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 (M1), and then also subjective outcomes (M2). 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 ([Formula: see text] = 0.12), while subjective outcomes had a strong negative impact and partly explained the variation in fatigue ([Formula: see text]= 0.27). Country of residence had a significant additional effect (increasing model fit to [Formula: see text] = 0.20 and [Formula: see text] = 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.