Carbon monoxide diffusing capacity as predictor of outcome in systemic sclerosis

In order to determine the predictive value of lung function studies for subsequent prognosis in systemic sclerosis, 71 patients with systemic sclerosis were followed up for a mean of five years after pulmonary function testing. A carbon monoxide diffusing capacity less than or equal to 40 percent of the predicted reference value was associated with only a 9 percent five-year cumulative survival rate compared with a 75 percent cumulative five-year survival in patients with a carbon monoxide diffusing capacity greater than 40 percent of predicted. An obstructive ventilatory defect was also associated with increased mortality, and all six patients with obstruction and a diffusing capacity less than 70 percent of the predicted died during the study period. Male gender, independent of abnormalities of pulmonary function, was also associated with a poor prognosis. Although it is not clear whether a severely impaired diffusing capacity is indicative of interstitial pulmonary fibrosis or pulmonary vasculopathy or is a marker of generalized vascular disease, a severely depressed carbon monoxide diffusing capacity is an important predictor of mortality in patients with systemic sclerosis.