Epidemiologic survey of Japanese patients with idiopathic pulmonary fibrosis and investigation of ethnic differences

Rationale: Idiopathic pulmonary fibrosis (IPF) has an unknown etiology and poor prognosis. Several large-scale epidemiologic studies have been conducted predominantly in Western countries. There are few studies reported from Asian countries. It remains unclear whether ethnic difference exists in IPF. It is important to determine the current IPF status in Asian populations and compare it with that of Western populations.

Objectives: To provide the epidemiologic status of IPF in Japan and to investigate ethnic differences.

Methods: We selected Hokkaido prefecture (population, 5.6 million) as the epidemiologic cohort of IPF among Japanese. On the basis of the clinical records of 553 patients with IPF who were accepted based on the application of the Certificate of Medical Benefit between 2003 and 2007, we conducted a retrospective epidemiologic and prognostic analysis.

Measurements and main results: The prevalence and cumulative incidence of IPF was 10.0 and 2.23 per 100,000 population, respectively, with 72.7% predominance of males and an increase in frequency with age. The median survival time was 35 months, and the most common (40%) cause of death was acute exacerbation. The most important factor influencing IPF prognosis was the percent vital capacity.

Conclusions: The status of IPF in the Japanese population was clarified for the first time through our study. Our results showed that in men, the incidence of death caused by acute exacerbation was higher and that caused by cardiovascular disease was lower in Japan than in Western countries. These results may suggest ethnic differences in IPF.