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Researchers in Zurich studed 102 systemic sclerosis with serial PFTs and high-resolution computed tomography of the chest (HRCT). They found significant interstitial lung disease (ILD) by HRCT in 63 percent. But, only 26 percent had a forced vital capacity (FVC) <80 percent, and 53 percent had a reduction in one or more PFTs.
The false negative rate of FVC was high, with normal FVC in 62.5 percent of patients despite evidence of significant ILD on HRCT. Six percent of patients with normal FVC had severe, functionally-occult lung fibrosis; two of these patients had all PFTs within normal limits.
Compared with ILD-free cases, false negative cases more often had anti-Scl-70 antibodies and diffuse SSc, and less frequently had anti-centromere antibodies (ACAs).
There may be a high risk of missing significant SSc-ILD if relying solely on PFTs. The authors call for more comprehensive screening algorithms for early and accurate detection of ILD.