Isolated diffusing capacity reduction in systemic sclerosis

Abstract

Objective. To determine the long‐term outcome of patients with systemic sclerosis (SSc) and an isolated reduction in the diffusing capacity for carbon monoxide (DLco) at the time of initial evaluation. Methods. Patients with an isolated reduction in DLco (i.e., normal forced vital capacity [FVC] and normal ratio of the forced expiratory volume in one second [FEV 1] to the FVC) on initial evaluation were identified from among 815 patients with SSc who were carefully followed up throughout their illness. We requested that patients have repeat pulmonary function testing (PFT), and the outcomes of these tests, as well as cardiopulmonary and survival outcomes, were determined. Results. An isolated reduction in DLco, with a normal FVC was detected in 152 (19%) of the 815 patients. A subset of those with an isolated reduction in DLco (11%) developed isolated pulmonary hypertension and had severely reduced survival rates. Pulmonary hypertension was strongly associated with an initial DLco of < 55% of predicted normal and a FVC (% predicted)/DLco (% predicted) ratio of > 1.4. Among all patients in whom this ratio was > 1.4, 22% developed isolated pulmonary hypertension, compared with only 2% of those whose ratio was <1.4 (P < 0.01). Of the 152 patients with isolated DLco reduction, 73 (48%) underwent PFTs a mean of 5.4 years (range 2.0–13.2) after the initial PFT. Only 6 (8%) of these 73 patients ever had serious pulmonary disease: 5 had isolated pulmonary hypertension, and 1 had severe pulmonary fibrosis. Half of the patients with a low initial DLco demonstrated a significant improvement (>20%) at followup testing that could not be explained by the demographic, clinical, or laboratory findings at the first visit. Conclusion. Isolated reduction in DLco is a frequent abnormality in SSc. Overall, it is associated with a good prognosis for survival and for pulmonary morbidity. A small subset of patients (11%) who have a very low DLco (<55% of predicted) have developed isolated pulmonary hypertension, all of whom had limited scleroderma.