[Severe thrombopenias during heparin therapy. A phenomenon of intra-vascular platelet aggregation]

Haemorrhage or thromboembolism during heparin therapy are usually attributed to a prescribing error. However, these clinical manifestations--especially thromboembolism--may occur with heparin therapy during severe thrombocytopenia. The authors describe the clinical, biological and physiopathological features characterising this thrombocytopenia with reference to 7 personal cases and a review of the literature. The incidence of heparin-induced thrombocytopenia varies between 0.5 and 1%. It seems to be more common (4%) during heparin therapy for thromboembolic disease. The thrombocytopenia appears 8 days after the onset of heparin therapy. It is characterised by the high incidence of thromboembolism (70% of cases) compared to haemorrhagic phenomena (10% of cases). Thrombocytopenia is asymptomatic in 20% of cases. The thrombocytopenia is peripheral, i.e. the bone marrow is normal, and isolated, i.e. there are no deficiencies in the factors of coagulation. One of our cases was of special interest because it was complicated by disseminated intravascular coagulation. Eight cases of disseminated intravascular coagulation have previously been reported. Analysis of platelet aggregation demonstrates the relationship between heparin and thrombocytopenia. Mixing the plasma of patients with thrombocytopenia and plasma rich in platelets in the presence of heparin lead to thrombo-agglutination. In contrast, in control and non-thrombocytopenic heparinised subjects, no reaction was found. These observations prove the existence of a platelet aggregant factor in the plasma during thrombocytopenia. This disappears 6 weeks to 2 months after stopping heparin. This platelet aggregant factor initiates platelet aggregation which is responsible for thrombocytopenia and for the initiation of phenomena of coagulation, so explaining the thromboembolic phenomena.(ABSTRACT TRUNCATED AT 250 WORDS)