Myeloproliferative Disorders

See CML, Presentation: Polycythaemia, and Presentation: Thrombocytosis/Thrombocytopenia for the individual conditions this classification covers.

Disorders of clonal proliferation of haematopoietic stem cells, causing excessive production of a cell line — generally without dysplastic cells or loss of production of normal cell lines. Course and prognosis vary considerably, but all have the capacity to progress to bone marrow fibrosis (and thus ineffective production of other cell lines) or acute leukaemia.

Classification

More common conditions:

• Chronic myelogenous leukaemia (CML) — BCR-ABL positive.
• Polycythaemia vera (PV).
• Essential thrombocythaemia (ET).
• Primary myelofibrosis (PMF).
• Myeloproliferative neoplasms, unclassifiable.

Less common conditions: chronic neutrophilic leukaemia; chronic eosinophilic leukaemia.

Myelodysplastic/myeloproliferative neoplasms with features of both: chronic myelomonocytic leukaemia (CMML); atypical CML (aCML, BCR-ABL negative); juvenile myelomonocytic leukaemia (JMML); MDS/MPN with ring sideroblasts and thrombocytosis (MDS/MPN-RS-R); unclassifiable MDS/MPN.

Mastocytosis was previously grouped here but is now its own category, given its distinctive clinical features.

Clinical presentation

Uncommon — usually asymptomatic and picked up on routine FBCs. May have constitutional symptoms (fevers, weight loss). Splenomegaly is common in CML and primary myelofibrosis, but not much else in this group. Thrombosis at unusual sites should prompt investigation for a myeloproliferative neoplasm.

JAK inhibitors (ruxolitinib, and newer momelotinib for myelofibrosis with anaemia) are established targeted therapies for myelofibrosis symptom control.