Monitoring

Long-term monitoring of this disorder commonly requires the direction and supervision of an experienced haematologist.

Blood counts are monitored on a regular basis to review control. Patients receiving cytoreductive therapy require blood count monitoring every 1 to 2 weeks at treatment initiation until stable, then as clinically indicated. Complications and adverse effects of therapy are monitored at the same time.

Response criteria have been established for treatment.[99] Complete response is defined as:

  • Durable (lasting at least 12 weeks) resolution of disease-related signs including palpable hepatosplenomegaly, large symptom improvement (≥10-point decrease in myeloproliferative neoplasm symptom assessment form total symptom score),[100] and

  • Durable (lasting at least 12 weeks) peripheral blood count remission, defined as haematocrit <45% without phlebotomies, platelet count ≤400 × 10⁹/L (400 × 10³/microlitre or 400,000/microlitre), and white blood cell count <10 × 10⁹/L (10 × 10³/microlitre or 10,000/microlitre), and

  • Without progressive disease, and absence of any haemorrhagic or thrombotic event, and

  • Bone marrow histological remission, defined as the presence of age-adjusted normocellularity and disappearance of trilinear hyperplasia, and absence of grade >1 reticulin fibrosis.

Fulfilment of the first three criteria above without bone marrow histological remission, defined as the persistence of trilineage hyperplasia, constitutes a partial remission.

Progression to post-PV myelofibrosis is defined as:[101]

  • Required criteria:

    • Documentation of a previous diagnosis of PV as defined by the World Health Organization criteria

    • Bone marrow fibrosis grade 2-3 (on 0-3 scale) or grade 3-4 (on 0-4 scale).[102][103]

  • Additional criteria (two are required):

    • Anaemia or sustained loss of requirement of either phlebotomy (in the absence of cytoreductive therapy) or cytoreductive treatment for erythrocytosis

    • A leukoerythroblastic peripheral blood picture

    • Increasing splenomegaly, defined as either an increase in palpable splenomegaly of ≥5 cm (distance of the tip of the spleen from the left costal margin) or the appearance of a newly palpable splenomegaly

    • Development of ≥1 of 3 constitutional symptoms: >10% weight loss in 6 months, night sweats, unexplained fever (>37.5°C).

Risk assessment is an ongoing process, and development of high-risk features requires more intensive therapy.

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