polycythaemia rubra vera

introduction

myeloproliferative disorder resulting in polycythaemia
~10 new cases per million population per year
incidences of polycythaemia vera, essential thrombocythaemia, and myelofibrosis were 10x higher among Ashkenazi Jews in northern Israel than in persons of Arabic descent in the region.
most cases occur in those 40-60 yrs old and are due to acquired (not inherited) mutations in genes such as JAK2, TET2
rarely, risk of PRV may be inherited in an autosomal dominant manner

FBE:
- raised haematocrit > 0.52 in men and > 0.48 in women
- raised RBC mass > 25% above normal
- neutrophis and basophils may be raised
- raised platelet count in 50% of patients
low ESR due to increase in zeta potential
JAK2 mutation is strongly associated
- those who are JAK2 negative may need bone marrow biopsy

there is no current curative Rx, but most patients have an almost normal life span with life-long treatment
low dose aspirin seems to halve the risk of thrombotic complications in those with no PH thrombotic events ¹⁾
asymptomatic patients aged < 40 years can be considered for therapeutic phlebotomies alone to maintain a hematocrit level of less than 45% although this Rx is being re-evaluated
other patients can undergo myelosuppressive therapy with hydroxyurea 500 mg PO twice per day (titrated to effect)
- appears to reduce stroke risk by a further 30%
- these patients may eventually develop myelofibrosis
Janus kinase inhibitors
- Ruxolitinib (Jakafi) 10 mg PO twice per day appears to be superior to hydroxyurea for disease control HOWEVER:
  - serious withdrawal symptoms make gradual dose reduction important
  - 82% developed anaemia, 67% thrombocytopenia and 15% neutropenia hence need to monitor FBE
radioactive phosphorous can be used as an alternative therapy in older patients

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