A seasonal pattern in the onset of polymyalgia rheumatica and giant cell arteritis? A systematic review and meta-analysis

Objectives: Studies on the seasonality of onset of polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) have shown conflicting results. The aim of this systematic literature review and meta-analysis is to determine from aggregated data whether there is a seasonal distribution for these diseases. Methods: A literature search was performed using Pubmed Central and Embase scientific databases. The incidences per 6-month periods, season or month of onset, that were reported in the studies were summarised in tables considering the two diseases as separate conditions or together. The Incidence Rate Ratio (IRR) for the cold period versus the warm period was pooled across studies by random effects meta-analysis weighed by inverse variance. Funnel plots and Egger test were used to explore possible publication biases. A sensitivity analysis was performed to weigh articles with a disproportionate number of patients compared to the rest. Results: In the scientific literature 22 suitable papers were found: 6 on PMR with 803 patients, 11 on GCA with 2,807 patients, and 5 studies considering both diseases with 19,613 patients. There was considerable heterogeneity amongst studies regarding their quality, the classification criteria used, and the definition of onset of symptoms. No seasonal aggregation was found for GCA and PMR. The pooled IRR estimate of the meta-analysis (1.13[0.89,1.36]) showed a non-significant, higher frequency of diseases onset in the warm season. Conclusions: Our meta-analysis did not confirm a seasonal onset for PMR and GCA.