Background Antiphospholipid Syndrome (APS) is an acquired immune disorder defined by the presence of thrombosis and/or pregnancy morbidity together with the presence of positive antiphospholipid antibodies (aPL) (anticardiolipin antibodies (aCL), anti -beta2 glycoprotein I (AB2GPI) and/or lupus anticoagulant (LA). There is a clear relationship between aPL and some events not included in the clinical criteria such us the hematologic manifestations. Among these, thrombocytopenia has been described in 20–50% of patients with APS. Although thrombocytopenia in APS is usually not serious, its impact on the clinical curse of the diseasesis unknown.
Objectives a) To study the probability of developing clinical APS in patients with positive aPL and thrombocytopenia b) To identify potential risk factors for the development of APS. c) To study the association of thrombocytopenia with aPL autoantibodies.
Methods Retrospective study of patients with positive aPL on at least 2 times, separated by a minimum of 12 weeks in medium or high titers without fulfilling clinical criteria for APS. The patients were selected from the database of the Department of Immunology of a tertiary hospital (1999–2004). Thrombocytopenia was defined as a platelet count ≤100000 platelets/L. We excluded patients with other causes of thrombocytopenia.
Results 17 of 138 (12%) patients in the study had thrombocytopenia (mean platelet count 60,000/mm3). Ten patients received oral glucocorticoids. Only 2 patients with <5.000 platelets/mm3 were treated with intravenous gammaglobulins. Smoking was more common in patients with thrombocytopenia (47.1% vs 24%; p=0.044). The risk for thrombocytopenia was almost 3 times higher in smokers (OR 2.8; 95%CI 1.0–8.0; p=0.044).
We found no statistically significant relationship with the distribution of the different antibodies, except for AL (OR 13.5, 95%CI 3.8–47.6; p<0.001). Patients with 2 and 3 positive antibodies were more likely to develop thrombocytopenia than those with a single antibody (OR 12.4 and 50.8 respectively; p=0.002 and p<0.001).
After a mean follow-up of 146±60.3 months, 5 patients with thrombocytopenia (29.4%) developed thrombosis (4 arterial: 1 anterior ischemic optic neuropathy, 1 transient ischemic attack, 1 stroke and 1 acute myocardial infarction, and 1 deep venous thrombosis of the lower limbs with secondary pulmonary embolism), fulfilling clinical criteria for APS. The mean time from the confirmation of the presence of aPL to the diagnosis of APS was 73±61.5 months. Patients with thrombocytopenia had higher number of thrombosis compared with patients with normal platelet count (29.4% vs 6.6%, OR 5.9; 95%CI 1.7–20.9; p=0.003).
Conclusions a) In our series, the incidence of thrombocytopenia in patients with positive antiphospholipid antibodies that do not meet clinical criteria for APS is 12%. APL-positive patients who develop thrombocytopenia have a potential risk of developing APS in the future. b) Tobacco use could be a risk factor for the development of thrombocytopenia in this population. c) Autoantibodies load is a risk factor for the development of thrombocytopenia.
Disclosure of Interest None declared