Association of collagenous colitis with prurigo nodularis

The etiology and pathogenesis of collagenous colitis (CC) is poorly understood and probably multifactorial; many potential pathophysiological mechanisms have been described, although none have been conclusively proved. Circumstantial evidence suggests that CC appears as an autoimmune response to a luminal or epithelial antigen of unknown origin. Infections and certain drugs (e.g. NSAID, lansoprazole) may act as triggers for an immune-mediated process. CC is characterized clinically by chronic watery, nonbloody diarrhea with normal endoscopic appearance and without radiological abnormalities, but specific microscopic changes in the colon. Histopathology is featured by the presence of a thickened subepithelial collagen band adjacent to the basal membrane. Up to 40% of patients with CC have associated diseases of autoimmune or inflammatory origin, such as thyroid disease, coeliac disease, rheumatoid arthritis, diabetes mellitus, Sjögren's syndrome, CREST syndrome, scleroderma, pernicious anemia, and sarcoidosis. Prurigo nodularis is a chronic condition characterized by intensely pruritic, lichenified, or excoriated papules and nodules of unknown etiology. It is assumed to represent a cutaneous reaction pattern to repeated scrubbing or scratching caused by pruritus. We report a case of CC and prurigo nodularis. To our knowledge, this association has not been reported earlier.