Diffuse Pulmonary Ossification in Fibrosing Interstitial Lung Diseases: Prevalence and Associations

Purpose To investigate the prevalence of diffuse pulmonary ossification (DPO) in patients with fibrosing interstitial lung disease (ILD) and determine whether there are differences among the types of ILDs. Materials and Methods Institutional review board approval was given and patient consent was not required for this study. The study population comprised 892 consecutive patients with fibrosing ILD, including 456 patients with idiopathic pulmonary fibrosis (IPF) (men, 366; women, 90; median age, 72 years [range, 38-93 years]), 244 with nonspecific interstitial pneumonia (men, 79; women, 165; median age, 60.5 years [range, 23-86 years]), and 192 with chronic hypersensitivity pneumonitis (men, 76; women, 116; median age, 66 years [range, 35-88 years]). Pulmonary ossifications were recorded when nodules (<4 mm diameter) were identified on bone window images (width, 2500 HU; level, 500 HU). DPO was defined as 10 or more bilateral nodular ossifications (definition 1) or as one or more lobes with five or more bilateral nodular ossifications (definition 2). Relationships among pulmonary ossification and parenchymal patterns, clinical parameters, and multidisciplinary team diagnoses were examined. The prevalence of DPO was compared with the χ² statistic or Fisher exact test, and multivariate analysis was performed with logistic regression. Results In the whole population, the prevalence of DPO was 166 (18.6%) and 106 (11.9%) of 892 patients according to definitions 1 and 2, respectively. The prevalence of DPO (definition 1) was significantly higher in patients with IPF (28.5%) than in those without IPF (8.3%, P < .001). Nine of 192 (4.7%) had chronic hypersensitivity pneumonitis (P < .001), and 27 of 244 (11.1%) had nonspecific interstitial pneumonia (P < .001). At multivariate analysis, DPO according to definition 1 was an independent predictor of IPF diagnosis (P < .001) and male sex (P = .003). Coarseness of fibrosing ILD (P = .011) and IPF diagnosis (P = .016) were independently associated with pulmonary ossification profusion. Conclusion DPO is common in patients with fibrosing ILD and is significantly more prevalent in patients with IPF than in those with other fibrosing ILDs, and thus, computed tomographic signs of DPO may be helpful for diagnosis of IPF. ^© RSNA, 2017 Online supplemental material is available for this article.