Pathology
Leukocyte Disorders
Leukocyte disorders for MBBS and NEET-PG: leucocytosis, leucopenia, leukaemoid reaction, and the acute and chronic myeloid and lymphoid leukaemias, mapped to NMC code PA18.1.
MedNext Academy | 3 min read
Leukocyte Disorders
Leukocyte disorders for MBBS and NEET-PG: leucocytosis, leucopenia, leukaemoid reaction, and the acute and chronic myeloid and lymphoid leukaemias, mapped to NMC code PA18.1.
This chapter covers disorders of white cells, from reactive changes to malignancy. It distinguishes leucocytosis and leucopenia from the leukaemoid reaction, and classifies and describes the acute and chronic, myeloid and lymphoid leukaemias with their key diagnostic features.
High-yield: Leukocyte Disorders
- Leucocytosis is a raised white cell count, most often a reactive neutrophilia in bacterial infection.
- Leucopenia is a reduced white cell count, with neutropenia carrying the greatest risk of infection.
- A leukaemoid reaction is a marked reactive leucocytosis that can mimic leukaemia, but with a high leucocyte alkaline phosphatase score.
- Leukaemia is a clonal malignant proliferation of white cells classified as acute or chronic, and myeloid or lymphoid.
- Acute leukaemia is characterised by more than 20% blast cells in the blood or marrow and a rapid clinical course.
- Acute lymphoblastic leukaemia is the most common malignancy of childhood and responds well to treatment.
- Acute myeloid leukaemia may show Auer rods, needle-shaped inclusions that are pathognomonic of myeloblasts.
- Chronic myeloid leukaemia is defined by the Philadelphia chromosome, a t(9;22) translocation producing the BCR-ABL fusion gene.
- Chronic myeloid leukaemia shows a marked leucocytosis with the full spectrum of granulocyte precursors and a low leucocyte alkaline phosphatase.
- Chronic lymphocytic leukaemia is a disease of older adults with mature small lymphocytes and smudge cells on the film.
- Tyrosine kinase inhibitors such as imatinib target the BCR-ABL protein and transformed the outlook in chronic myeloid leukaemia.
- The acute leukaemias present with the consequences of marrow failure: anaemia, infection and bleeding.
- Immunophenotyping by flow cytometry classifies leukaemias by their surface markers.
- The leucocyte alkaline phosphatase score is low in chronic myeloid leukaemia and high in a leukaemoid reaction, helping tell them apart.
Leukaemia essentials
- **Acute lymphoblastic:** Commonest childhood cancer; more than 20% blasts; good response to therapy.
- **Acute myeloid:** Myeloblasts with Auer rods; marrow failure features.
- **Chronic myeloid:** Philadelphia chromosome t(9;22), BCR-ABL; low LAP score.
- **Chronic lymphocytic:** Older adults; mature lymphocytes and smudge cells.
NMC competencies in this chapter
- **PA18.1:** Causes of leucocytosis and leucopenia and the classification and features of leukaemias
Frequently Asked Questions
How is acute leukaemia defined?
By the presence of more than 20% blast cells in the blood or bone marrow, together with a rapid clinical course driven by marrow failure.
What is the Philadelphia chromosome?
A t(9;22) translocation producing the BCR-ABL fusion gene, which defines chronic myeloid leukaemia and is targeted by imatinib.
How do you tell a leukaemoid reaction from chronic myeloid leukaemia?
The leucocyte alkaline phosphatase score is high in a reactive leukaemoid reaction and low in chronic myeloid leukaemia.
Which leukaemia is commonest in children?
Acute lymphoblastic leukaemia, which is the most common childhood malignancy and generally responds well to treatment.
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