Table 2.
Major variants of systemic mastocytosis and B and C findings
| ISM |
| Meets criteria for SM. No C findings and no evidence of an AHNMD. The mast cell burden is low, and skin lesions are frequently present. |
| a. Bone marrow mastocytosis: ISM with BM involvement, but no skin lesions |
| b. Smoldering SM: ISM, but with 2 or more B findings, but no C findings. Usually with skin lesions |
| SM-AHNMD* |
| Meets criteria for SM and criteria for an AHNMD (MDS, MPN, MDS/MPN, AML, or other WHO-defined myeloid hematologic neoplasm, with or without skin lesions). |
| ASM |
| Meets criteria for SM. One or more C findings. No evidence of mast cell leukemia. Variable involvement by skin lesions. |
| MCL |
| Meets criteria for SM. Bone marrow biopsy shows a diffuse infiltration, usually compact, by atypical, immature MCs. Bone marrow aspirate smears show 20% or more MCs. Typical MCL: MC comprise 10% or more of peripheral blood white cells. Aleukemic MCL: < 10% of peripheral blood white cells are MCs. Usually without skin lesions. |
| B findings |
| Bone marrow biopsy showing > 30% infiltration by MCs (focal, dense aggregates) and serum total tryptase level > 200 ng/mL. |
| Signs of dysplasia or myeloproliferation, in non–mast-cell lineage(s), but insufficient criteria for definitive diagnosis of a hematopoietic neoplasm (AHNMD), with normal or only slightly abnormal blood counts. |
| Hepatomegaly without impairment of liver function, and/or palpable splenomegaly without hypersplenism, and/or lymphadenopathy on palpation or imaging (> 2 cm). |
| C findings† |
| Bone marrow dysfunction manifested by 1 or more cytopenia (ANC < 1 × 109/L, Hb < 10 g/dL, or platelets < 100 × 109/L) |
| Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension |
| Skeletal involvement with large osteolytic lesions and/or pathologic fractures |
| Palpable splenomegaly with hypersplenism |
| Malabsorption with weight loss from gastrointestinal tract mast cell infiltrates |
*
A lymphoproliferative disorder or plasma cell dyscrasia may rarely be diagnosed with SM.
†
Must be attributable to the MC infiltrate.