Giant cells in temporal artery biopsies and the risk of large-vessel involvement in patients with giant cell arteritis.

Objectives: Giant cell arteritis (GCA) is a systemic disease with variable vascular involvement. The objective was to investigate predictors of time-dependent large vessel involvement (LVI) in a population-based cohort of patients with GCA.

Methods: GCA patients with positive temporal artery biopsies (TAB) between 1997- 2010 were identified through a regional pathology register. A structured review of histopathology reports and relevant imaging studies was performed. Cases with LVI through July 2016 were identified. Patients were followed to first LVI, death, migration from the area or July 29, 2016. Event free survival by clinical and histopathologic features was estimated using the Kaplan-Meier method. Potential predictors of LVI were examined using Cox regression models.

Results: A total of 274 patients were included. The mean age at GCA diagnosis was 75.7 years. Fifty-one patients (19 %) had documented LVI during the follow-up, corresponding to an incidence rate of 2.4/100 person-years. The median time from GCA diagnosis to the diagnosis of LVI was 4.5 years (interquartile range 0.6-7.4). Thirty-four patients had aortic involvement (67% of those with LVI; 12% of all GCA cases). Survival free of LVI was longer in patients with giant cells in the TAB (75th percentile 14.0 vs 6.7 years; p=0.014). In age-adjusted analysis, the presence of giant cells in the TAB was associated with reduced risk of LVI (hazard ratio 0.48; 95 % confidence interval 0.27-0.86).

Conclusions: The negative association with giant cells in the TAB suggests that patients with LVI constitute a subset of GCA with particular disease mechanisms.