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Chapter 149. Mastocytosis

Michael D. Tharp

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Mastocytosis at a Glance
  • The hallmark of mastocytosis is a pathologic accumulation of mast cells in tissues.
  • Mastocytosis occurs at any age.
  • The skin is the most commonly involved organ system.
  • Cutaneous findings consist of hyperpigmented macules, papules or nodules, or a diffuse infiltration of the dermis.
  • Generally benign in children.
  • In adults, most commonly associated with a somatic activating mutation of c-kit (codons 816 and 560).
  • Cutaneous manifestations may occur alone or in association with systemic disease.
  • Related features may be flushing, pruritus, hypotension, nausea, dyspepsia, and diarrhea.
  • Most common extracutaneous tissues involved are the bone marrow, liver, spleen, and lymph nodes.
  • May be associated with myeloproliferative and myelodysplastic disorders.
  • Classification of mastocytosis is critical for prognosis and treatment.
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Mast Cells at a Glance
  • Mast cells are derived from pluripotent stem cells.
  • Stem cell factor is required for proliferation and survival.
  • Mast cells release both pre-formed and generated mediators when activated.

Mastocytosis represents a group of disorders characterized by an abnormal accumulation of mast cells in one or more organs. While the true incidence of this disease is unknown, most cases are in children, with 60%–80% presenting within the first year of life. Congenital mastocytosis is less common, representing approximately 18%–31% of childhood cases.1,2 Adult-onset mastocytosis also occurs and is being more commonly recognized with newly established World Health Organization (WHO) criteria for this disease3 (Tables 149-1 and 149-2). This disorder has no gender preference, and it has been reported in all races.4 While most patients with mastocytosis have no family history, there are reports of familial cases, including monozygotic twins, some of which were discordant for this disease.4–6

Table 149-1 World Health Organization Classification of Mastocytosisa
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Table 149-1 World Health Organization Classification of Mastocytosisa

Variant Term

Abbreviation

Subvariants

Examples

Cutaneous mastocytosis

CM

Telangiectasia macularis eruptiva perstans (TMEP)

Urticaria pigmentosa

Diffuse CM

Mastocytoma of skin

Indolent systemic mastocytosis

ISM

Smoldering SM

Isolated bone marrow mastocytosis

SM-acute myelogenous leukemia

SM-myelodysplastic syndrome

SM-myeloproliferative disease

SM-chronic myelomonocytic leukemia

SM-non-Hodgkin lymphoma

Systemic mastocytosis with an associated clonal hematologic nonmast cell lineage disease

SM-AHNMD

Aggressive systemic mastocytosis

Mast cell leukemia

Mast cell sarcoma

ASM

MCL

MCS

Extra-cutaneous mastocytoma

ECM

aFor details of the WHO classification of mastocytosis, see Valent P et al: World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of the Haematopoietic and Lymphoid Tissues, edited by Jaffe ES et al. Lyon, IARC Press, 2001.

Table 149-2 Diagnostic Criteria for Systemic Mastocytosis (Major and One Minor or Three Minor Criteria Are Needed)a
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Table 149-2 Diagnostic Criteria for Systemic Mastocytosis (Major and One Minor or Three Minor Criteria Are Needed)a

Major

 Multifocal dense infiltrates of mast cells in bone marrow and/or other extracutaneous organs

Minor

 More than 25% of the ...

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