Does rain really cause pain? A systematic review of the associations between weather factors and severity of pain in people with rheumatoid arthritis

Objective: To examine the association between weather and pain in rheumatoid arthritis (RA). Methods: Systematic review of longitudinal observational studies (up to September 2009) with data on the association between weather variables and severity of pain in RA. The methodological quality was rated independently by the two authors according to an adapted Newcastle-Ottawa Scale. We analyzed the data on an aggregated (group) level with a meta-analysis of correlations between pain and weather, and at an individual level as the proportion of patients for whom pain was significantly affected by the weather. Results: Nine studies were included. Many different weather variables have been studied, but only three (temperature, relative humidity and atmospheric pressure) have been studied extensively. Overall group level analyses show that associations between pain and these three variables are close to zero. Individual analyses from two studies indicate that pain reporting in a minority (<25%) of RA patients is influenced by temperature, relative humidity or atmospheric pressure. We were not able to relate the findings to methodological quality or other aspects of the studies. Conclusion: The studies to date do not show any consistent group effect of weather conditions on pain in people with RA. There is, however, evidence suggesting that pain in some individuals is more affected by the weather than in others, and that patients react in different ways to the weather. Thus, the hypothesis that weather changes might significantly influence pain reporting in clinical care and research in some patients with RA cannot be rejected. (C) 2010 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.