Platelet satellitism, spurious neutropenia, and cutaneous vasculitis: casual or causal association?

About 90 cases of platelet satellitism (PS) have been published, most of them involving neutrophils, a few comprising monocytes, and one case involving basophils. The case of a 30-year-old female patient with cutaneous vasculitis who developed asymptomatic severe neutropenia is reported. All blood smears (BS) prepared from peripheral blood samples collected with either ethylenediaminetetraacetic acid, trisodium citrate, and heparin showed PS involving neutrophils, eosinophils, and monocytes. Immunohistochemistry analysis of her skin biopsy and BS, employing peroxidase stain for the detection of antibodies directed against IgG, IgA, IgM, and C3, revealed an intense positive reaction only for IgG in the endothelium and leukocyte clumps within the microvasculature, as well as in peripheral blood neutrophils displaying the PS phenomenon. Transfer of the PS phenomenon was demonstrated by incubating the patient's plasma with leukocytes from an ABO-compatible healthy donor. In our patient, PS did not disappear after incubation at 37 degrees C, suggesting that this might be a different or "atypical" PS phenomenon probably mediated by an autoimmune process involving an IgG-class antibody responsible for both conditions, PS, and cutaneous vasculitis.