Epidemiology of primary systemic vasculitis in children: a population-based study from southern Sweden

Objectives: To estimate the annual incidence rate of paediatric primary systemic vasculitis (PSV) in a defined geographical area in southern Sweden.Methods: Potential cases of PSV [IgA vasculitis (IgAV, Henoch-Schonlein purpura), Kawasaki disease (KD), granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA), polyarteritis nodosa (PAN), and Takayasu's arteritis (TAK)] were identified in a comprehensive regional healthcare register. The study area is Skane, the southernmost county of Sweden (population 1.29 million; 21.4% aged <18years). Case records for children (0-17years) assigned a diagnosis code between M300 and M319 and/or D690 were reviewed to ascertain diagnosis. Only patients diagnosed between 2004 and 2014 were included.Results: In total, 556 patients with PSV were identified. The annual incidence rate per million children (95% confidence interval) was estimated to be 200 (183-217) for all PSV, 175.5 for IgAV (160-191), 20.1 for KD (14.9-25.4), 1.4 (0-2.8) for each of GPA and MPA, 0.7 (0-1.7) for PAN, and 0.4 (0-1.1) for each of EGPA and TAK. Among children aged <10years, 99.5% of cases were either IgAV or KD, both exhibiting a seasonal pattern paralleling infections. There were no deaths, but three cases of end-stage renal disease were noted, all in MPA.Conclusions: Vasculitis is relatively common during childhood. Mild cases associated with the infection season are most common in the youngest age groups, while during adolescence a substantial proportion has more severe forms of vasculitis.