Lung diffusing capacity for nitric oxide was more sensitive than lung diffusing capacity for carbon monoxide at detecting functional impairment in the absence of radiologic or hemodynamic alterations of interstitial lung disease in patients with systemic sclerosis, according to researchers at the University of Padova in Italy.
Thirty-seven patients with systemic sclerosis (SSc) were recruited through the hospital and were diagnosed based on the American Rheumatism Association criteria. Patients who smoked or had other lung diseases, or who received immunosuppressants or more than 10 mg of prednisone daily, were excluded. A group of 21 healthy, nonsmoking control participants matched for age and gender was also enrolled. Demographics were comparable in each group, although the patient group was slightly older.
Within 4 months prior to the study, all patients with SSc underwent high resolution CT (HRCT) and echocardiography. Patients with a HRCT score of 5 or greater were classified as having parenchymal lung disease. A 2-D technique was performed, and pulmonary arterial systolic pressure (PAPs) was evaluated by Doppler echocardiography. Patients were diagnosed with pulmonary arterial hypertension (PAH) in the presence of PAPs values above 50 mm Hg, and patients with PAPs values between 37 mm Hg and 50 mm Hg underwent right heart catheterization.
Complete pulmonary function tests in both groups included spirometry, assessment of lung diffusing capacity for carbon monoxide (DLCO) and for nitric oxide (DLNO), and conductance of alveolar-capillary membrane (Dm) and pulmonary capillary blood volume (Vc) were determined.
Seventeen of the 37 patients showed HRCT scores below 5 and did not have PAH. Scores of 5 or greater were seen in 20 patients with SSc, 60% of whom were in the group II WHO classification and 40% were in group III. No significant reduction in lung function was seen in the patient group compared with the control group, but lower total lung capacity (TLC) was observed in patients with SSc, according to the researchers.
Results showed all of the patients tested positive for antinuclear antibodies, with anti-Scl70 present in 15 patients, anti-centromere positive in 13 patients, anti-RNA polymerase III in three patients and nonspecific pattern present in six patients.
Compared with the control group, patients with SSc had significantly reduced DLNO, and patients with concurrent interstitial lung disease had a highly significant reduction in DLNO. Multivariate statistical analysis of variables Dm, Vc, PAH and others showed that DLNO displayed higher sensitivity for detection of lung function impairment than DLCO, according to the researchers. - by Shirley Pulawski
Disclosure: The researchers report no relevant financial disclosures.