Paradoxical thrombosis part 1: factor replacement therapy, inherited clotting factor deficiencies and prolonged APTT

The pathogenesis of venous and arterial thrombosis is complex and multifaceted, entailing a multitude of risk factors, which only marginally overlap between the two vessels districts. Along with conventional and universally recognized risk factors, thrombosis might also develop as a consequence of unusual, atypical, unsuspected and even paradoxical conditions. Although the term "paradoxical embolism" is typically used to identify an embolization process that originates from the low-pressure venous system and may generate ischemic stroke or peripheral arterial occlusion through a cardiac or pulmonary shunt, there are additional clinical circumstances whereby the risk of thrombosis is surprising, unpredicted or even neglected. In this article we thereby analyze the prevalence, as well as the pathogenesis, of thrombosis associated with apparently paradoxical triggers such as during factor replacement therapy in haemophiliacs or in patients with von Willebrand disease; in patients with inherited clotting factor deficiencies especially involving factor XII, factor VII, fibrinogen; or in those with a prolonged activated partial thromboplastin time for the presence of lupus anticoagulant.