Secondary myelofibrosis Down syndrome

Laboratory features

• Peripheral blood shows a variety of abnormalities—usually pancytopenia with circulating blasts.

• WBC seldom >50 x 109/L though can occasionally be very high with symptoms of leucostasis—deafness, confusion and impaired consciousness.

• Bone marrow usually shows heavy overgrowth of blasts with different morphology depending on FAB type. Auer rods (abnormal elongated primary granules seen on Romanowsky stains in cytoplasm of malignant myeloblasts) are diagnostic of AML and are not found in health. Seen in all types of AML except M6 and M7, most common in M1/2/3, particularly M3.

• Cytochemistry may help; non-specific esterase positive in M4/M5 AML, not other types and myeloperoxidase positivity can help distinguish between poorly differentiated AML and ALL. M7 AML may develop extensive marrow fibrosis making aspiration difficult; trephine histology needed.

• Genetic abnormalities common in blast cells (see above).

• Immunophenotyping less important that in ALL, though essential for immediate diagnosis of M7 AML which has no distinguishing morphological or cytochemical features. CD antigens expressed vary according to FAB type; CD33 strongly +ve in all, CD13 in M2/3; CD4 in M4/M5 and CD41/61 in M7. M6 disease expresses glycophorin A.

Clinical features

Children with advanced AML are commonly more sick than those with ALL. They can present with bleeding, haemostatic failure and/or septicaemia as manifestations of marrow failure and profound neutropenia. Extramedullary chloromas (solid deposits of malignant cells) arise in around 10% of cases. They may precede marrow failure (or even detectable marrow infiltration). They can arise internally around the spine

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