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974 Part VII: Neutrophils, Eosinophils, Basophils, and Mast Cells Chapter 63: Basophils, Mast Cells, and Related Disorders 975

A B

C D
Figure 63–3. Marrow sections. Marrow biopsy from an adult with indolent systemic mastocytosis showing characteristic focal aggregates of mast
cells, some of which are spindle-shaped, with admixed eosinophils and numerous small lymphocytes; different areas of the specimen were stained
by hematoxylin and eosin (H&E) (A, B; ×40 and ×200, respectively) or with an antibody to human CD117 (C; ×200) or tryptase (D; ×200). Areas that
contain many mast cells are depicted with arrows in A.

TABLE 63–6. Diagnostic Criteria for Systemic Mastocytosis Marrow involvement is much less common in children. In a
Major Criterion study of 17 children with cutaneous or disseminated mast cell dis-
ease, small focal mast cell lesions were observed in marrow biopsies
Multifocal, dense infiltrates of mast cells (≥15 mast cells in in 10 individuals, and increased mast cells in marrow aspirate films
an aggregate) detected in sections of marrow and/or other were noted in 5. The focal lesions found in children usually are
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extracutaneous organ(s) small and perivascular.
Minor Criteria Progression of marrow involvement in systemic mast cell disease
a. In biopsy sections of marrow or other extracutaneous organs, is variable. Some adults with indolent disease appear to have stable, or
>25% of the mast cells in the infiltrate are spindle shaped or even decreasing, marrow involvement over time. In contrast, a pro-
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have atypical morphology, or, of all mast cells in marrow aspi- gressive increase in focal mast cell lesions is more commonly observed
rate smears, >25% are immature or atypical mast cells in patients with more aggressive patterns of disease.
b. Detection of a point mutation in KIT at codon 816 in marrow,
blood, or other extracutaneous organ
c. Mast cells in marrow, blood, or other extracutaneous organs CLINICAL PRESENTATION
that coexpress CD117 with CD2 and/or CD25 Even though individuals may differ in the specific pathogenesis of their
d. Serum total tryptase persistently >20 ng/mL (if there is an asso- disease, all patients within a given category of mastocytosis (see Table
ciated myeloid disorder, this criterion is not valid) 63–5) tend to exhibit similar clinical features. Manifestations of the
The diagnosis of systemic mastocytosis can be made if one disease largely reflect the local and systemic consequences of mediator
major and one minor criterion are present or if three minor release from tissue mast cells. Effects caused by disruption of normal
criteria are met.
structures by local collections of mast cells also may be seen.

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