Background Pulmonary function tests (PFT) are recommended and frequently used as a single test for routine screening and early detection of interstitial lung disease (ILD) in systemic sclerosis (SSc). However, more sensitive screening tests might be required for early detection of SSc-ILD and low dose HRCT has been recently developed (1).
Objectives (1) To evaluate the sensitivity of PFTs in comparison to HRCT for the detection of SSc-ILD in routine clinical practice, and (2) To identify predictors of patients with normal PFTs but significant SSc-ILD on HRCT.
Methods Consecutive SSc patients fulfilling ACR criteria were included in our study. Routine assessment was prospectively done according to EUSTAR guidelinesincluding PFT and HRCT in all patients. ILD on HRCT was graded by an experienced, blinded radiologist as follows: mild < 20%, intermediate =20% and severe > 20%. FVC < 80% was considered restrictive lung function. All baseline variables provided from the patients’ database were considered for separating patients with normal FVC and HRCT without fibrosis (PFT-/HRCT-) from patients with normal FVC and HRCT with fibrosis (PFT-/HRCT+). Parameters with p<0.2 in the univariate regression analysis were included in the multivariate analysis.
Results From a total 102 patients available for the analysis, 42 (41%) had diffuse SSc, mean age was 59 years (28-90) and disease duration was 6 years (1-57). There were 27 patients with restrictive pattern on PFT (n=13 FVC 70-80%; n=8 FVC 60-70%; n=6 FVC< 60%) and 64 patients (63 %) had fibrosis on HRCTs (n=45 mild; n=2 intermediate; n=17 severe). Notably, 40/102 (40%) of patients with normal PFTs showed significant ILD on HRCT. Of those, 6 patients (6 %) had severe fibrosis on HRCT with normal PFTs. Vice versa; there were 3 patients (3%) with FVC < 80%, but no significant fibrosis on HRCT. Next, we aimed to define predictors for patients with PFT-/HRCT+. Patients with PFT-/HRCT+ had more frequent anti-Scl-70 antibodies (18/40 vs. 5/35, p < 0.006), less frequent limited SSc (21/40 vs.28 /35, p < 0.02), and less frequent anti-centromere antibodies (ACA) (8/40 vs. 19/35, p < 0.003) in comparison to PFT-/HRCT- . On multivariate analysis, in backward selection, stomach symptoms (OR=0.239, 95% CI=0 .068-0.843, p =0.026), pulmonary artery pressure on echocardiography (OR= 1.062, 95% CI= 1.000 -1.128, p =0.048 ), and ACA (OR=0.250, 95% CI=0.070 -0.892, p =0.033) were identified as independent predictors of lung fibrosis on HRCT in patients with normal FVC, which was confirmed for ACA (OR=0.207, 95% CI=0.072-0.601, p =0.004) in forward selection.
Conclusions PFTs alone have an unacceptable high rate of false negatives in the screening and early detection of SSc-ILD, in particular in patients with diffuse SSc. These data have impact on clinical practice, as they call for the development of more sensitive measures such as low-dose HRCT in the screening for SSc-ILD.
References: Winklehner A, et al, Screening for interstitial lung disease in systemic sclerosis: the diagnostic accuracy of HRCT image series with high increment and reduced number of slices. Ann Rheum Dis,2012;71:549-52.
Disclosure of Interest: Y. Suliman: None Declared, D. Huscher: None Declared, T. D. L. Nguyen-Kim: None Declared, B. Maurer: None Declared, S. Jordan: None Declared, U. Treder: None Declared, R. Speich: None Declared, T. Frauenfelder: None Declared, O. Distler Consultant for: Actelion, Pfizer, Ergonex, BMS, Sanofi-Aventis, United BioSource Corporation, Roche/Genentech, medac, Biovitrium, Boehringer Ingelheim Pharma, Novartis, 4 D Science, Active Biotec and Sinoxa.