Seasonal onset of polymyalgia rheumatica: correlations with the pattern of clinical presentation, disease severity and outcome in 383 patients from a single centre.

Polymyalgia rheumatica (PMR) is an inflammatory disorder, more common in the elderly, characterised by girdle pain and stiffness, constitutional symptoms and raised serological markers of inflammation. Studies on the seasonality of onset of PMR have shown conflicting results, possibly due to the different diagnostic criteria and onset recognition. In this study, the month of onset of PMR was evaluated in patients originating from one geographical area, visited by the same clinician. In 383 PMR patients (245 women, median age 73 years, range 47-92 years) examined between 1990 and 2014, PMR was diagnosed according to Bird's criteria. The month of onset was recorded systematically during the patient's interview. Clinical features initially recorded included the location of joint involvement, the coexistence of temporal arteritis (TA) or peripheral arthritis, and the type of onset (acute if reported of 72h or less). Patient follow-up, PMR severity and outcome were also recorded throughout the study. We failed to identify any peak month (p=0.93) or season (p=0.45) for the onset of PMR. Timing of onset did not correlate with the clinical features, severity or outcome of PMR. Only when patients were also affected by concomitant TA, the onset of PMR was more often seen in autumn (p=0.02). Patients with PMR onset in autumn also has a greater risk of developing TA during their follow-up (p=0.03). By multiple regression, the only outcome predicted by autumn onset was the use of methotrexate (p=0.039). PMR showed no seasonality of onset, except for the subset associated with TA. A risk factor with seasonal variation is suggested for the pathogenesis of this form of PMR.