essentially to present an overview of collagenous colitis and lymphocytic colitis and to propose an unifying concept with an adapted terminology.