A longitudinal cohort study of Finnish patients with primary Sjögren's syndrome: clinical, immunological, and epidemiological aspects.

OBJECTIVE: To evaluate outcome in a cohort of Finnish patients with primary Sjögren's syndrome (pSS).

METHODS: Clinical and laboratory data from the time of diagnosis and follow up were collected from 110 patients with pSS (107 women, three men) diagnosed in 1977-1992 in central Finland. The standardised incidence ratio for cancers was determined as the ratio of the observed number of cases to the expected number based on regional population rates. Eighty one of the 93 patients still alive were interviewed, and clinical and laboratory examinations performed in 1994-1997.

RESULTS: The mean (SD) erythrocyte sedimentation rate (33 (22) v 45 (28) mm/1st h), serum IgG (18.8 (7.4) v 22.5 (8.5) g/l), and serum IgM (1.6 (1.1) v 2.0 (1.2) g/l) at the control visit were significantly (p<0.0001) lower than those at baseline. A similar change was observed in a subgroup of patients never treated with glucocorticosteroids or disease modifying antirheumatic drugs. Three non-Hodgkin's lymphomas were diagnosed (standardised incidence ratio 13; 95% confidence interval 2.7 to 38). In a logistic regression model, the patients with pSS with subsequent lymphoma were found to have higher baseline levels of serum beta2 microglobulin than the others (odds ratio 1.9; 95% confidence interval 1.1 to 3.4).

CONCLUSION: The results suggest that mean concentrations of serum IgG and IgM in patients with pSS decline with time, possibly reflecting diminishing inflammatory activity. As in previous studies, the incidence of non-Hodgkin's lymphomas in this cohort of patients with pSS was significantly higher than in the reference population.