Background/Purpose: Comorbidity is common in patients with ANCA-associated vasculitis (AAV). However, this comorbidity and its burden over time remains unexplored. In this large multicenter study, we aimed to compare the risk of a broad set of comorbid diseases in AAV patients with the general population and identify potential temporal changes in the risk of their occurrence.

Methods: AAV patients fulfilling European Medicines Agency criteria were identified at seven hospitals in Scotland. Each was matched with up to five controls in the general population by age (±2 years), sex and geography. Diagnoses of selected comorbidities were retrieved from the Inpatient or Day Case Hospitalisations Database using International Classification of Disease codes. Cohorts were followed from the date of AAV diagnosis until death or 02/28/2017, whichever came first. Comorbidity incidence was assessed using modified Poisson regression. Temporal patterns in comorbidity incidence were assessed using discrete regression analysis at the following intervals: 2-<5 years, 5-<10 years and 10+ years after follow-up. 

Results: A total of 543 AAV (53.5% male) patients were matched with 2672 general population controls. The median (interquartile range) follow-up time was 5.1 (2.5 to 9.4) years. Overall, after AAV diagnosis, these patients were at a higher risk of developing the following comorbid diseases compared to the general population (Incidence Rate Ratio; 95% Confidence Interval): osteoporosis (8.0; 4.6-14.2), pulmonary circulation disorders (5.5; 3.3-9.1), hypothyroidism (3.4; 2.0-6.0), valvular disease (3.0; 2.1-4.4), hypertension (2.4; 1.8-3.1), cardiac arrhythmias (2.2; 1.5-3.1), chronic pulmonary disease (2.2; 1.6-3.1), diabetes mellitus (2.1; 1.4-3.0), and major cardiovascular events (1.4; 1.1-1.9). Temporal analyses showed that differences in risk were most apparent in the first two years following diagnosis, and they tended to reduce, if not disappear, for many comorbidities over time (See Figure 1).

Conclusion: To our knowledge, this is the first study to comprehensively examine the breadth and timing of comorbidity risk in AAV. Our findings showed that AAV patients face an increased risk of comorbidity, especially within the first two years of diagnosis. These data should help inform the management of these patients. Further analysis incorporating prescription data might help explain the reduction of risk over time.

Figure 1. Incidence of comorbid diseases in AAV compared with that in the general population