Immune thrombocytopenia in systemic lupus erythematosus: Prevalence, risk factors, and a novel predictive model for risk assessment.

Introduction: Immune thrombocytopenia (ITP) is a potentially severe manifestation of systemic lupus erythematosus (SLE) reported in 7-40% of SLE patients. ITP has been associated with a higher risk of organ damage and mortality.
Objectives: To describe which factors are associated with the presence of ITP in SLE patients.
Methods: Retrospective case-control study. Cases were defined as SLE patients who had ever developed ITP and were sex- and age-matched with two controls. A predictive model was constructed to identify SLE patients who were at risk of developing ITP.
Results: ITP prevalence in our SLE cohort was 8.35%. Cases had a higher frequency of hemolytic anemia, while controls had a higher prevalence of arthritis at SLE diagnosis. During SLE progression, cases tested positive for anticardiolipin, anti-β2-glycoprotein 1, and lupus anticoagulant antibodies more frequently. Cases received mycophenolic acid and azathioprine more often than controls and had a higher SLICC/ACR score. The model demonstrated a sensitivity of 87.53%, a positive predictive value of 81.92%, a specificity of 80.50%, area under the curve of 83.92%, a F1 of 83% and an overall accuracy of 83.68%. The variables that best explain the model were hemolytic anemia, arthritis, oral ulcers, Raynaud's phenomenon, low C4, low CH50, anticardiolipin and anti-β2GP1 antibodies.
Conclusion: SLE patients who develop ITP have a distinct phenotype characterized by more hemolytic anemia and less arthritis at SLE onset, and higher prevalence of antiphospholipid syndrome antibodies during SLE progression. This phenotype is associated with heightened organ damage and the need for more intensive therapies and stricter follow-up. Our predictive model has demonstrated an impressive ability to identify SLE patients at risk of developing ITP.
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