Background/Purpose: In this study, we sought to perform an unsupervised hierarchical clustering analysis in a large cohort of antiphospholipid antibodies (aPL) positive patients, to identify the aggregation of patients into different subgroups sharing common characteristics in terms of clinical and laboratory phenotypes.

Methods: We applied a hierarchical cluster analysis from the multiple correspondence analysis to determine subgroups of patients according to clinical and laboratory characteristics in patients with confirmed aPL positivity who presented to our outpatient clinics 2006 to 2018.

Results: We included in this observational, retrospective, and multicentre study 486 patients (403 [83%] women; median age, 41[18-74] years; mean age, 41.7 years±26) with confirmed aPL. Among those 486 subjects, 5 clusters of patients emerged. Cluster 1 (N=150) presented with  thrombotic events (65% with a venous thrombosis) in the absence of a confirmed diagnosis of systemic  lupus  erythematosus(SLE). Up to 85% of patients from Cluster 1 were positive for more than one aPL, triple aPL positivity was found in 35% of the patients, the highest rate observed among the different subgroups(p< 0.01).  All the patients from Cluster 2 (N=91 patients,  84.4% were female) had a confirmed diagnosis of SLE and presented with ANA positivity. These patients had the highest rate of anti-dsDNA positivity(as high as 92%), and up to 64.6% of them presented hypocomplementemia(p< 0.01). Cluster 3 included 79 women who suffered from pregnancy morbidity, with consecutive early miscarriages in up to 45.6% of the cases. Multiple aPL positivity was found in 30%, with triple positivity in 3.8%, rates significantly lower when compared to Cluster 1(85% and 35%v.s.30 and 4% for multiple and triple positivity, respectively,p< 0.01). Cluster 4 included 67 patients (13.8% of the total), 28(42%) of whom with defined diagnosis of APS. Thrombotic events were observed in 16 out of 67(24%) patients. Patients in this group had the highest rate of cytopenia, with thrombocytopenia as high 42%. None of them had anti-dsDNA antibodies positivity. Multiple aPL positivity was found in 72% of the patients, with triple positivity in 4.5%,rate significantly lower when compared to Cluster 1(85% of multiple aPL and 35% of triple aPL positivity) and Cluster 2(83% for multiple aPL and 22% triple aPL positivity, p< 0.01). Cluster 5 included 94 subjects. No subjects in this group had a history of thrombosis or pregnancy morbidity. They were all negative for ANA and anti-dsDNA, with normal leukocytes and platelets count.

Conclusion: This study identified 5 clusters emerging from unsupervised analysis. Clusters 1, 2, 3 and 5 corresponded to well-known entities, such thrombotic Primary APS, Secondary APS, obstetric APS and aPL carriers, respectively. Cluster 4 might represent a bridging condition between patients with pure PAPS and defined SLE, with lower thrombotic risk when compared to Primary APS but higher general features such as ANA and cytopenia (mainly thrombocytopenia), representing a group that might benefit of different therapeutic approaches rather than only counterbalancing the pro-thrombotic status.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/identifying-phenotypes-of-patients-with-antiphospholipid-antibodies-results-from-a-cluster-analysis-in-a-large-cohort-of-patients/