Page 223 - Essential Haematology

Chapter 15 Myeloproliferative neoplasms / 209

tion and overproduction of platelets. Th e haemat- Clinical and l aboratory fi ndings
ocrit is normal and the Philadelphia chromosome

The dominant clinical features are thrombosis and
or BCR - ABL1 rearrangement are absent. Th e bone
haemorrhage. Most cases are symptomless and diag-
marrow shows no collagen fibrosis. A persisting nosed on routine blood counts. Th rombosis may

9
platelet count of > 450 × 10 /L is the central
occur in the venous or arterial systems (Fig. 15.5 b)
diagnostic feature but other causes of a raised
whereas haemorrhage, as a result of abnormal plate-
platelet count (particularly iron defi ciency, infl am-
let function, may cause either chronic or acute
matory or malignant disorder and myelodysplasia)
bleeding. Some patients (JAK2 + ) present with
need to be fully excluded before the diagnosis can
Budd – Chiari syndrome when the platelet count
be made.
may be normal because of the splenomegaly. A char-
Half of patients show the JAK2 (Val617Phe)
acteristic symptom is erythromelalgia, a burning
mutation and these cases tend to resemble more
sensation felt in the hands or feet and promptly
closely PV with higher haemoglobin and white cell
relieved by aspirin. Up to 40% of patients will have
counts than JAK2 negative cases. Mutations within
palpable splenomegaly whereas in others there may
the MPL gene are seen in 4% of cases. Rare primary
be splenic atrophy because of infarction.
familial cases in children have been associated with
Abnormal large platelets and megakaryocyte
mutations in the genes for thrombopoietin or its
fragments may be seen on the blood fi lm (Fig.
receptor MPL.
15.8 ). The bone marrow is similar to that in PV but

an excess of abnormal megakaryocytes is typical.
Cytogenetics and molecular analysis are analysed
Diagnosis to exclude BCR - ABL1 + CML. Th e condition
This used to be based on the exclusion of other must be distinguished from other causes of a raised

causes of chronic thrombocytosis but now that spe- platelet count (Table 15.5 ). Platelet function tests

cific genetic lesions have been identified a positive (see p. 328 ) are consistently abnormal, failure of

diagnosis can be made in approximately 50% of aggregation with adrenaline being particularly
cases. characteristic.
Prognosis and t reatment
Suggested d iagnostic c riteria for The principle is to reduce the risk of thrombosis or

e ssential t hrombocythaemia haemorrhage which are the major clinical problems.
(From Beer P.A. and Green A.R. (2009)
Hematology Am Soc Hematol Educ Program ,
621 – 8.)
Diagnosis requires A1 – A3 or A1 + A3 – A5:
9
A1 Sustained platelet count > 450 × 10 /L.

A2 Presence of an acquired pathogenetic mutation

(e.g. in JAK2 or MPL ).
A3 No other myeloid malignancy, PV, primary

myelofibrosis, chronic myeloid leukaemia
(CML) or myelodysplastic syndrome.
A4 No reactive cause for thrombocytosis and
normal iron stores.
A5 Bone marrow trephine histology showing
increased megakaryocytes with prominent large Figure 15.8 Peripheral blood fi lm in essential

hyperlobulated forms; reticulin is generally not thrombocythaemia showing increased numbers of
increased. platelets and a nucleated megakaryocytic fragment.