Background The recent availability of open-source Digital Imaging and Communications in Medicine (DICOM) viewer softwares have opened up a new research area for rheumatologists to assess interstitial pulmonary fibrosis (IPF) in systemic sclerosis (SSc).
Objectives First, to evaluate the performance of OsiriX for quantification of disease extent in patients with IPF-SSc and its correlation with physiological impairment, in comparison with reader-based quantification. Secondly, to develop a clinical decision rule to define the extent of IPF.
Methods Seventy-nine patients with SSc, defined on the basis of American Rheumatism Association (ARA) Diagnostic and Therapeutic criteria, were included in the study. All patients showed an IPF at high resolution computed tomography (HRCT) evaluated by two expert radiologists. All HRCT images were reconstructed and analysed by OsiriX software. The interreader agreement for HRCT and Osirix-based scoring have been calculated. Student's t- and the chi-square test were used to compare subgroups of the study population. To determine the relationships with the disease severity, visual reader and OsiriX-based scores were correlated with pulmonary function tests (PFTs) by linear regression analysis and Pearson's correlation. The receiver operating characteristic (ROC) curve was used to explore the discriminant validity of fibrosis ratio.
Results A strong correlation (p<0.0001) between visual reader-based and OsiriX-based results was observed. A close correlation was found between fibrosis ratio and average extent and severity of disease (r =-0.553 and -0.578, respectively) and the average extent of fibrosis and total average HRCT (r =-0.581 and -0.580, respectively). The fibrosis ratio showed a highly significant negative correlation (p<0.0001) with forced vital capacity (FVC) (r=–0.452), forced expiratory volume in 1 s (FEV1) (r=0.504) and the single breath carbon monoxide diffusing capacity of the lung (DLco) (r=0.481) and positive correlation with composite physiologic index (CPI) (r = -0.483). With an optimal cut-off point of 0.88, the fibrosis ratio demonstrated excellent discriminative ability (p=0.0001) to distinguish between patients with limited and extensive lung fibrosis (sensitivity of 85.0%, specificity of 89.7%, positive likelihood ratio of 8.29). The OsiriX-based scoring system was reported to be easier to use and reproducible. The mean time spent completing the quantitative evaluation by OsiriX was 1.3 min and by semiquantitative visual assessment was 10.9 min (p<0.0001).
Conclusions Quantitative indexes measured by OsiriX showed a good correlation with the extent of IFP estimated by visual inspection and PFTs results or HRCT visual scores. Although these data require further validation studies, our results may improve the ability of rheumatologists willing to objectively quantify the extent of IPF in SSc.
Disclosure of Interest None declared