Disease progression in idiopathic pulmonary fibrosis without pulmonary function impairment

Background and objective Despite significant recent progress in the understanding of idiopathic pulmonary fibrosis (IPF), the early phase of the disease is still poorly understood. We studied patients with IPF without pulmonary function impairment in order to determine the clinical features, natural history and key findings for physiological progression. Methods Twenty-five patients without pulmonary function impairment were identified from among patients with previously diagnosed IPF who underwent surgical lung biopsies between January 1997 and December 2006 at our institutions. 'Without pulmonary function impairment' was defined as both forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLco) >80% predicted. Patients diagnosed with IPF through multidisciplinary discussion based on the new IPF guidelines were the subjects of this study. Results Sixteen patients had a confirmed diagnosis of IPF. Eleven patients presented with chest X-ray abnormality found during an annual health examination. Seven patients were asymptomatic. Eleven patients showed physiological disease progression (median time; 19.9 ± 12.3 months) defined by a decline of at least 10% in FVC or at least 15% in DLco. Univariate analysis revealed that both usual interstitial pneumonia pattern and extent of honeycombing on high-resolution computed tomography (HRCT) were factors associated with disease progression (odds ratio 5.634, 95% confidence interval 1.364-23.278; odds ratio 2.371/5%, 95% confidence interval 1.042-5.395). Conclusions IPF patients without pulmonary function impairment have a progressive but slow clinical course. The existence and extent of honeycombing on HRCT are predictive of disease progression. Patients with IPF without pulmonary function impairment have a progressive clinical course with slow decline in pulmonary function, which is compatible with the early phase of IPF. Physiological disease progression at an early stage of IPF may be influenced by the existence and extent of honeycombing on HRCT.