1020: Cohort Study of European Ancestry, Geographic Region, Ambient Ultraviolet Irradiance and the Risk of Developing Polymyalgia Rheumatica among Women

Background/Purpose: Polymyalgia rheumatica (PMR) is one of the most common inflammatory rheumatic diseases among older women, but little is known of its etiology, and there are few established risk factors. We aimed to prospectively investigate the association between European ancestry, geographic region, ambient erythemal ultraviolet B light (UV) irradiance and PMR risk among women.

Methods: We used data from the Nurses’ Health Study (NHS), an ongoing longitudinal cohort of US female registered nurses (1980-2020; aged 34-59 years in 1980). Participants provided updated information on ancestry, residential information, lifestyle factors and newly diagnosed health conditions, such as PMR, on biennial questionnaires. Two board certified rheumatologists confirmed PMR self-reported diagnoses and dates of onset with medical records. Eligible participants were women aged 50 years or older and were free of PMR. Cox proportional hazards regression models, stratified by 2-year risk period and age, were used to estimate multivariable-adjusted hazard ratios (HRs) with 95% confidence intervals (95%CIs) for ancestry, region of residence and residential erythemal ambient UV irradiance in models that simultaneously adjusted for these factors and other covariates in relation to incident PMR.

Results: We followed 111,874 NHS women and accrued a total follow-up of 2,990,295 person-years (Table 1). Among them, 129 incident PMR cases were identified, and the mean age at diagnosis was 75.6 (SD=6.5) years. In multivariable-adjusted analyses (Table 2), having Scandinavian ancestry, compared to other European ancestry, was associated with more than a doubling of risk (HR: 2.35; 95%CI: 1.37, 4.05). Compared to living in the Midwest region, living in the Northeastern region was associated with a higher risk (HR: 1.89; 95%CI: 1.07, 3.34), while living in the Southern or Western regions were not significantly different (p >0.58). Greater ambient erythemal UV exposure based on residence was associated with a lower risk, with every 1 mW/m² increase in UV being significantly associated with a 2% lower risk (p=0.0045; HR=0.98; 95%CI: 0.96, 0.99; Figure 1). Those in the highest versus lowest UV quartile had a 73% lower risk (HR=0.27; 95%CI: 0.10, 0.72).

Conclusion: Scandinavian ancestry and living in Northeastern US were associated with a higher risk, while greater ambient UV erythemal irradiance was associated with a lower risk of PMR, indicating the important role of genetic and environmental factors in PMR etiology.