Background Exhaled NO (eNO) is elevated in airway and parenchymal lung diseases. The levels of eNO in rheumatoid arthritis associated ILD (RA-ILD) has not been studied before.
Objectives The main objective of this study was to compare the concentration of eNO in RA patients with and without ILD.
Methods Eighteen patients, 7 with RA-ILD diagnosed on HRCT chest performed in the preceding 2 years, and 11 with RA not known to have ILD attending the respiratory or rheumatology clinics at Nottingham University Hospitals NHS Trust, UK participated in this study. All participants met the 1987 American College for Rheumatology classification criteria for RA. Patients with RA overlap syndromes, pulmonary hypertension, chronic obstructive airway disease, and those on home oxygen, oral nitrates or sildenafil were excluded. The study was approved by the Derbyshire Research Ethics Committee, UK. Information was collected about disease and demographic characteristics, and detailed clinical examination including 28-tender and swollen joint counts (TJC and SJC) was carried out. All patients completed the St Georges’ Respiratory Questionnaire (SGRQ). eNO was measured in parts per billion (ppb) (NIOX-MINO, Aerocrine, Sweden), and spirometry was performed. TJC, SJC, patients’ and physicians’ global assessment were used to calculate clinical disease activity index (CDAI). Independent sample t–test and chi-square test were used to compare continuous and categorical variables.
Results There were no differences in age, gender, smoking status, disease duration, DMARDs, and CDAI between RA patients with and without ILD. No patient with RA alone had clinical signs of ILD. None of the RA patients, and 6 of the seven patients with RA-ILD were on oral or inhaled corticosteroids. There was no difference in eNo concentration between patients with RA and RA-ILD (mean difference (95%CI) -2.42 (-6.64 – 11.50) ppb). Patients on biologics had a trend towards higher eNO than those on conventional DMARDs (mean difference (95%CI) 8.78 (-0.04-17.60), p=0.05). Although non-significant, there was a modest correlation between FEV1/FVC and eNO (r= -0.43, p=0.08). However, there was no correlation between FVC and eNO (p=0.42). Total SGRQ score was significantly lower in patients with RA-ILD than in patients with RA alone (mean difference (95%CI) 42.50 (32.40-52.59)). Although not statistically significant, RA-ILD associated with other extra-articular manifestations (kerato-conjunctivitis sicca 3, anemia of chronic disease 1, rheumatoid nodules 1, episcleritis/scleritis 1) compared to RA alone (kerato-conjunctivitis sicca and rheumatoid nodules 2, episcleritis/scleritis 1), p=0.09.
Conclusions There was no difference in eNo level between RA and RA-ILD. However, the high eNO level in patients on biologic agents is an interesting finding which warrants further study. eNO levels seem to predict airway hyper-responsiveness in RA. The lack of difference in eNO levels between RA and RA-ILD may be due to the fact that we measured the overall eNO concentration, and that this was not separated between the airway and alveolar compartments. However, it may be a type 2 error. Further studies examining the alveolar and airway components of eNO in patients with RA and RA-ILD are required.
Disclosure of Interest None Declared