Purpose: (1) To evaluate the relationship between the degree of pulmonary involvement by systemic sclerosis (SSc) and the degree of involvement of other organ systems by SSc at baseline. (2) To assess the degree of impairment in lung function at presentation and the annual rate of change in lung function to predict the rate of progression of involvement of extrapulmonary organ systems by SSc over time. (3) To determine whether survival in patients with SSc can be predicted from the degree of lung function impairment at baseline or from the annual rate of change in lung function.
Methods: Semiquantitative indices of pulmonary and extrapulmonary involvement and pulmonary function tests (PFTs) were analyzed and compared in 62 nonsmoking scleroderma patients enrolled in a 3-year prospective drug trial, vs 47 in a "study group" who underwent serial evaluation. The other 16 "early withdrawals" withdrew prior to the second evaluation. The indices of organ system involvement were based on clinical, physiologic, and biochemical findings as previously published. The PFTs included total lung capacity (TLC), forced vital capacity (FVC), FEV1, and single-breath diffusing capacity for carbon monoxide (Dsb). Annualized rates of change in PFTs and indices of extrapulmonary involvement were calculated for each subject from data collected on at least 2 separate occasions at least 6 months apart. Spearman rank correlations were performed between individual baseline PFTs (expressed as percent predicted) and (a) indices of extrapulmonary involvement at baseline, (b) annualized rates of change in PFTs, and (c) annualized rates of change in indices of extrapulmonary involvement. Correlations also were performed between the rate of change in each lung function measure and rates of change in indices of extrapulmonary involvement. The ability of PFTs at baseline and their rates of change to predict cumulative survival was assessed by Cox stepwise regression.
Results: The degree of impairment in baseline PFTs was related to involvement of the right side of the heart but not to other extrapulmonary system involvement. Baseline PFTs were not related to the rate of subsequent decline of lung function or worsening of extrapulmonary organ system involvement. Subsequent annual rates of decline in lung function were related to worsening skin and upper gastrointestinal involvement. Cumulative survival may be related to the rate of decline in DCO, TLC, and FVC, but was not predicted by impairment in any measure of lung function.
Conclusion: With the exception of involvement of the right side of the heart consistent with cor pulmonale, the degree of pulmonary involvement by SSc was not correlated with the extent of extrapulmonary involvement. The degree of pulmonary involvement by SSc did not predict subsequent worsening of either pulmonary or extrapulmonary involvement. Worsening pulmonary involvement by SSc, in general, does not correlate with worsening involvement of extrapulmonary organ systems, except for the skin and upper gastrointestinal tract. A rapid decline in DCO or lung volumes may predict poor survival.