An 8-year-old Iraqi male presented with fever and pallor of 2-months duration. There was no lymphadenopathy, splenomegaly or hepatomegaly. A full blood count showed: hemoglobin concentration 6.9 g/dl, white blood cell count 1.5 × 109/l and platelet count 217 × 109/l. Examination of a bone marrow aspirate showed acute myeloid leukemia (AML) with little maturation; blast cells were 85% of nucleated cells, and the case was classified as FAB (French–American–British) M1 AML. An unusual feature was the presence not only of Auer rods (left) but also of pseudo-Chédiak-Higashi inclusions, which on a Romanowsky stain varied from pink to deep purple (right). In addition to typical thin Auer rods there were also thick rod-shaped inclusions (left and right).
Pseudo-Chédiak-Higashi inclusions are observed occasionally in AML1 (including acute promyelocytic leukemia) and also, rarely, in refractory anaemia with excess of blasts.2 The inclusions are formed by fusion of azurophilic (primary) granules and show myeloperoxidase activity and Sudan black B staining. On ultrastructural examination they are heterogeneous and, in contrast to the inclusions seen in the inherited anomaly, contain rod-shaped structures showing periodicity.1 The diagnostic significance of these inclusions is likely to be similar to that of Auer rods, indicating either AML or a high grade myelodysplastic syndrome.