Mk. Jensen et al., Incidence, clinical features and outcome of essential thrombocythaemia in a well defined geographical area, EUR J HAEMA, 65(2), 2000, pp. 132-139
In an attempt to characterise the clinical features, incidence and outcome
of essential thrombocythaemia (ET) we report our experience in a large unse
lected series of patients from a well defined region. All new cases of ET i
n the County of Copenhagen were registered during the period 1977-98. We id
entified 96 cases of ET, yielding an age- and sex-adjusted annual incidence
rate of 0.59/100.000 and a point-prevalence at last follow up of 11/100.00
0. The overall incidence rate was 0.31 and 1.00 per 100.000 population duri
ng the consecutive periods 1977-89 and 1990-98, respectively, corresponding
to a 3.2-fold increase. Median age at diagnosis was 67 yr (females 68 yr,
males 66 yr, range 18-87 yr), and the female to male (F/M) ratio was 2.6:1.
At diagnosis, 52% of the patients displayed no ET-related symptoms and wer
e discovered fortuitously by a routine platelet count. Forty-eight percent
presented with thrombohaemorrhagic phenomena, of which microvascular distur
bances of the central nervous system (CNS), extremities and skin were most
frequently observed (23%). Compared to patients diagnosed after 1989, patie
nts diagnosed before 1990 had a significantly higher mean platelet count, w
hite blood cell (WBC) count, lactate dehydrogenase (LDH) value and alkaline
phosphatase value. With a median follow up of 70 months, 5-yr survival was
76%, significantly lower than the expected survival of an age- and sex-mat
ched control group (p = 0.0052). Thirty-seven patients experienced a total
of 55 thrombohaemorrhagic events during follow-up, corresponding to an inci
dence of thrombosis and microvascular disturbances or haemorrhage of 8.1% p
er pt-yr and 2.5% per pt-yr, respectively. The number of patients experienc
ing thrombosis or microvascular disturbances was significantly higher among
the 29 patients who never received acetylsalicylic acid (ASA) compared to
the 67 patients who received ASA during follow up (45% vs. 21%; p = 0.017).
This study provides population-based data suggesting the benefit of treatm
ent with low-dose ASA in a non-selected population of patients with ET.