FIBROSING ALVEOLITIS IN SYSTEMIC-SCLEROSIS - INDEXES OF LUNG-FUNCTIONIN RELATION TO EXTENT OF DISEASE ON COMPUTED-TOMOGRAPHY

Objective. Thin-section computed tomography (CT) provides a sensitive and reproducible method of quantifying the morphologic extent of disea se in the clinical management of fibrosing alveolitis associated with systemic sclerosis (FASSc). The aim of this study was to determine whi ch indices of lung function best reflect the extent of disease on CT i n FASSc, and to determine the independent influences of smoking histor y, extent of fibrosing alveolitis, demographic features, and concurren t treatment upon functional impairment in FASSc. Methods. Sixty-four p atients with FASSc were studied using CT and static and exercise lung function testing. Statistical relationships were determined by multipl e regression analyses. Results. Five patients with overt pulmonary hyp ertension were characterized by severe impairment in 3 indices of lung function: diffusing capacity for carbon monoxide (DLCO), DLCO adjuste d for alveolar volume (KCO), and arterial partial pressure of oxygen. On multiple regression analysis, the major determinant of functional i mpairment was the extent of fibrosing alveolitis on CT. A history of s moking was independently associated with preservation of total lung ca pacity and depression of KCO, but did not othenvise influence function al-morphologic correlations. The percent predicted DLCO correlated bet ter with extent of disease on CT (r = -0.70) than did oxygen desaturat ion on (r = 0.55), the physiologic component of the clinical-radiograp hic-physiologic score (CRP index) (r = 0.52), or other indices of lung function. Lung volume measures correlated poorly with disease extent on CT. Conclusion. The percent predicted DLCO best reflects the extent of fibrosing alveolitis in FASSc, and therefore should be measured in routine evaluations. Exercise testing may also have a useful role in staging the severity of pulmonary fibrosis, but the CRP index offers n o additional advantage over the DLCO and exercise testing.