Page 261 - Haematologica Atlas of Hematologic Cytology

CHAPTER 32 - Immune thrombocytopenia
Chapter 32. IMMUNE THROMBOCYTOPENIA
Immune thrombocytopenia (ITP) is the most frequent cause of isolated thrombocytopenia. This disorder was previously known as idiopathic thrombocytopenic purpura, but its autoimmune origin, and the observation that the majority of patients have no purpura, induced the International Working Group on Immune Thrombocytope- nia to propose changing its name to immune thrombocytopenia (Rodeghiero et al., 2009).
The diagnosis of ITP still remains one of exclusion, and cytological evaluation of blood and bone marrow films does not identify any diagnostic feature. However, evaluation of blood film is an important tool in distinguishing ITP from inherited thrombocytopenias, which often have characteristic abnormalities of blood cells that direct the physician to the right diagnosis (See Chapter ‘Inherited thrombocytopenias’). Thus, careful examination of blood smears is recommended whenever the possibility that a thrombocytopenic patient has had a low platelet count since birth cannot be excluded. In fact, a large proportion of patients with inherited thrombocytopenias are misdiagnosed with ITP and receive treatments that are not only useless but actually dangerous (Balduini et al., 2013).
Blood film evaluation is also useful as a diagnostic procedure when there is suspicion of more complex hema- tologic disorders that may initially present with thrombocytopenia as the most evident defect (acute leukemias, myelodysplastic syndromes and thrombotic microangiopathies). Finally, examination of films prepared with anti- coagulated blood may identify the platelet clumps that are typical of EDTA-dependent pseudothrombocytopenia (see Capther 1). Consideration of this hypothesis is particularly important when diagnosing subjects with appa- rently severe thrombocytopenia but no bleeding diathesis.
Bone marrow examination is only rarely required as part of the diagnostic procedure for ITP (Provan et al., 2010). It has been suggested that it should be reserved for patients who are over 60 years of age to exclude myelodysplastic syndromes, particularly those forms with monolineage involvement. Moreover, it has been re- commended for patients with atypical features or those who have had a poor response to treatment or for whom splenectomy is being considered.
The figures in this chapter show the cytological characteristics of blood and bone marrow of ITP patients. As already discussed, there are no diagnostic features, and the picture is that common to all forms of throm- bocytopenia with accelerated platelet turnover. A notable exception is represented by the few patients in whom antibodies not only shorten platelet survival but also affect megakaryocytes. In these cases, the abundance of megakaryocytes typical of ITP is absent and the number of these cells may even be reduced.
References
Rodeghiero F, Stasi R, Gernsheimer T, et al. Standardiza on of terminology, de ni ons and outcome criteria in im- mune thrombocytopenic purpura of adults and children: report from an interna onal working group. Blood. 2009;113(11):2386-2393.
Provan D, Stasi R, Newland AC, et al. Interna onal consensus report on the inves ga on and management of primary immune thrombocytopenia. Blood. 2010;115(2):168-186.
Noris P, Biino G, Pecci A, et al. Platelet diameters in inherited thrombocytopenias: analysis of 376 pa ents with all known disorders. Blood. 2014;124(6):e4-e10.
Balduini CL, Savoia A, Seri M. Inherited thrombocytopenias frequently diagnosed in adults. J Thromb Haemost. 2013;11(6):1006-1019.
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