In rheumatoid arthritis, country of residence has an important influence on fatigue: results from the multinational COMORA study

Objectives. To investigate the relationship between country of residence and fatigue in RA, and to explore which country characteristics are related to fatigue.

Methods. Data from the multinational COMORA study were analysed. Contribution of country of residence to level of fatigue [0-10 on visual analogue scale (VAS)] and presence of severe fatigue (VAS >= 5) was explored in multivariable linear or logistic regression models including first socio-demographics and objective disease outcomes (M-1), and then also subjective outcomes (M-2). Next, country of residence was replaced by country characteristics: gross domestic product (GDP), human development index (HDI), latitude (as indicator of climate), language and income inequality index (gini-index). Model fit (R-2) for linear models was compared.

Results. A total of 3920 patients from 17 countries were included, mean age 56 years (S.D. 13), 82% females. Mean fatigue across countries ranged from 1.86 (S.D. 2.46) to 4.99 (S.D. 2.64) and proportion of severe fatigue from 14% (Venezuela) to 65% (Egypt). Objective disease outcomes did not explain much of the variation in fatigue (R-M1(2) = 0.12), while subjective outcomes had a strong negative impact and partly explained the variation in fatigue (R-M2(2) = 0.27). Country of residence had a significant additional effect (increasing model fit to R-M1(2) = 0.20 and R-M2(2) = 0.36, respectively). Remarkably, higher GDP and better HDI were associated with higher fatigue, and explained a large part of the country effect. Logistic regression confirmed the limited contribution of objective outcomes and the relevant contribution of country of residence.

Conclusion. Country of residence has an important influence on fatigue. Paradoxically, patients from wealthier countries had higher fatigue.