F5 and essential thrombocythemia: Many causes have been described [2,4]; a prothrombotic haematologic disorder (antiphospholipid antibody syndrome, homocysteinuria, Factor V Leiden, protein C deficiency, paroxysmal nocturnal haemoglobinuria, essential thrombocythaemia, thrombrotic thrombocytopenic purpura), vasculitic disorders, sepsis (meningo-encephalitis, mastoiditis), trauma, severe dehydration, and certain drugs.