mastocytosis


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  • Clinical

    • cutaneous mastocytosis more common in children
    • site: skin (80%), marrow (always in systemic)
    • cutaneous: urticaria, pigmentation
    • systemic: systemic symptoms, eosinophilia, anemia, neutropenia, thrombocytopenia

  • Criteria

    • cutaneous
      • characteristic skin lesion
      • mast cell infiltrate
      • rule out systemic mastocytosis
    • systemic (1 major + 1 minor, or 3 minors)
      • major: extracutaneous mast cell infiltrate (15 cell aggregates)
      • minor
        • atypical, spindle, immature (aspirate) mast cells in > 25% of biopsy
        • KIT activating mutation at codon 816
        • aberrant CD2 or CD25 expression of mast cells
        • serum tryptase > 20 ng/mL in the absence of another clonal myeloid disorder
    • B-findings: for smouldering mastocytosis
      • > 30% mast cells in marrow or serum tryptase > 200 ng/mL
      • mild non-mast cell lineage dysplasia or proliferation
      • organomegaly (but no liver failure or hypersplenism) or lymphadenopathy
    • C-findings: for aggressive mastocytosis
      • marrow dysfunction (ANC < 1, Hb < 10, plt < 100)
      • hepatomegaly with liver failure, ascites or portal hypertension
      • splenomegaly with hypersplenism
      • osteolytic lesions or pathological fractures
      • wt loss from GI mast cell infiltrates causing malabsorption

  • Types

    • cutaneous mastocytosis
      • urticaria pigmentosa / maculopapular cutaneous mastocytosis (UP/MPCM): most common
      • diffuse cutaneous mastocytosis: diffuse, non-focal, peau d'orange, exclusively in children
      • solitary mastocytoma of skin: single lesion, in infants
    • systemic mastocytosis
      • indolent systemic mastocytosis: lack C-findings
        • bone marrow mastocytosis: lack skin lesions
        • smouldering systemic mastocytosis: 2 B-findings
      • systemic mastocytosis with AHNMD: also has MDS, MPN, AML, lymphoma or other heme neoplasm
      • aggressive systemic mastocytosis: has C-findings
        • lymphadenopathic mastocytosis with eosinophilia
      • mast cell leukemia: mast cells (10% blood, 20% aspirate)
    • mast cell sarcoma: unifocal, high grade tumor
    • extracutaneous mastocytoma: unifocal, low grade tumor

  • Stains

    • positive: tryptase/chymase, CD117, CD2, CD25, CAE
    • negative: MPO

  • Molecular

    • KIT codon 816 activating mutation (D816V)

  • Ddx

    • mast cell hyperplasia
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