Impact of diabetes mellitus on mortality in patients with giant cell arteritis.

Objectives: This study aimed to investigate the impact of diabetes mellitus (DM) on the risk of mortality in patients with giant cell arteritis (GCA). Methods: This Danish nationwide cohort study included patients diagnosed with both GCA and DM, who were matched 1:3 with patients with only GCA or DM, on sex and year of birth. The Pseudo-observation method and Cox regression were used to evaluate the cumulative incidence proportion (CIP), risk difference (RD), and relative risk of mortality after 6 months and 5 years. Also, time-dependent hazard ratios (HR) were made to assess the impact of predefined HbA1c categories on the risk of mortality. Results: Among 3674 cases, the CIP of mortality was 8.1% (7.1-9.1) at 6 months and 34.6% (32.7-36.4) at 5 years. Compared with patients with GCA only (n = 10,311), the RD was 5.5% (4.5-6.5) at 6 months and 15.1% (13.3-17.0) at 5 years. Compared with patients with DM only (n = 11,020), the RD was 4.9% (3.9-5.9) and 6.5% (4.7-8.3). The adjusted HR for mortality was significantly higher in patients with elevated HbA1c, especially after 5 years of follow-up. Conclusions: Having both GCA and DM was associated with a higher mortality risk compared with either condition alone, especially in the initial phase after diagnosis. High HbA1c increased the risk of 5-year mortality in both patients with GCA and DM and GCA alone, suggesting glycaemic control could be relevant in this population.