Interstitial lung disease in patients with rheumatoid arthritis

Objective To investigate the prevalence and clinical characters of rheumatoid arthritis-interstitial lung disease (RA-ILD). Methods Eighty-five inpatients with rheumatoid arthritis (RA) were studied. Serum rheumatoid factor (RF), C reactive protein (CRP), immunoglobulin (IgG, IgA, IgM), and complement (C3, C4)were measured by immunonephelometry. Antinuclear antibodies (ANAs) and anti-ENA antibodies were measured by indirect immunofluorescence technique and Western blot. Serum laminin (LN), type Ⅳ collagen (Ⅳ·C), hyaluronic acid (HA) and type Ⅲ procollagen (PcⅢ) were measured by radioimmunoassay. Arterial gas was analyzed including PaO2, PaCO2, and PA-aO2. The following pulmonary function tests were performed: tidal volume (VT), maximal vital-capacity (VCmax), forced vital capacity (FVC), one second forced expiratory volume (FEV1), FEV1/FVC, maximal midexpiratory flow (MMFF), maximal voluntary ventilation (MVV), and diffusing capacity CO (DLCO). Radiology examinations included chest X radiographs, hand radiographs and chest HRCT. Results ① The incidence of RA-ILD was 32.9%. RA-ILD frequently occurred in male with old ages with and long disease duration. ② The levels of LN and PcⅢ were significantly higher than those in non-ILD. ③ The damage of lung function was mainly the decreased DLCO and restricted ventilatory function abnormalities. ④ HRCT abnormal findings included interlobuar septal thickening, thickening of bronchovascular bundles, subpleural lines, reticular appearances, ground glass capacity and honeycomb changes. HRCT was more sensitive than chest radiography. ⑤ According to clinical characters, pulmonary function tests, chest plain radiographs and HRCT, we classified RA-ILD into: preclinical (n=11), acute pneumonitis (n=7) and chronic interstitial disease (n=10). Conclusion The incidence of RA-ILD is associated with the activity and severity of RA. Serum LN and PcⅢ, DLCO and HRCT are important in finding early disease. The clinical classification may provide some help for treatment and follow-up study.