Significant differences were found between our patients and controls in FVC, TLC, Deo, and Kco, which considered reflecting changes in lung parenchyma. In contrast, no differences were observed between patients and controls in the indices reflecting small airways obstruction such as MEF25, RY and RV/TLC (Table 2).
Based on MEF25 less than 60 percent of predicted, we found seven (22.6 percent) of 31 patients who had evidence of SAD. This prevalence was no different comparing with the 13 percent of SAD that we found in controls. The above findings suggest that SAD was not common in our studied patients. Moreover, the positive correlation between MEF25 and FEV,/FVC (Fig 1) may suggest that SAD is not an early manifestation in our patients, since large airways obstruction, as mentioned above, is considered a late manifestation of pulmonary involvement in patients with scleroderma. It is also noteworthy that only 2 of 19 patients with pulmonary involvement had SAD as a sole abnormality. This is a further indication that SAD is not an early finding of the disease. The negative correlation that was found between MEF25 and Deo in the patients with abnormal lung function (Fig 2) may suggest that the patients with SAD have less severe lung disease, since supernormal flow rates have been reported to be related to severe fibrotic changes in diffuse interstitial disease.