CALR-positive essential thrombocythaemia preceded by immune thrombocytopaenia

Abstract

Presentation: The patient initially presented with gum bleeding and a petechial rash. Diagnosis: The patient was found to be severely thrombocytopaenic and bone marrow biopsy showed a marked excess of megakaryocytes consistent with a diagnosis of immune thrombocytopaenia (ITP). She underwent splenectomy. Seven years following splenectomy, her platelet count began to rise again, and repeat bone marrow sampling revealed an increase in megakaryocytes with evidence of clustering. On further testing the calreticulin (CALR) exon 9 variant was found and a diagnosis of essential thrombocythaemia (ET) was made. Treatment: Thromboprophylaxis and cytoreductive therapy (hydroxyurea) were initiated following ET diagnosis. Discussion: Possible mechanisms of ET (platelet excess) following ITP (platelet deficiency) include the known associations of autoimmune conditions and malignancy and the effects of immunosuppression and splenectomy in tumorigenesis. To our knowledge, this is the first recorded case of ITP preceding later development of CALR- positive ET