Thrombophagocytosis

An 81-year-old woman with pyelonephritis caused by Escherichia coli developed asymptomatic thrombocytopaenia (platelet count 71 000 µl⁻¹) on the third day of hospitalization. A peripheral blood smear revealed monocytes (Figure 1A) and neutrophils (Figure 1B–D) with platelets in their cytoplasm. In particular, thrombophagocytosis was observed in more than 50% of neutrophils. Laboratory workup for other causes of thrombocytopenia including disseminated intravascular coagulation was negative. The patient completed an uneventful course of antibiotic therapy. Thrombophagocytosis is a rare phenomenon. Only two cases of peripheral thrombophagocytosis have been reported previously: one in urosepsis caused by Citrobacter freundii [1] and the other one in B-cell lymphoma [2]. We are also aware of three reported cases of thrombophagocytosis in the bone marrow: two in haemophagocytic syndrome [3], [4] and one in juvenile dermatomyositis [5]. The binding of pathogens to platelets in septicaemia is thought to mediate thrombophagocytosis by neutrophils and monocytes.

Figure 1. Peripheral blood smear showing thrombophagocytosis in a patient with pyelonephritis: (A) monocytic and (B–D) neutrophilic thrombophagocytosis.