Mortality and causes of death in primary Sjögren's syndrome: A prospective cohort study

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Abstract
Objective This study was undertaken to analyze standardized mortality ratios (SMRs) and causes and predictors of death in primary Sjögren's syndrome (SS) diagnosed according to 3 different classification criteria sets (the Copenhagen criteria, the European criteria, and the American-European consensus criteria (AECC). Methods A linked registry study using information from the Malmö Primary SS Registry combined with the Swedish Cause-of-Death Registry was performed, and SMRs were calculated. Kaplan-Meier survival curves and log rank tests were used to compare survival probability between subgroups of patients with primary SS. Cox regression analysis was used to study the predictive value of various laboratory findings at the time of diagnosis. Results Four hundred eighty-four patients with a median followup of 7 years (range 1 month to 17 years 11 months) were included. The SMR for those fulfilling the AECC (n = 265) was 1.17 (95% confidence interval [95% CI] 0.81–1.63). Thirty-four deaths occurred in this group of patients. Excess mortality was found only for lymphoproliferative malignancy (cause-specific SMR 7.89 [95% CI 2.89–17.18]), corresponding to 2.53 excess deaths per 1,000 person-years at risk. In those not fulfilling the AECC (n = 219), 14 deaths occurred, the SMR was 0.71 (95% CI 0.39–1.20), and no excess mortality due to any specific cause was found. Hypocomplementemia, defined as C3 and/or C4 values in the lowest quartile of the SS patients' values at the time of diagnosis, was a significant predictor of death, mainly due to lymphoproliferative malignancy. Conclusion No increased all-cause mortality could be detected for patients with primary SS compared with the general population. When subgroups of primary SS were compared, excess mortality due to lymphoproliferative malignancy was found in patients fulfilling the AECC, the strongest predictor for unfavorable outcome being low C3 and/or C4 levels at the time of diagnosis.

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