Trends in the incidence of chronic Philadelphia chromosome negative (Ph-) myeloproliferative disorders in the city of Goteborg, Sweden, during 1983-99

Objective. In the literature the incidence rates for the chronic Philadelphia chromosome negative (Ph-) myeloproliferative disorders (MPD) are known to vary extensively; only a few studies have, however, been concerned with incidence trends over time. Therefore, the aim of the present work was to investigate possible trends as regards incidence rates over time for Ph-MPD. Design. Herein, we carried out a retrospective population-based survey on the incidence of polycythaemia vera (PV), essential thrombocythae-mia (ET) and chronic idiopathic myelofibrosis (IMF), in the city of Goteborg (Sweden), covering the years 1983-99. Results. The study comprised 416 patients with Ph-MPD. There were 205 patients with PV, 153 patients with ET, 34 with IMF and 24 with unclassified MPD. The annual incidence for PV was 1.97 per 10(5) inhabitants; the corresponding figures for ET and IMF were 1.55 per 10(5) and 0.30 per 10(5) inhabitants, respectively. There was a significant increase in the annual incidence rate for ET (P = 0.008); this increase was significant for male subjects (P = 0.015) but did not reach significance for females (P = 0.118). No such increase over time was recorded as regards PV and IMF. Conclusions. The increasing annual incidence rate for ET is most possibly explained by the more frequent use of automated platelet counts whenever a patient consults a doctor. Thereby, an increasing number of patients with overt thrombocytosis of unknown origin are discovered and will be referred to specialists within the field of haematology for a correct diagnosis.