Background. Mastocytosis is a heterogeneous group of hematological disorders characterized by expansion and accumulation of clonal mast cells in one or more organs, typically the skin and bone marrow. The classification of the World Health Organization (WHO) divides the disease into cutaneous mastocytosis, systemic mastocytosis and mast cell sarcoma. The diagnosis of systemic mastocytosis is based on the criteria proposed by the WHO.
Clinical presentation. 52 year old man was referred to the Vilnius University Hospital Santaros Klinikos because of itchy rash in the skin of neck and face. Serum tryptase level was found to be markedly elevated (>200 gg/L). Histological examination of the bone marrow trephine biopsy revealed deposition of mast cells and an infiltration by B-lymphoid cells. Immunohistochemically the mast cells exhibited an aberrant immunophenotype with expression of CD2 and CD25. Flow cytometry found that 0.03% of peripheral blood cells comprised mast cells with aberrant phenotype. The diagnosis of mast cell leukemia (an aleukemic variant) with associated hematologic neoplasm was established.
Conclusion. A comprehensive diagnostics is required for establishing a diagnosis of systemic mastocytosis. The diagnosis of this disorder is based on the WHO criteria, in which the serum tryptase level, histological, cytological and immunophenotypic evaluation of mast cells and molecular analysis are required. Diagnostic algorithms have been established to delineate an approach to patients with suspected mastocytosis. Mast cell leukemia is a very rare form of systemic mastocytosis characterized by at least 20% of mast cells in a bone marrow smear.