Antiphospholipid Antibodies and Platelet Activation as Thrombotic Risk Factors in Thrombocythemia Associated with Myeloproliferative Disorder

Abstract number: P0999

Bidot C, Jy W, Fontana V, Ahn E, Horstman L, Ahn Y

Introduction and method:  Thrombosis is a major morbidity in thrombocythemia (TC) associated with myeloproliferative disorder. To further define risk factors for thrombosis (TB), we investigated antiphospholipid antibodies (APLA) and status of activation of platelet and endothelial cells in 35 patients with this disorder. IgG and IgM APLA was measured by ELISA for 6 antigens: beta2GP1, cardiolipin (CL), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE), FVII/VIIa. Activation of platelets and endothelium were assayed with CD62P and endothelial microparticles (EMP) respectively. These measures were compared in 14 with and 21 patients without thrombotic complications.

Results:  At least one positive APLA was detected in 66% of all TC patients. The incidence was significantly higher in the TB group (92.0%) than non-TB group (47.6%, P < 0.05). Multiple APLA were more frequent in TB for both IgG and IgM, for all 6 antigens tested (P < 0.05). However, IgM APLA predominated, being about 2-fold more frequently positive than IgG for all 6 antigens. Platelet activation measured by CD62P was significantly higher in the TB than non-TB group (P < 0.05) but EMP did not differ between 2 groups. The most frequent thrombotic complication was ischemic cerebrovascular disease (ICVD), characterized by recurring TIA like syndromes with complete neurologic recovery but tendency to progress to cognitive impairment and dementia in long term follow-up. Reversible but recurring thrombosis were common features of TB in patients with TC.

Summary:  APLA is quite frequently detected (66%) in patients with TC. APLA and platelet activation appear risk factors for thrombosis. Recurring and reversible TIA and ICVD are most frequent thrombotic complications, some progressing to cognitive dysfunction and dementia. Activation of platelets but not of endothelium may explain reversible and recurrent features of thrombotic complications among patients with TC.