Evaluation of carbon monoxide diffusing capacity as an early detection of pulmonary involvement in rheumatoid arthritis patients without respiratory symptoms

Abstract

BackgroundThe risk of death for rheumatoid arthritis (RA) patients with interstitial lung disease (ILD) is three times higher than that in RA patients free from ILD. Therefore, this study was carried out to assess the value of carbon monoxide diffusing capacity (DLCO) in the early detection of pulmonary involvement in RA.Patients and methodsThis prospective study was carried out in 30 nonsmoker patients with RA (29 women and one men) ranging in age from 21 to 66 years, mean age 42.6 ± 1.9 years. All RA patients were clinically free from respiratory symptoms with normal chest radiograph. For all patients, spirometry and DLCO were performed.ResultsTwenty (66.67%) cases had a diffusion defect in DLCO; the defect was mild in 17 cases and moderate in three cases. The severity of DLCO differed significantly with the duration of RA and decrease in forced vital capacity (P < 0.05), but did not differ significantly with either the rheumatoid factor titer or the duration of methotrexate therapy (P > 0.05), although the use of methotrexate was higher among patients with abnormal DLCO. The severity of DLCO correlated significantly and inversely with the duration of RA (P < 0.05). A normal pattern of spirometry was the predominant pattern, followed by a restrictive pattern and small airway obstruction, whereas the obstructive pattern was the least observed.ConclusionThere is a high incidence of pulmonary involvement in RA patients, especially in those receiving methotrexate therapy. Pulmonary function testing, and more specifically DLCO, can serve as useful screening tools for the early detection of RA-ILD even in clinically asymptomatic patients with normal chest radiograph.