Peculiar Morphological, Cytochemical, Biochemical and Immunophenotyping Features in One Case of Acute Myeloid Leukaemia at the Onset.

On July 28^th 2005, a 53-year old woman was admitted to our Hematology Dpt. with fever (37.5 C), fatigue, marked gingiva hypertrophy, mild hepatomegaly and absence of lymphoadenopaty and splenomegaly. Laboratory tests showed high leukocyte count of 182 x10⁹/L, moderately increased platelet count (438 x10⁹/L), normocytic anemia (10,9 g/dl, MCV 84 fl). Biochemical parameters, including lysozyme, were in the normal range except for high level of lactate dehydrogenase (2524 UI/l). Peripheral blood (PB) smear showed the presence of 94% of blasts, without evident granules. At the cytochemical myeloperoxidase staining blast cells revealed the presence of single or multiple Auer rods, while cytoplasmic granules were positive to the α-naphtyl butyrate esterase. In the bone marrow (BM) aspirate blasts were 80% showing same morphological and cytochemical features as in peripheral blood, while the granulocytic maturating series was 14%. No evidence of morphologically identifiable monocytic series in PB neither in BM. Megakariocytes were slightly increased and there was trilineage dysplasia. Blast immunophenotyping in PB and in BM was as follow: CD45, CD33, CD13, CD7 and HLA-Dr positive, 36% MPO positive and 48% co-express CD11c an CD117. Moreover blasts were CD14, CD19 and CD56 negative. FAB diagnosis was AML-M4. Interphase Fluorescence in situ Hybridization (FISH) for detection of AML1/ETO and bcr/abl gene rearrangements was negative. After treatment with 2 g hydroxyurea and leucapheresis, the WBC count was still high (140 x10⁹/L) while after 1g of aracytin, WBC count decreased to 31000/mm^3. Patient is presently enrolled into the GIMEMA protocol AML-12.

This case shows at the onset following abnormalities:

• - an increased platelet count is a rare evenience in an AML at the onset;

• - negativity for lysozyme;

• - absence of CD14;

• - presence of Auer rods in quite all the blast population, which is a very rare evenience associated with monocytic subtypes of acute myeloblastic leukemia (AML);

• - atypical homogenous cytochemical pattern of blasts, showing Auer rods MPO positive and granules ANBE positive;

• - absence of any morphological differentiation of monocytic series. S4479