Objectives: To define the incidence rate of primary Sjögren's syndrome (pSS) and the prevalence of extraglandular manifestations (EGMs) at the time of diagnosis of pSS in a prospective, population-based manner.
Method: This study included all consecutive patients referred to the Department of Rheumatology at Karolinska University Hospital for the investigation of incident pSS from 1 January 2007 to 31 December 2011. Investigation was according to the current criteria for pSS, and examination with a focus on the presence of EGMs was performed.
Results: Of the referred individuals, 199 out of 781 were diagnosed with pSS. We found an annual incidence rate of pSS in the Karolinska University Hospital catchment area of 3.1 [95% confidence interval (CI) 2.3-4.3] cases per 100 000 adult inhabitants. The female/male ratio of incident cases was 14/1 [frequency (female) = 0.93, 95% CI 0.89-0.96]. In our cohort, we noted lower figures for severe EGMs such as lung and neurological involvement than previously reported for prevalent pSS. The frequency of autoantibodies including antinuclear antibodies (ANA), anti-Ro/SSA, and anti-La/SSB was also lower compared to other cohorts. In our study, autoantibody-positive patients had cytopaenia significantly more often, and in patients older than 60 years primary biliary cirrhosis (PBC) was more common.
Conclusions: The incidence rate of pSS is 3.1 (95% CI 2.3-4.3) per 100 000 person-years. The prevalence of autoantibodies may be lower than previously reported, and at diagnosis, patients with pSS have few severe EGMs.