Possible mechanisms of fibrin deposition in the hypereosinophilic syndrome.

Patients with the hypereosinophilic syndrome (HES) are at increased risk of thrombosis and have signs of fibrin deposition in the myocardial cavity; the pathogenesis of these complications is still unknown. We have studied a 51-year-old man affected by HES with heart, lung, skin, and gastrointestinal involvement. Routine laboratory parameters of the hemostatic system were normal with the exception of blood fibrinolytic activity. The latter was evaluated by both diluted blood clot lysis time and euglobulin lytic activity on fibrin plates before and after 10 min venous occlusion. The fibrinolytic activity measured on four occasions during a 3-month period, was impaired both in basal conditions and following venous occlusion. Platelet studies on two different occasions before and during therapy showed spontaneous platelet aggregation, lowered threshold concentrations of various aggregating agents, reduced platelet regeneration time and increased plasma beta-thromboglobulin concentration. The patient's polymorphonuclear cells (more than 75% eosinophils) were devoid of any procoagulant activity (PCA). Instead, patient's mononuclear cells studied before therapy generated significantly higher PCA on stimulation by endotoxin than cells from control subjects. The procoagulant response to endotoxin decreased markedly during therapy. The observed abnormalities could, at least partially, contribute to fibrin deposition in HES.