Rheumatoid interstitial lung disease in Canterbury, Aotearoa New Zealand - A retrospective cohort study.

BACKGROUND: Rheumatoid arthritis associated interstitial lung disease (RA-ILD), is an important extra-articular manifestation of rheumatoid arthritis (RA). The frequency, risk factors, and prognosis of RA-ILD are incompletely understood. AIMS: To determine the prevalence and incidence, clinical characteristics and risk factors for development, and outcomes of persons with RA-ILD in the population of the Canterbury District Health Board (CDHB) catchment area. METHODS: Individuals aged ≥ 18 years with RA, resident in the CDHB catchment area between 1 January 2006 and 31 December 2008 (Period One), and 1 January 2011 to 31 December 2013 (Period Two) were identified by medical record review and followed until 30 June 2019. Individuals with RA-ILD as defined by pre-specified criteria were identified. The association between demographic and clinical characteristics and RA-ILD development and mortality was examined using Cox-proportional hazards models. RESULTS: The prevalence of RA-ILD per 100,000 was 10.97 (95 % CI 7.53,14.42) for Period One, and 14.74 (95 % CI 10.84,18.63) for Period Two. Among individuals evaluated for risk factors for RA-ILD development, the estimated cumulative incidence of ILD at 10 years was 4.47 % (95 % CI 3.14, 6.14). After adjusting for age, rheumatoid factor positivity (HR 3.73, 95 % CI, 1.32,10.56), extra-articular manifestations other than RA-ILD (HR 4.48, 95 % CI 2.36,8.48), and subcutaneous rheumatoid nodules (HR 4.66, 95 % CI 2.34, 9.26) were associated with increased risk of developing RA-ILD. The standardised mortality ratio for RA-ILD was 3.90 (95 % CI 2.55,5.72) compared to the general population. Extent of ILD on CT chest was associated with mortality (HR for >20% vs. < 20 % 4.47, 95 % CI 1.67,11.96). CONCLUSIONS: Clinically evident RA-ILD occurred in approximately 5 % of individuals with RA. Mortality was increased almost fourfold compared to the general population. Radiologic extent was the most important prognostic factor.

Rheumatoid interstitial lung disease in Canterbury New Zealand: prevalence, risk factors and long-term outcomes-protocol for a population-based retrospective study.

INTRODUCTION: Rheumatoid arthritis (RA) affects approximately 0.5%-1% of the general population. Clinically significant interstitial lung diseases (ILD) develops in just under 10% of people with RA, and subclinical disease is more common. Little is known about RA-ILD in New Zealand (NZ), or the number of persons with RA in Canterbury, NZ. This study aims to determine: (1) incidence and prevalence of RA, (2) incidence and prevalence of RA-ILD, (3) clinical characteristics and risk factors for the development of RA-ILD, (4) long-term outcomes of RA-ILD, in the population resident within the Canterbury District Health Board (CDHB) catchment area. METHODS AND ANALYSIS: Persons aged 18 years of age and older, and resident in the region covered by the CDHB with RA as well as RA-ILD will be identified by retrospective review of medical records. Prevalent as well as incident cases of RA between 1 January 2006 and 31 December 2008 and between 1 January 2011 and 31 December 2013 will be identified, and followed until 30 June 2019. Existing as well as incident cases of RA-ILD during this time will be identified. The association between the development of ILD and clinical characteristics and environmental exposures will be examined using Cox-proportional hazard models. Kaplan-Meier methods will be used to estimate survival rates for patients with RA-ILD. Mortality for people with RA and RA-ILD will also be compared with the general population of the CDHB. ETHICS AND DISSEMINATION: Data will be obtained by retrospective review of medical records. Deidentified patient data will be stored in a secure online database. Data on individual patients will not be released, and all results will only be published in aggregate. Ethical approval has been obtained from the University of Otago Human Research Ethics Committee (REF HD18/079). Results will be published in peer-reviewed medical journals and presented at conferences. TRIAL REGISTRATION NUMBER: ACTRN12619001310156; Pre-results.