A clinical prediction rule for lymphoma development in primary Sjögren's syndrome

Objective: To develop and validate a practical prediction rule for the progression from primary Sjögren's syndrome (pSS) to B cell non-Hodgkin's lymphoma (B cell NHL) based on the combination of routinely available clinical and serological disease variables. Methods: The case records of 563 patients with pSS were reviewed, and their demographic, clinical, and immunologic features were collected. Multivariate logistic regression analysis was performed to identify independent risk factors for lymphoma development and to create a propensity score for discrimination between patients at risk of B cell NHL and those patients not at risk. The model was internally validated by resampling procedures. Results: Out of 563 patients with pSS, 387 fulfilling the American European Consensus Group criteria (12 with B cell NHL, 375 without B cell NHL) were included in our study. Salivary gland enlargement (p = 0.001), low C3 (p = 0.035) and/or C4 levels (p = 0.021), and disease duration (p = 0.001) were identified as independent risk factors for B cell NHL in pSS. The optimal threshold of the propensity score was determined at Y = 4.26, which allowed us to identify patients who develop B cell NHL with a sensitivity of 78% and specificity of 95%. The leave-one-out cross-validated prediction error was 6%, and the median bootstrapped sensitivity and specificity were 71% and 95%, respectively. Conclusion: We created a "bedside" prediction model for the identification of patients with pSS who are at risk for B cell NHL, which revealed an excellent discriminative ability and a good internal and external reproducibility.