Mastocytosis is an emerging differential diagnosis in patients with more or less specific mediator-related symptoms. In some of these patients, typical skin lesions are found and the diagnosis of mastocytosis can be established. In other cases, however, skin lesions are absent, which represents a diagnostic challenge. In the light of this unmet need, we developed a diagnostic algorithm for patients with suspected mastocytosis. In adult patients with typical lesions of mastocytosis in the skin, a bone marrow (BM) biopsy should be considered, regardless of the basal serum tryptase concentration. In adults without skin lesions who suffer from mediator-related or other typical symptoms, the basal tryptase level is an important parameter. In those with a slightly increased tryptase level, additional investigations, including a sensitive KIT mutation analysis of blood leucocytes or measurement of urinary histamine metabolites, may be helpful. In adult patients in whom (i) KIT D816V is detected and/or (ii) the basal serum tryptase level is clearly increased (>25-30 ng/ ml) and/or (iii) other clinical or laboratory features suggest the presence of 'occult' mastocytosis or another haematologic neoplasm, a BM investigation is recommended. In the absence of KIT D816V and other signs or symptoms of mastocytosis

Aims: Although systemic mastocytosis (SM) with an associated clonal haematological non-mast cell lineage disease (SM-AHNMD) is a major subtype of SM, little is known about its frequency among myelogenous neoplasms, and mastocytosis in particular, or about AHNMD subtype frequencies.Methods: Approximately 19 500 routine bone marrow biopsies were evaluated. Immunostaining with antibodies against tryptase, KIT, and CD25 and molecular analysis for detection of C-KIT point mutations were performed in approximately 550/4100 myelogenous malignancies including mastocytosis, almost all subtypes of myelodysplastic syndrome (MDS), myelodysplastic/myeloproliferative syndrome (MDS/ MPD), MPD, and acute myeloid leukaemia (AML). Results: SM was rare-it was diagnosed in only 64 bone marrows (0.3%) and made up 1.5% of myelogenous tumours. SM-AHNMD was the second most frequent subtype (20). SM-AHNMD was never included in the clinical differential diagnoses and was confirmed histologically in most cases only after appropriate immunostaining. The abnormal mast cell phenotype was confirmed by immunohistochemical demonstration of tryptase and CD25 coexpression. The following associated haematological neoplasms were found: MDS/MPS, AML, MPS, MDS, plasma cell myeloma, and unclassifiable myelogenous malignancy. C-KIT point mutations were detected in 16 of 20 cases. Conclusions: SM-AHNMD can be diagnosed histologically in bone marrow trephines only after immunostaining with antibodies against tryptase, KIT, and CD25. Eighteen of 20 AHNMDs were of myeloid origin. C-KIT point mutations were present in 16 of 20 cases. The prognostic relevance of detecting SM associated with another haematological neoplasm remains unclear, but mast cell resistance to most cytoreductive agents is of major importance for treatment planning.

The clinical course of a 56-year-old female patient with Sweet's syndrome (SS) preceded by a myelodysplastic syndrome (MDS) is described. During the acute phase of the disease with high remittent fever, painful skin lesions and maximal leucocytosis IL-6 and G-CSF serum levels were extremely high, while TNF-alpha was only slightly elevated and gamma-interferon and IL1-beta were not increased. On clinical improvement IL-6 serum levels rapidly fell, whereas G-CSF values already slightly elevated before the manifestation of the disease slowly declined. High G-CSF levels triggered by a yet unknown factor could explain the leucocytosis, neutrophilic dermatosis and skin lesions in SS, while IL-6 probably induced the associated clinical symptoms of fever and pain.

Blood findings in 61 cases of generalized mastocytosis (GM) were evaluated. The cases were divided into two major variants: Systemic mastocytosis (SM; n = 34) with urticaria pigmentosa-like skin lesions, and malignant mastocytosis (MM; n = 27), without skin involvement. The following results were obtained: (1) Significant differences between MM and SM were found in the main haematological parameters (erythrocyte, platelet and leucocyte counts and haemoglobin level); normal values were found in 16 of the SM cases, but never in MM. (2) The main pathological findings were: in SM, anaemia (9/34) and leucocytosis (5/34); and in MM, leucocytosis (19/27), monocytosis (14/27), eosinophilia (12/27), bicytopenia (12/27, mostly anaemia with thrombocytopenia), basophilia (10/27) and isolated anaemia (7/27). (3) The major finding was a significant difference between MM and SM in the incidence of myeloproliferative disorders (MPD), myelodysplasia and mast cell leukaemia (MCL): these disorders occurred in 23 (92%) MM patients, but only in two (6%) SM patients (P less than 0.001). The four instances of MCL and two of myelodysplasia all occurred with MM. Of the 19 cases of MPD, six (SM, 1; MM, 5) were acute variants (acute myeloid and myelomonocytic leukaemias) and 13 (SM, 1; MM, 12) were chronic variants. No case of malignant lymphoma was noted. (4) The blood picture in 10 of 13 chronic MPD cases represented an atypical chronic myeloid leukaemia for which the preliminary descriptive term 'mastocytosis-associated MPD' is proposed. (5) A survey of 103 published cases (SM, 77; MM, 26) yielded similar findings, including a high incidence of MPD and MCL in MM. These findings add further weight to the argument for recognizing SM and MM as two separate entities.

Abnormal differentiation and maturation of hemopoietic cells are characteristic features of myelodysplastic syndromes (MDS). Tryptases (alpha- and beta-type) are lineage-restricted serine proteases primarily expressed in mast cells (MC). We have analyzed expression of tryptase in 89 de novo MDS patients (refractory anemia (RA), n = 30; RA with ringed sideroblasts (RARS), n = 21; RA with excess of blasts (RAEB/RAEB-t), n = 27; chronic myelomonocytic leukemia (CMML), n = 11). Serum levels of total tryptase (alpha - protryptase + beta - tryptase) were measured by FIA. The numbers of tryptase+ cells were determined in paraffin-embedded bone marrow (bm) sections by immunohistochemistry and morphometry. In healthy individuals, serum total tryptase levels ranged between < 1 and 15 ng/ml (5.6 +/- 2.8 ng/ml). Tryptase levels of > 20 ng/ml were detected in 5/22 patients with RA (22.7%), 4/17 with RARS (23.5%), 0/16 with RAEB/RAEB-t, and 3/8 with CMML (37.5%). Thus, serum tryptase concentrations were higher in RA (16.6 +/- 14.3 ng/ml), RARS (12.9 +/- 8.2), and CMML (16.5 +/- 7.6) compared to RAEB/-t (8.7 +/- 3.8). By morphometry, elevated numbers of tryptase+ bm cells were detected in all MDS groups (RA: 139 +/- 131; RARS: 118 +/- 98; RAEB/RAEB-t: 80 +/- 79; CMML: 105 +/- 114 cells/mm2) compared to controls (54 +/- 51 cells/mm2). As assessed by Northern blotting and protein analysis, bm cells in MDS primarily produced alpha-(pro)tryptase, but little or no beta-tryptase. Together, our data show that elevated levels of tryptase are detectable in a group of patients with MDS probably because of an increase in neoplastic (mast) cells producing the enzyme(s). In addition, serum tryptase levels appear to correlate with MDS variants. Follow up studies should clarify whether an elevated tryptase concentration in MDS is of prognostic significance.