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.
Evaluation of the literature.
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.
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.