Proliferation of haemopoeitic stem cells with bone marrow fibrosis. Fibrosis is caused by release of growth factors by abnormal megakaryocytes which stimulate fibroblasts.

Most are idiopathic but can be secondary to Polycythaemia Vera, Essential Thrombocytosis, chemotherapy, radiotherapy, myelodysplasia, carcinoma

20% asymptomatic at diagnosis, majority have splenomegaly, hepatomegaly, gout, portal hypertension and ascites

Bloods: FBC - normochromic normocytic anaemia. JAK-2 mutation often positive

Blood film: Teardrop poikilocyte and giant platelets

Bone Marrow Aspirate: often unsuccessful - ‘dry tap’

Conservative: Watch and wait if asymptomatic

Medical: Blood product support, radiotherapy, thalidomide, corticosteroids

Allogeneic stem cell transplant.

Surgical: Splenectomy if spleen painful or massive

Poor, median survival 3-5 years

Haemorrhage, transformation to AML, infection, thrombosis, progressive cachexia