Association of common variable immunodeficiency with atypical collagenous colitis.

Collagenous colitis is a condition characterized by chronic, watery diarrhoea, which is diagnosed histologically as most cases reveal a normal colonoscopic appearance. The aetiology is poorly understood, but nonsteroidal anti-inflammatory drugs or infections may act as triggers for an immune-mediated process. In this report, an unusual case of collagenous colitis associated with pseudomembrane formation is described. Stool assay was negative for Clostridium difficile cytotoxin B. There are only three reports of pseudomembranes in collagenous colitis in the absence of C. difficile infection. In addition, the patient had a deficiency in immunoglobulin production, which may suggest an infective trigger to collagenous colitis. This is the first report of an association between an immunoglobulin deficiency and this unusual variant of collagenous colitis. The implications of these findings are discussed.