25
Table 15. World Health Organization Diagnostic Criteria for
Cutaneous and Systemic Mastocytosis
Cutaneous
mastocytosis
Typical clinical findings of urticaria pigmentosa or maculopapular
cutaneous mastocytosis, diffuse cutaneous mastocytosis, or solitary
mastocytoma and typical infiltrates of mast cells in a multifocal or
diffuse pattern at skin biopsy examination
Systemic
mastocytosis
Diagnosis of systemic mastocytosis is made if 1 major criterion and 1
minor criterion are present or if 3 minor criteria are met
Major criterion Multifocal, dense infiltrates of mast cells (≥15 in aggregates)
detected in sections of bone marrow and/or another extracutaneous
organ and confirmed by tryptase immunohistochemistry or other
special stains
Minor criteria
A In biopsy sections of bone marrow or other extracutaneous organs,
>25% of mast cells in the infiltrate are spindle-shaped or have
atypical morpholog y; or, of all mast cells in bone marrow aspirates
smears, >25% are immature or atypical mast cells
B Detection of activating point mutation at codon 816 of KIT in bone
marrow, blood, or another extracutaneous organ
C Mast cells in bone marrow, blood, or another extracutaneous organ
express CD117 with CD2 and/or CD25
D Serum total tryptase persistently >20 ng/mL in the absence of
associated clonal myeloid disorder
