[Essential thrombocythemia: a myeloproliferative state on the rise. Clinico-biological study and course of 44 cases].

Forty-four cases of essential thrombocytosis (ET) were diagnosed in the last 20 years, 19 males and 24 females (M/F: 0.76), aged between 3 and 86 years (median, 62 years), and 9 of them being under 40 years of age. The M/F ratio for patients under 60 years was 0.5, whereas it was 1.09 for patients over 60. The clinical forms at onset were: asymptomatic, 36.5%; as a bleeding disorder (BD), 20.4%; as thrombotic disease (TD) 22.7%; BD/TD, 13.6%, and others, 6.8%. The most important biological features included platelet count over 1.000 x 10(9)/L (59.1%), abnormal platelet aggregation, chiefly with ADR (56.5), mild reticulin myelofibrosis (55%), abnormal karyotype (2.6%), moderately high LDH levels (56.8%) and pseudo-hyperkalaemia (40%). The initial therapeutic approach was: observation (12 cases), antiaggregating agents (6 cases), and chemotherapy (BSF, HU, etc.) in the remainders. One patient evolved quickly into acute myelogenous leukaemia and two others suffered a late transformation into polycythaemia vera (PV) and myeloid metaplasia, respectively. The median survival was over 11 years, this being longer in patients under 60 years of age, in those with platelet count at diagnosis between 600 and 1000 x 10(9)/L and in those without initial symptoms of thrombosis. The advent of electronic blood-cell counters has made ET no longer a rare chronic myeloproliferative disease, its incidence coming now closer to that of PV; thus, in the last four quinquennial periods the incidence of ET/PV has evolved as following: 1/19, 4/16, 13/18 and 26/29.