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.
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.
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.
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.