[Present status of idiopathic interstitial pneumonia--from epidemiology to etiology]

The present status of idiopathic interstitial pneumonia (IIP) was evaluated from data collected as part of the Financial Support Program for patients with IIP, conducted in Hokkaido since 1979. The prevalence of IIP in 1992 was 4.08/100,000, and the yearly incidence was 1.23/100,000. The ratio of men to women was 1.85/1.0. Under age 55, women were more numerous than men, and over age 55, men were more numerous than women. Clinical and epidemiological analyses of the patients with IIP, with collagen vascular disease-interstitial pneumonia suggested possible contribution of dust inhalation to the etiology IIP. A prospective study revealed that about 20% of the subjects had systemic signs and symptoms of collagen diseases from 2 months to 10 years after the diagnosis of IIP. In addition, about 15% of the subjects with IIP developed lung cancer during the follow-up period. This incidence was significantly higher than that in the patients with chronic obstructive pulmonary diseases and the same smoking history, which suggests that IIP itself is a risk factor for lung cancer.