Diagnosis of essential thrombocythemia at platelet counts between 400 and 600x10(9)/L

Background and Objectives, Diagnostic criteria for essential thrombocythemi a (ET) remain essentially negative, that is, exclusion of other myeloprolif erative diseases and causes of reactive thrombocytosis, A platelet count ab ove 600x10(9)/L is still generally considered an absolute diagnostic criter ion although new protocols for positive diagnostic criteria have recently b een proposed, reducing the stringency of a definite platelet limit. This st udy demonstrates that a platelet count less than or equal to 600x10(9)/L is not a reliable diagnostic criterion for ET, especially In the early stages . Design and Methods. An ongoing retrospective study by the GIMMC analyzed 2, 316 ET patients diagnosed diagnosed according to the PVSG criteria, 68 had a platelet count less than or equal to 600x10(9)/L and were analyzed separa tely; 37 out of 68 were excluded from this analysis because of a follow-up shorter than 2 years and/or because of treatment with myelosuppressive agen ts. The remaining 31 patients were the subjects of our study. Results. After a median follow-up of 4.56 years (range 2-9.6 years) none of the 31 patients had a spontaneous decrease of platelets to the normal rang e. Transformation to a different chronic myeloproliferative disorders was n ever observed and no patient developed a condition known to produce reactiv e thrombocytosis, During follow-up, 23 patients (74%) were treated with ant i-aggregating drugs, mainly aspirin. The disease did not evolve Into acute in any patient, 1 had a thrombotic event presented hemorrhagic episodes. Me dian platelet count during follow-up was 534x10(9)/L (range 398-997x10(9)/L ). Interpretation and Conclusions. Long term follow-up has documented that our 31 patients were correctly diagnosed as having ET, although platelet count was less than or equal to 600x10(9)/L. Our patients were probably in a ear ly phase of their disease and following updated PVSG criteria would have be en misdiagnosed leading to Incomplete recognition of the natural history of the disease. Further, because an early diagnosis could also have a clinica l relevance, our results outline the need for new criteria for the diagnosi s of FT, The exclusion of patients with a platelet count between 400 and 60 0x10(9)/L may prevent patients, nevertheless at risk of vascular complicati ons, from being treated. (C) 2000, Ferrata Storti Foundation.