Interstitial Lung Disease and its Associations in Rheumatoid Arthritis: Data from a District General Hospital in Sri Lanka

CONTEXT: Interstitial lung disease (ILD) is a frequent pulmonary manifestation of rheumatoid arthritis (RA). No Sri Lankan studies have determined the prevalence of lung disease in RA and its associations. AIMS: To find the prevalence of ILD in RA and its association with rheumatoid factor (RF), erosions, Disease activity score in 28 joints (DAS 28), disease duration, Body mass index(BMI), erythrocyte sedimentation rate (ESR), smoking, and also to determine the prevalence of lung disease with demographic factors like age, sex, and income. SETTINGS AND DESIGN: Questionnaire based retrospective study at a District General Hospital in Sri Lanka. MATERIALS AND METHODS: Diagnosed RA patients included through convenient sampling as it was a simple method that could facilitate data collection in a short duration. Since all patients with a diagnosis of RA were eligible, all consecutive patients with a diagnosis of RA at the rheumatology clinics were included in the study. To reduce the bias a large sample of patients were used as well as patients attending different rheumatology clinics were included and also patients who were referred to the hospital from peripheries were included in the study. The calculated sample size was 384 and according to patient numbers attending clinics, a period of 6 months was decided to select the study sample. STATISTICAL ANALYSIS USED: Chi-Square calculation and logistic regression analysis using Minitab 17 software. RESULTS: From 384 patients, the prevalence of ILD was 14.58%, been 5.4% in early RA (<2 years disease duration). Mean age of ILD group was 52.94 years (95% CI 64.66-41.22). Mean RA duration was 7.69 years (95% CI, 2.38-12.99). Male to female sex ratio of RA was 1:7, and that of ILD was 2:9. DAS 28 was 4.58 (95% CI, 3.48-5.68). Statistically significant associations were noted with ILD and DAS 28 (P = .0006), ESR (P = .005), RF (P = .03), erosions (P < .00001), and smoking (P < .05). Mean BMI was 22.67 kg and 75.78% had low income (<50 000 rupees/month = 327 US $). CONCLUSIONS: ILD significantly associates RA severity indices like DAS 28, ESR, erosions, RF, and also with smoking. No significant association was found with BMI or gender difference. Therefore, disease severity indices could be used to predict progression to ILD in RA.