Similarities and differences between primary and secondary Sjögren's syndrome.

Objective: To define the clinical, serological, and histopathological characteristics of primary (pSS) and secondary Sjögren's syndrome (SS).

Methods: Fifty subjects with pSS and 300 with connective tissue diseases (CTD; systemic lupus erythematosus 100, rheumatoid arthritis 100, scleroderma 100) were selected randomly from our patient registry. Selected patients were assessed for fulfillment of the American-European Consensus Group criteria for SS using a 3-phase approach: screening (European questionnaire, Schirmer-I test, wafer test), confirmatory (fluorescein staining test, nonstimulated whole salivary flow, anti-Ro/La antibodies), and lip biopsy (H&E and immunohistochemical staining for anti-CD20 and anti-CD45RO scored by morphometry).

Results: All patients with pSS and 65 with CTD met criteria for SS. Oral symptoms (pSS = 92% and secondary SS = 84%; p = 0.02), parotid enlargement (pSS 56%, secondary SS 9.2%; p < 0.001), and higher prevalence (pSS 82%, secondary SS 41%; p < 0.001) and titers of anti-Ro/La antibodies were more common in pSS. Extraglandular manifestations were similar in both groups, except for Raynaud's phenomenon, which was more common in those with secondary SS (pSS 16% vs secondary SS 41%; p = 0.001). These results remained after 3 different sensitivity analyses. The prevalence of focal infiltration was also similar in both SS varieties; however, a higher B:T cell ratio and higher expression of CD20 cells (2922 vs 607.5 positive cells; p < 0.001) were observed in pSS.

Conclusion: A higher frequency of oral symptoms and parotid enlargement and stronger B cell activity (autoantibody production and lymphocyte infiltration) were observed in pSS. Whether these results reflect a true difference between the 2 disease entities or derive from underlying variables remains uncertain.