Microparticles as a Predictor of Acute Deep Venous Thrombosis in a Patient with Antiphospholipid Antibody Syndrome.

Microparticles (MP) are cell membrane derived fragments released as a result of apoptosis or cellular activation that may be prothrombotic. Elevated numbers of microparticles may circulate in inflammatory and thrombophilic disorders. Here, we report a patient with Antiphospholipid Antibody Syndrome (APS) in whom increased levels of circulating microparticles preceded the onset of clinically-detectable deep venous thrombosis (DVT). The patient is a 36 year old Hispanic male with previously diagnosed APS (DRVVT ratio 2.6, ACA IgG > 120, and β₂GPI IgG >100, IgA 74) complicated by several DVTs and transient ischemic attacks (TIA). Due to thrombosis on warfarin and enoxaparin, he was maintained on chronic therapy with fondaparinux. Microparticle analysis on three separate occasions was performed as part of an ongoing study of MPs in patients with antiphospholipid antibodies (aPL). The first analysis was performed during routine follow-up when the patient was asymptomatic. The second analysis was performed when the patient presented with complaints of left lower extremity tightness. Physical exam was normal, and Doppler ultrasound of the left lower extremity revealed chronic venous changes but no evidence of acute thrombosis. The patient was followed with plans for serial ultrasound examination. However, two days after this visit, the patient presented with acute DVT, confirmed by venous ultrasound. He was treated with five days of intravenous unfractionated heparin followed by reinstitution of fondaparinux. The third MP analysis was performed two weeks after the diagnosis of DVT. Isolation of MP was performed using a modification of previously described methods [Dignat-George et al, Thromb Haemost 91:668, 2004]. Platelet free plasma (PFP) was labeled with monoclonal antibodies for CD 144 and CD 105 (against endothelial cell VE cadherin and endoglin, respectively), and CD 41 (against platelet integrin αIIb) and analyzed by flow cytometry the same day as collection. Results of these analyses, expressed as number of MP/ml of PFP, are listed below.

These results demonstrate normal levels of circulating MPs in this APS patient while asymptomatic. However, endothelial cell and platelet MPs increased 20–35 fold prior to the development of venous-ultrasound detectable DVT, and decreased following therapy. While previous reports have documented elevated levels of MP in the setting of established thrombosis, we believe that this is the first description of a serial analysis of microparticles in an APS patient during an asymptomatic period, during incipient thrombosis not otherwise clinically diagnosable, and after treatment of acute DVT. MPs may prove to be a sensitive marker of incipient DVT in patients with negative vascular ultrasound studies.