Static lung compliance as an index of early pulmonary disease in systemic sclerosis

Pulmonary function abnormalities constitute the most important cause of morbidity and mortality in patients with systemic sclerosis (SSc). A restrictive ventilatory defect with a reduction in pulmonary carbon monoxide diffusion capacity (DLCO) is the commonest finding. Static lung compliance (Cst) is perhaps the most sensitive parameter for the detection of abnormal pulmonary mechanics. We compared the results of Cst and DLCO in patients with SSc and normal spirometry to identify early pulmonary disease. Sixteen of 50 patients had normal spirometry, eight of whom had abnormal Cst. Four of them also had a reduced DLCO. Two patients had abnormal DLCO but their Cst was normal. One of them had pulmonary hypertension on echocardiography. We conclude that Cst was helpful in diagnosing early pulmonary abnormality in 50% of patients with normal spirometry. Among these patients Cst was a better index of abnormality than DLCO.