Childhood essential thrombocythaemia without evidence of myeloproliferation: how many investigations should be done?

Abstract

Randi et al (2000) reported on a group of children who fulfilled the criteria of essential thrombocytosis (ET) and yet did not display the characteristics of myeloproliferation in adult ET. They suggested that these children might actually have ‘idiopathic thrombocytosis’ (IT). This disease entity is likely to be under-reported, as patients are often asymptomatic and are detected incidentally. We present a case that is quite similar to those reported by Randi et al (2000) . A 7-year-old Chinese girl was incidentally found to have thrombocytosis (platelet count 1256 × 109/l) while having investigations for primary nocturnal enuresis. When she was 3·5 years old, she was admitted for pneumonia, and her platelet count was 420 × 109/l at that time. Her parents' platelet counts were normal, and there was no family history of thrombocytosis. Her white cell count and differential count were unremarkable, and her platelet size was not enlarged. Haemoglobin, erythrocyte sedimentation rate and C-reactive protein were all within normal ranges. Neutrophil alkaline phosphatase score was low. Bone marrow examination showed an increase in megakaryocytes with normal maturation. There was a small increase in iron store with a few sideroblasts. Cytogenetics showed normal 46XX karyotype. No Bcr/Abl chimaeric transcript was demonstrated by reverse transcription polymerase chain reaction. Trephine biopsy revealed megakaryocytic hyperplasia with no myelofibrosis. Platelet function tests showed normal response to collagen and ritocetin, but reduced and reversible aggregation with ADP and absent response to adrenaline. She received a short course of low-dose aspirin and has been in good health for 4 years, with her platelet count ranging from 600 to 1414 × 109/l (mean > 1000 × 109/l). The platelet count has shown a trend of gradual fall over the past year. We believe our case is one of those with ‘IT’ and, in fact, she has remained asymptomatic for 4 years. It seems to me that the authors suggested that erythroid burst-forming unit (BFU-E) activity, erythropoietin (EPO), thrombopoietin (TPO) and intraplatelet 5-HT levels would be helpful in the diagnosis of childhood ET. We question whether there is any need to proceed with this set of tests in order to confirm the diagnosis of ET. How much additional help does this set of investigations offer compared with the guidelines recommended by the Polycythemia Vera Study Group ( Murphy, 1983; Michiels & Juvonen, 1997) or those from Dudley et al (1989) ? On the other hand, we would also like to know whether the BFU-E activity and EPO, TPO and intraplatelet 5-HT levels could have some predictive value for outcome. From this report, they do not seem to help in predicting the occurrence of any thromboembolic event, nor do they predict the progression to a myeloproliferative state. Myeloproliferation can occur as late as 11 years after the initial diagnosis has been reported ( Michiels & Van Genderen, 1997). In fact, Michiels & Van Genderen (1997) showed that all children with ET who subsequently progressed to myeloproliferative diseases or leukaemia had giant platelets with or without dysplastic megakaryocytes. Randi et al (2000) did not comment on the platelet size of their patients, which may actually have clinical significance. Simple morphological evaluation of platelet size may be more helpful than a lot of sophisticated tests in predicting the outcome of childhood ET/IT.