PB1355 - Long vaccine-induced immune thrombotic thrombocytopenia: a case report

Background: Vaccine-induced immune thrombotic thrombocytopenia (VITT) has been described following adenovirus vector-based COVID-19 vaccines. This condition is associated with important morbidity and mortality following thrombosis related complications. Diagnosis is confirmed based on results of platelet factor 4 ELISA detecting anti-PF4 antibodies and of platelet-activation assay. Initial treatment strategy has been established but long-term management and follow up remain unclear. Most platelet-activation tests become negative after 12 weeks.

Aims: Persistence of platelet-activating anti-PF4 antibodies has been observed in cases described as long VITT. This condition is challenging and needs to be defined.

Methods: We describe a case of VITT which can now be characterized as long VITT.

Results: The patient initially had a lower limb ischemia, pulmonary embolism and cerebral vein thrombosis. He was treated with prednisone, IVIG, argatroban and had a lower limb revascularization surgery. Rivaroxaban was then initiated for the acute treatment and continued for the secondary prevention of recurrent events. The patient still demonstrates positive platelet-activation tests and thrombocytopenia after more than 18 months of follow-up. No recurrent thrombosis or bleeding event have occurred and no IVIG were needed beyond initial hospitalization. He is not known for any relevant past medical history other than alcohol consumption and slight thrombocytopenia (130 x 10^9/L since 2015). It is unclear if the ongoing and more important thrombocytopenia could be explained by the persistent platelet-activating anti-PF4 antibodies or the patient’s habits.

Conclusion(s): Managing long VITT is challenging considering uncertainty regarding risks and benefits of long-term anticoagulation and potential needs of additional treatment. Additional data is needed to offer optimal long-term management for this patient population. We suggest that long VITT diagnosis definition might include the persistence within patient serum/plasma of anti-PF4 platelet-activating antibodies with clinical manifestations (e.g., thrombocytopenia) for more than 3 months.