Objective: To review the data on the epidemiology of polymyalgia rheumatica (PMR), in particular geographical and temporal differences in incidence and its risk factors including the actinic hypothesis.
Methods: Evaluation of the literature.
Results: Epidemiological data show that the incidence of PMR varies between 12.7/100,000 in Italy and 112.6/100,000 in Norway with a geographical gradient of increased frequency in the northern hemisphere. The incidence of PMR and giant cell arteritis (GCA) have increased in recent years. This observation may be related to a greater awareness of the disease but also to real epidemiological changes. Risk factors for PMR/GCA include infections, smoking, sun exposure, and nulliparity.
Conclusion: Epidemiological studies have helped to unravel the etiopathogenic factors at work in PMR/GCA. More data are needed on the correlation between the incidence of PMR/GCA and epidemics of infectious diseases and on environmental and biological risk factors.