Presentation:
(1) high white blood cell count (may be > 100,000 per µL); this may be high enough to result in leukostasis
(2) bleeding disorder with thrombocytopenia, prolonged PT and prolonged PTT
(3) A microangiopathic hemolytic anemia may be present.
Features of leukemic cells:
(1) Blasts in the peripheral blood have no, few or very small cytoplasmic granules.
(2) Auer rods are usually rare or absent but often can be found; "faggot" cells are possible.
(3) The nucleus may be folded, bilobed or irregular.
(4) The cells may be misdiagnosed as another form of leukemia (monocytic, T cell, etc).
(5) Blasts in the bone marrow may show the granules of typical M3.
Cytochemical pattern: myeloperoxidase and Sudan Black B positive; often chloroacetate esterase positive; occasionally alpha-naphthyl butyrate esterase positive
Immunoperoxidase pattern:
positive: CD33, CD13
negative: HLA-DR, CD34, CD14, CD11b, CD41
variable: T-cell associated surface antigen
Cytogenetic finding: usually t(15;17); less often t(11;17) or t(5;17)
PCR: presence of PML-retinoic acid receptor alpha (RAR-alpha) fusion gene product
