Epidemiology of biopsy-proven giant cell arteritis in South Australia

Background/Aim: To determine the epidemiology and clinical features of biopsy-proven giant cell arteritis (GCA) in South Australia (SA). Methods: Patients with biopsy-proven GCA were identified from pathology reports of temporal artery biopsies at SA Pathology laboratories, from 1 January 1992, to 31 July 2011. Epidemiological data were collected through patient questionnaires and standardised case note reviews. Incidence was estimated using Australian Bureau of Statistics population data for SA. Seasonality was analysed by Cosinor analysis, and time-to- event analysis was performed for the duration of steroid use. Results: There were 314 cases of biopsy-proven GCA (72% female). The mean age at diagnosis of GCA was 78 years (interquartile range 72-82). The estimated population incidence for people over 50 was 3.2 per 100000 person years. The female:male incidence ratio was 2.3 (P < 0.001), and incidence increased with each age decade. There was evidence of seasonal variation (P = 0.015), with higher rates observed in the summer months. Clinical data were available for 163 patients (68% female, median age 78 years). The most common presenting clinical features were temporal headache (74%), visual disturbance (68.4%), jaw claudication (59.3%) and symptoms of polymyalgia rheumatica (56%). The median initial steroid dose was 60mg, with median duration of steroid use 4.5 years. Corticosteroid side-effects were common, affecting 89%, with 34% reporting five or more. Conclusions: This is the first epidemiological study of Australian biopsy-proven GCA patients. Age at onset and gender associations were similar to other Western populations. There was a high burden of steroid use in these patients.