Clinical and histological features of patients with primary Sjögren's syndrome and autoimmune thyroiditis: a national multicentre cross-sectional study.

Primary Sjögren's syndrome (pSS) is frequently associated with autoimmune thyroiditis (AT). The aim of this study was to evaluate the prevalence of AT in a national cohort of pSS and to describe the clinical and histological phenotype of patients with pSS and associated AT. In this multicentre cross-sectional study, data from 2546 pSS were collected and the presence of AT was reported. In a subgroup, the histology of minor salivary glands was evaluated. Differences between pSS with and without AT were evaluated. A concomitant pSS and AT was detected in 19.6% of cases. Patients with pSS and AT displayed a lower prevalence of lymphoma, male sex and disease-modifying anti-rheumatic drugs (DMARDs) use and a higher prevalence of fibromyalgia, coeliac disease and hypergammaglobulinaemia. Multivariable analysis confirmed a higher prevalence of fibromyalgia and coeliac disease and lower use of DMARDs. In a subgroup of patients (n=232), a significantly higher focus score and number of foci was detected in pSS without AT (n=169) as compared to pSS with AT (n=54). This is the largest study evaluating the coexistence of pSS and AT. We confirm a high association between pSS and AT and describe the presence of a different phenotype characterized by a higher rate of celiac disease and fibromyalgia. Although not significant, the lower prevalence of both lymphoma and intake of DMARDs, along with a significantly lower focus score and number of foci, possibly suggest a more favourable outcome in concomitant pSS and AT which further deserve future investigations.