Ulcerative Colitis and Diffuse Interstitial Lung Disease: Rare Association or Complete Coincidence?-Reply

In Reply.—  Ulcerative colitis has an estimated prevalence of 70 to 150 per 100 000.^1,2 If one assumes a similar prevalence for idiopathic pulmonary fibrosis, the probability that both diseases independently will occur by chance in the same patient is roughly one per million. Such an infrequent association of the two diseases contradicts the approximately 25% to 50% prevalence of physiological pulmonary disease and the 4% to 6% prevalence of radiographic interstitial lung disease in reported series of patients with inflammatory bowel disease.^3,4Several chronic inflammatory disorders of unknown etiology have commonly associated interstitial pulmonary disease: specifically, rheumatoid arthritis, progressive systemic sclerosis, and polymyositis/dermatomyositis. The interstitial lung disease in these disorders is indistinguishable from idiopathic pulmonary fibrosis and is attributable to the specific collagen-vascular disease purely on clinical grounds. In fact, the associated frequency of interstitial lung disease in rheumatoid arthritis or systemic sclerosis (25% to 50%) approximates