Benign and Malignant Leukocyte Disorders
Benign and malignant leukocyte disorders
Benign leukocyte changes are common and must be distinguished from neoplasia. Neutrophilia with left shift, toxic granulation, and Döhle bodies suggests infection or stress; leukemoid reactions can mimic leukemia but have a high leukocyte alkaline phosphatase (LAP) score. Pelger-Huët anomaly is a benign nuclear hyposegmentation. Lymphocytosis in adults is often viral or CLL; monocytosis, eosinophilia, and basophilia each have reactive and clonal causes. Malignant disorders are classified by lineage, maturation, and genetics. AML requires ≥20% blasts except for defining abnormalities such as t(15;17), t(8;21), and inv(16). APL is an emergency because of DIC. CML shows marked left shift, basophilia, low LAP, and BCR-ABL1. CLL is CD5+, CD23+, with dim surface immunoglobulin and smudge cells. Hairy cell leukemia is TRAP positive, BRAF V600E, CD103/CD25/CD11c. ALL expresses TdT and CD19/CD10 (B-ALL). MDS shows cytopenias, dysplasia, and ring sideroblasts. Flow cytometry, cytogenetics, FISH, and molecular testing are integral.
Traps: blast percentage is not the sole criterion for AML with defining translocations. Smudge cells are an artifact and not diagnostic alone. A leukemoid reaction vs CML is resolved by LAP and BCR-ABL1. Pseudo-Pelger-Huët can be seen in MDS. Basophilia is a clue to CML.
Worked example: WBC 80 ×10^9/L with left shift, basophilia, and low LAP suggests CML; confirm with BCR-ABL1.