Hairy cell leukaemia and hairy cell variant
Hairy cells are generally first identified by their typical morphological features. Immunophenotype can be greatly helpful in establishing the diagnosis, and hairy cell leukaemia has characteristic molecular features. The major diagnostic challenge is to distinguish the variant disorder (HCL-V) and occasionally a splenic marginal zone lymphoma (SMZL). The clinical distinction is important and other diagnostic methods should be used to confirm these diagnoses.
- A medium sized mature lymphocyte with round, oval or kidney-shaped nucleus
- Nuclear chromatin is partly condensed and nucleolus is generally absent
- Cytoplasm is extensive and grey-blue without granulation or clear golgi body visible
- Typical fine "hairy projections" are characteristic and best seen in thicker parts of the blood film
- Monocytopenia is characteristic of typical HCL
Hairy cell leukaemia
Typical hairy cells viewed in the best area of the blood film - a slightly thicker area demonstrates the hairy processes more effectively (this is not genuine rouleaux, the image has been taken from an area where red cells are more packed). Note the typical oval or indented nucleus with a chromatin pattern that is less condensed than in a typical LPD, but is not "blast-like". The cytoplasm has a pale blue appearance and is relatively abundant with very typical fine "hairy" projections. When viewing films with possible hairy cell leukaemia remember that the number of abnormal cells is often low, with many normal forms also present. Also that an absence of monocytes is typical of the disorder.
AUDIO COMMENTARY: The morphology of Hairy cell leukaemia
IMMUNOPHENOTYPIC RECOGNITION OF HCL and HCL-V
Typical hairy cells share an activated phenoptype with other LPDs, but with the additional high expression of particular adhesion receptors (CD11c and CD103) or cytokine receptors (CD25 and CD123). Immunophenotyping may allow confident diagnosis, but molecular testing and bone marrow ttephine may also demonstrate characteristic diagnostic features.