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Zhu et al in their elegant population-based cohort study investigated the development of systemic lupus erythematosus (SLE) in patients with idiopathic (immune) thrombocytopenic purpura (ITP) and demonstrated the significantly higher risk compared with the control population.1 They rightfully used sensitivity analysis and treatment data to improve the accuracy of clinical diagnosis. Despite this effort, the difficulty remains to compare epidemiological studies using self-reported diagnosis, health records or using classification criteria.2 In clinical practice, lack of a generally acknowledged diagnostic criteria might lead to SLE diagnosis of cases like undifferentiated connective tissue disease that may be treated similarly.3
Additionally, Zhu et al also provided important data on the association of antiphospholipid syndrome (APS) with ITP. They identified 20 cases of APS in the ITP group (2.77%) compared with 3 (0.02%) in the control group which was more frequent than any other autoimmune condition in their comorbidity list. The comorbidity list in table 1 included coronary artery disease and cerebral vascular accidents but not thrombosis, pulmonary embolism or pregnancy loss that might help further to identify additional risk of APS in these patients.1
APS is characterised by arterial and/or venous thrombosis and/or obstetric morbidities. Thrombocytopenia is the most common haematological manifestation of APS, although severe thrombocytopenia and bleeding are rare.4 Most importantly, moderate thrombocytopenia does not prevent the development of thrombosis.4 Data regarding the risk of thrombosis in patients with ITP and positive antiphospholipid autoantibodies (aPL) are controversial.4 We have previously shown in a controlled study that patients with ITP and positive aPL, especially positive for lupus anticoagulant, developed clinical features of APS (mostly thrombosis) during long-term follow-up.5
Fanouriakis et al further discussed the issue of assessment of patients with ITP from the point of systemic autoimmune disease and nicely stressed the importance of initial immunological testing including aPL in their accompanying editorial.6 We agree with Fanouriakis et al, and kindly suggest to add the APS (with or without SLE) among others to figure 1 as a significant possibility of another path of evolution of the disease with important consequences.
We would like to emphasise that in some patients with an initial diagnosis of ITP, features of SLE and/or APS may develop. A baseline assessment of patients with ITP for systemic clinical manifestations should be undertaken and relevant autoimmune serology including aPL profile should be searched.
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Competing interests None declared.
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