Background/Purpose: To determine whether there is a seasonal peak onset of polymyalgia rheumatica (PMR). We examined the seasonal variability of PMR in a geographically-defined population.

Methods: In a geographically defined population, we retrospectively identified all incident cases of PMR between January 1, 1970, and December 31, 2014. Detailed review of all individual medical records was performed. All patients fulfilled EULAR/ACR classification criteria for PMR. Incidence rates were age and sex adjusted to the US white 2010 population. Seasonal variation was compared using quasi-Poisson regression models to account for overdispersion.

Results: The cohort included 786 cases of incident PMR (65% female; mean age 73.3 years). Overall, patients in this cohort were more likely to have incident PMR in the spring season with age- and sex-adjusted incidence rates (per 100,000 population) of 17.2 for spring compared with 13.8 for winter, 15.5 for summer and 15.2 for autumn, but this difference did not reach statistical significance (p=0.21). However, subgroup analysis by decade revealed that incidence of PMR was significantly higher (p=0.013) in the spring season during 2000-2014 with an age-adjusted and sex-adjusted incidence rate pr 100,000 of 21.1 compared with winter (13.6), summer (18.3) and autumn (15.3) [Figure].

Figure. PMR incidence rates by season and decade (1970-79 open circles, 1980-89 squares, 1990-99 filled circles, 2000-14 triangles) among Olmsted County, Minnesota residents in 1970-2014

Conclusion: Incident PMR is more common in the spring season. This pattern is more pronounced in recent years. Further study is needed to understand the potential etiological and clinical significance of this finding.