Clonal haematological malignancy characterised by pronounced symptoms, along with an increased risk of thrombosis and the potential for evolution to myelofibrosis and secondary acute myeloid leukemia
Aetiology
Median age of diagnosis ~65 but can affect younger patients
JAK2 - kinase mutation present in over 95% of PV patients
Pathophysiology
JAK2 mutation (substitution) results in loss of autoinhibition → activation of erythropoiesis in the absence of ligand
Clinical features
Asymptomatic - may be discovered on routine blood count in a person with no related symptoms or there may be nonspecific complaints of lethargy and tiredness
Marrow failure - fibrosis or leukaemic transformation (transformation risk is low)
Thrombosis - arterial or venous including TIA, MI, abdominal vessel thrombosis, claudication, erythromelalgia
Headache, fatigue
Itch - aquagenic pruritus (worse after a hot shower or bath)
Investigations
Bloods:
FBC, blood film - high haemoglobin/haematocrit accompanied by erythrocytosis (a true increase in red cell mass) but can have excessive production of other lineages
JAK2 mutation status
If JAK2 negative but high clinical suspicion - erythropoietin levels, bone marrow biopsy
Investigation for secondary/pseudocauses - CXR, O2 saturation/ABGs, drug history
Secondary polycythaemia - chronic hypoxia, erythropoietin-secreting tumour etc.
Pseudopolycythaemia e.g. dehydration, diuretic therapy, obesity)