= MYELOSCLEROSIS = AGNOGENIC MYELOID METAPLASIA = MYELO-PROLIFERATIVE SYNDROME = PSEUDOLEUKEMIA

= hematologic disorder of unknown etiology with gradual replacement of bone marrow elements by fibrotic tissue

Characterized by:

1. extramedullary hematopoiesis
2. progressive splenomegaly
3. anemia
4. variable changes in number of granulocytes + platelets; often predated by polycythemia vera

Cause:

1. primary: rare in children
2. secondary: radiation therapy / chemotherapy for leukemia or lymphoma or metastatic disease; Gaucher disease

Age: usually >50 years

Path: fibrous / bony replacement of bone marrow; extramedullary hematopoiesis

Associated with: metastatic carcinoma, chemical poisoning, chronic infection (TB), acute myelogenous leukemia, polycythemia vera, McCune-Albright syndrome, histiocytosis

• dyspnea, weakness, fatigue, weight loss, hemorrhage
• normochromic normocytic anemia; polycythemia may precede myelosclerosis in 59%
• dry marrow aspirate

Location: red-marrow–containing bones in 40% (thoracic cage, pelvis, femora, humeral shafts, lumbar spine, skull, peripheral bones)

• hepatosplenomegaly ← hematologic proliferation
• widespread diffuse increase in bone density (ground-glass sclerosis) predominantly affecting medullary cavity:
  • “jail-bar” ribs
  • sandwich / rugger jersey spine
• generalized increase in bone density in skull + obliteration of diploic space; scattered small rounded radiolucent lesions; or combination of both

MR:

• hypointense marrow on T1WI + T2WI
• signal intensity slightly higher than muscle on STIR

NUC:

• diffuse increased uptake of bone tracer in affected skeleton, possibly “superscan”
• increased uptake at ends of long bones

DDx:

1. With splenomegaly: chronic leukemia, lymphoma, mastocytosis
2. Without splenomegaly: osteoblastic metastases, fluorine poisoning, osteopetrosis, chronic renal disease