FRCPath Haematology Part 2: Morphology Mature B Cell Disorders Hairy Cell Variant

Morphological features:

  • Typically associated with leukocytosis
  • Atypical lymphoid cells are larger than normal lymphocytes
  • Abundant, weakly-basophilic cytoplasm with irregular projections which are thread-like
    • May be easier to see projections in the thicker part of the film
  • Nuclear outline is typically regular – round or oval
    • Occasionally kidney, dumbbell or bi-lobed
  • Generally prominent nucleoli
  • No monocytopaenia
Peripheral blood film from a patient with variant hairy cell leukaemia. Note the prominent nucleoli and adjacent monocyte. Atypical lymphocytes in hairy cell leukaemia generally lack nucleoli, which helps to distinguish hairy cell variant. HCLv also tends to present with a high WBC, as opposed to low WBC in HCL.
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Clinical features:

  • Splenomegaly
  • No lymphadenopathy
  • Symptoms and signs of pancytopaenia

Differential diagnosis:

  • Marginal zone lymphoma (less cytoplasm which is more basophilic, no monocytopaenia)
  • Hairy cell leukaemia (no nucleoli, marked monocytopaenia)

Investigations:

  • Flow cytometry: CD20+/11c+/103+/25-/123-/200-
  • BRAF mutation negative
  • Annexin A1 and TRAP negative
  • 50% have TP53 abnormalities and MAP2K1 mutations
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