Interstitial lung disease (ILD) is the leading cause of death in patients with systemic sclerosis (SSc). Although pulmonary function tests (PFTs) are commonly used to screen for ILD in patients with SSc, studies have shown that they lack sensitivity for the detection of ILD in general SSc cohorts. This study was undertaken to assess the performance characteristics of PFTs for the detection of ILD in patients with early diffuse cutaneous SSc (dcSSc), a population at high risk for the development of ILD.
We performed a retrospective cohort study of patients enrolled in the Prospective Registry of Early Systemic Sclerosis at 11 sites in the US between April 2012 and January 2019. Patients were included if they underwent spirometry and high-resolution computed tomography (HRCT) of the chest. We calculated the performance characteristics of PFTs for the detection of ILD on HRCT.
The study included 212 patients, 54% of whom had radiographic ILD. For the detection of ILD on HRCT imaging, a forced vital capacity (FVC) <80% predicted had a sensitivity of 63%. The combination of FVC <80% predicted or diffusing capacity for carbon monoxide (DLco) <80% predicted improved the sensitivity to 85%. An FVC <80% predicted had a negative predictive value (NPV) of 61%, while the combination of FVC <80% predicted or DLco <80% predicted had an NPV of 70%.
PFTs alone are an inadequate screening tool for the diagnosis of ILD in patients with early dcSSc. HRCT should be part of the ILD screening algorithm in patients with dcSSc.