BackgroundThe FinnishIPF registry is a prospective, longitudinal national registry study on the epidemiology of idiopathic pulmonary fibrosis (IPF). It was designed to describe the characteristics, management and prognosis of prevalent and incident IPF patients. The study was initiated in 2012.MethodsWe present here results limited to five university hospitals. Patients with IPF were screened from hospital registries using ICD-10 diagnosis codes J84.1 and J84.9. All patients who gave informed consent were included and evaluated using novel diagnostic criteria. Point prevalence on the 31st of December in 2012 was calculated using the reported population in each university hospital city as the denominator.ResultsPatients with ICD-10 codes J84.1 and J84.9 yielded a heterogeneous group – on the basis of patient records assessed by pulmonologists only 20–30 % of the cases were IPF. After clinical, radiological and histological re-evaluation 111 of 123 (90 %) of patients fulfilled the clinical criteria of IPF. The estimated prevalence of IPF was 8.6 cases/100 000. 60.4 % were men. Forty four percent of the patients were never-smokers. At diagnosis, the patients’ mean age was 73.5 years and mean FVC was 80.4 % and DLCO 57.3 % of predicted.ConclusionsOur results suggest that hospital registries are inaccurate for epidemiological studies unless patients are carefully re-evaluated. IPF is diagnosed in Finland at a stage when lung function is still quite well preserved. Smoking in patients with IPF was less common than in previous reports.

The histologic manifestation of idiopathic pulmonary fibrosis (IPF) is usual interstitial pneumonia (UIP), which is a good prognostic determinant of survival compared with other histologic interstitial lung disease patterns. According to the current international guidelines, the histologic features of suspected IPF/UIP are divided into 4 categories: UIP, probable UIP, possible UIP, and not UIP pattern. Four pulmonary pathologists who were blinded to clinicoradiologic information reevaluated 50 surgical lung biopsies (83.3%), 6 lung explant (10.0%), and 4 autopsy samples (6.7%) from the FinnishIPF registry (N=60) using the current diagnostic guidelines. Additional histologic features atypical for UIP were also evaluated and compared with clinicora-diologic information. The interobserver agreement of pathologists was examined by Cohen kappa (κ) coefficient; the survival of the patients was estimated with Kaplan-Meier curves. The histologic reevaluation indicated that 38 of 60 patients (63.3%) had definite UIP. Inflammation was the most common additional histologic finding (15/60, 25.0%). The interobserver agreement on histologic diagnosis ranged from slight (κ=0.044) to substantial (κ=0.779). The interobserver agreement varied extensively with regard to the presence of giant cells. The observed histologic features displayed no association with radiologic patterns or survival. Definite UIP and honeycombing findings in high-resolution computed tomography correlated with poor prognosis. A high level of interobserver variability was observed between pathologists, even in this well-defined cohort of IPF patients, which highlights the importance of multidisciplinary decision making in IPF diagnostics and stresses the need for a reassessment of the histologic criteria.