Primary myelofibrosis

1.5 per 100000, M=F, 50-60 years
Myeloproliferative neoplasm of unknown etiology
Clonal proliferation of hematopoietic stem cells
Progressive bone marrow fibrosis leads to anemia, splenomegaly and extramedullary hematopoiesis
JAK2 genetic abnormality in 55% cases
Pancytopenia with abnormal red cell morphology
Weakness, dyspnea, weight loss
Increased risk of infection and gout
Sites of extramedullary hematopoiesis: liver, spleen, lymph nodes, lung, choroid plexus, kidney
Death in 2-3 years if allogenic stem cell transplant is not done. Leukemia may also develop

Bone sclerosis – diffuse, patchy, mainly in axial skeleton and in major long bone metaphyses
Sclerosis – due to trabecular and endosteal new bone formation, this reduces marrow diameter
Lucent areas in bone due to fibrous tissue
Periosteal reaction – 1/3 of cases – at medial aspect of distal femur and proximal tibia
Mixed sclerotic and lytic pattern – ‘superscan’ appearance
MRI shows synovium infiltration by bone marrow elements
Leukemic conversion shows extraosseous soft tissue mass
Extramedullary hematopoiesis – hepatosplenomegaly, bilateral paravertebral masses in thorax, enlargement of ribs, pre-sacral mass. Fat containing non calcifying lesions. Fat signal suggests inactivity. Enhancement suggests activity