RESUMEN
A morphometric and immunohistochemical study was performed on trephine biopsies of the bone marrow in patients showing idiopathic thrombocytopenic purpura (ITP) and reactive thrombocytosis (RTH). Features of megakaryocytopoiesis were determined not only by using the periodic acid Schiff reaction (PAS), but also by immunostaining with the monoclonal antibody Y2/51, detecting a formalin-resistant epitope of glycoprotein IIIa (CD61). An increased number of megakaryocytes was observed in both ITP and in RTH as compared with a control group. Immunostaining revealed a predominance of small immature elements of this cell lineage, particularly in cases of ITP. Following previous experimental cell culture studies on megakaryocyte precursors and features derived from corresponding smear preparations, we characterized promegakaryoblasts immunomorphometrically. According to these calculations, ITP, as opposed to RTH, features a disproportionate expansion of the megakaryocyte precursor pool.