WHO diagnostic criteria for SM
| Diagnostic criteria . |
|---|
| Major Criterion |
| Multifocal, dense infiltrates of mast cells (≥15 mast cells in aggregates) detected in sections of BM and/or other extracutaneous organs |
| Minor Criteria |
| a. In biopsy sections of BM or other extracutaneous organs, >25% of the mast cells in the infiltrate are spindle shaped or have atypical morphology or, of all mast cells in BM aspirate smears, >25% are immature or atypical. |
| b. Detection of an activating point mutation at codon 816 of KIT in BM, blood, or other extracutaneous organ. |
| c. Mast cells in BM, blood, or other extracutaneous organ express CD2 and/or CD25 in addition to normal mast cell markers.* |
| d. Serum total tryptase persistently exceeds 20 ng/mL (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid). |
| B Findings |
| 1. BM biopsy showing >30% infiltration by mast cells (focal, dense aggregates) and/or serum total tryptase level >200 ng/mL |
| 2. 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 slightly abnormal blood counts. |
| 3. Hepatomegaly without impairment of liver function, and/or palpable splenomegaly without hypersplenism, and/or lymphadenopathy on palpation or imaging. |
| C Findings |
| 1. BM dysfunction manifested by 1 or more cytopenia(s) (ANC <1.0 × 109/L, Hgb <10 g/dL, or platelets <100 × 109/L) but no obvious nonmast cell hematopoietic malignancy. |
| 2. Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension. |
| 3. Skeletal involvement with large osteolytic lesions and/or pathological fractures. |
| 4. Palpable splenomegaly with hypersplenism. |
| 5. Malabsorption with weight loss due to gastrointestinal mast cell infiltrates. |
| Diagnostic criteria . |
|---|
| Major Criterion |
| Multifocal, dense infiltrates of mast cells (≥15 mast cells in aggregates) detected in sections of BM and/or other extracutaneous organs |
| Minor Criteria |
| a. In biopsy sections of BM or other extracutaneous organs, >25% of the mast cells in the infiltrate are spindle shaped or have atypical morphology or, of all mast cells in BM aspirate smears, >25% are immature or atypical. |
| b. Detection of an activating point mutation at codon 816 of KIT in BM, blood, or other extracutaneous organ. |
| c. Mast cells in BM, blood, or other extracutaneous organ express CD2 and/or CD25 in addition to normal mast cell markers.* |
| d. Serum total tryptase persistently exceeds 20 ng/mL (unless there is an associated clonal myeloid disorder, in which case this parameter is not valid). |
| B Findings |
| 1. BM biopsy showing >30% infiltration by mast cells (focal, dense aggregates) and/or serum total tryptase level >200 ng/mL |
| 2. 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 slightly abnormal blood counts. |
| 3. Hepatomegaly without impairment of liver function, and/or palpable splenomegaly without hypersplenism, and/or lymphadenopathy on palpation or imaging. |
| C Findings |
| 1. BM dysfunction manifested by 1 or more cytopenia(s) (ANC <1.0 × 109/L, Hgb <10 g/dL, or platelets <100 × 109/L) but no obvious nonmast cell hematopoietic malignancy. |
| 2. Palpable hepatomegaly with impairment of liver function, ascites, and/or portal hypertension. |
| 3. Skeletal involvement with large osteolytic lesions and/or pathological fractures. |
| 4. Palpable splenomegaly with hypersplenism. |
| 5. Malabsorption with weight loss due to gastrointestinal mast cell infiltrates. |
The diagnosis of SM can be made when the major criterion and 1 minor criterion or at least 3 minor criteria are present.
ANC, absolute neutrophil count; Hgb, hemoglobin.
Mast cell CD25 expression can be detected by flow cytometry or immunohistochemistry. The latter is probably more reliable and practical in most hematopathology laboratories and may be the preferred methodology.