Platelets–Leucocyte Satellitism: Love Is in the EDTA!

In what may be called the roller-coaster ride profession of pathologists, there are many landscapes passing by that we see but do not look at! However, once in a while, a rare sighting forces us to pull the breaks. Platelet satellitism is one such uncommon, peculiar phenomenon that shows platelets rosetting around neutrophils and sometimes monocytes.^[1,2] Exposure of a cryptic antigen on the platelets treated with ethylenediaminetetraacetic acid (EDTA) may be responsible for this phenomenon, giving a spurious thrombocytopenic picture on a complete blood count.^[3]

We came across this alluring finding recently in the peripheral blood smear of a 16-year-old patient of BCR-ABL-positive acute lymphoblastic leukemia (ALL), who was in remission.

Approximately 60% of neutrophils showed at least four or more platelets sticking to their surface (►Fig. 1). Occasional monocytes were also seen covered with platelets.

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Fig. 1

Leishman stained peripheral blood smear of the patient with neutrophils surrounded by platelets (100x oil immersion).

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Platelet satellitism is a rare cause of spurious thrombocytopenia. On PubMed search, we could find only 72 articles in the English language on the subject, of which only 3 were from India.

The postulated mechanism for this picturesque phenomenon is the presence of IgG autoantibodies in the patient's serum, directed against a cryptic domain of the αIIbβ3 integrin of platelets, that is unmasked in the presence of EDTA. The Fcγ receptor (CD16) of neutrophils or monocytes react to this autoantibody causing rosetting. The reason for the presence of such autoantibodies in some individuals is still obscure.^[3,4]

Platelet satellitism has been described in texts,^[5,6] to be seen usually in healthy individuals. It has also been reported in diseases such as lymphoma^[7] and autoimmune hemolytic anemia.^[8]

Apart from pseudo-thrombocytopenia, platelet satellitism does not have profound clinical implications. However, a distinctive morphology with platelets apparently defying the laws of entropy, arranging themselves in an orderly manner, around polymorphs, is rare and should not be missed.