Background/Purpose: Forced vital capacity (FVC) and carbon monoxide diffusion (DLCO) are used to screen for systemic sclerosis associated interstitial lung disease (SSc-ILD). The purpose of this cross-sectional study was to determine the sensitivity, specificity, and negative predictive values (NPV) of FVC and DLCO thresholds for SSc-ILD on chest high-resolution computed tomography (HRCT) scans.

Methods: Patients fulfilled American College of Rheumatology 2013 SSc criteria and had undergone at least one HRCT and pulmonary function test (PFT). An experienced thoracic radiologist quantified ILD on HRCT. Receiver operating characteristic curves were generated to determine optimal % predicted FVC and DLCO cut-points, defined as the greatest combined sensitivity and specificity, for radiographic ILD. Established ÒnormalÓ PFT thresholds and screening algorithms combining FVC and DLCO were evaluated. Sub-analysis was performed according to anti-topoisomerase I (Scl-70) autoantibody status.

Results: A total of 265 patients fulfilled study criteria (82% women, 49% diffuse cutaneous SSc, 30% +Scl-70), and 188 (71%) had radiographic ILD. Of those with ILD, 59 out of 188 (31%) had ÒnormalÓ FVC (>80% predicted), and 65 out of 151 (43%) had ÒnormalÓ DLCO (>60% predicted). There were 31 out of 214 (14%) patients who had FVC and DLCO both within ÒnormalÓ range. Predicted FVC <=80% (sensitivity 0.69, specificity 0.74), and DLCO <=62% (sensitivity 0.60, specificity 0.70) were the optimal thresholds for ILD (Table 1, Figure 1). All evaluated FVC and DLCO threshold combinations had a NPV <0.70 for radiographic ILD. In patients with positive vs. negative Scl-70, the NPV of % predicted FVC <80 (0.05 vs. 0.57) and DLCO <60 (0.10 vs. 0.48) was lower for radiographic ILD (Table 1).

Conclusion: Radiographic ILD is prevalent in SSc patients despite normal PFTs. No observed % predicted FVC or DLCO threshold combinations yielded a high NPV for SSc-ILD screening. A % predicted FVC >=80 and DLCO >=60 in SSc patients, especially those with positive vs. negative Scl-70 autoantibodies, should not obviate consideration of HRCT for ILD evaluation. However, it remains to be shown if detection of ILD in asymptomatic patients with normal PFTs improves clinical outcomes.