Hairy Cell Leukemia

Historical Names

• Known by various names in the past:
  • Histiocytic leukemia
  • Malignant reticulosystem
  • Lymphoid myelofibrosis
  • Leukemic reticulo-endothelial system

Characteristics

• Rare Type: Indolent (subtle) leukemia
• Subtype of CLL: Chronic Lymphocytic Leukemia
• Association: Often associated with Non-Hodgkin's Lymphoma
• Mutation: BRF V600E mutation
• Over-expression: Cyclin D1
• Demographics: Affects middle-aged Caucasian males

Pathophysiology

• Accumulation in the spleen → Splenomegaly → Early satiety & abdominal discomfort
• Crowding out cell lines:
  • RBCs → Symptoms of anemia
  • WBCs → Symptoms of leukopenia
  • Platelets → Symptoms of thrombocytopenia

Theories

• Linked to farming and gardening activities
• High tumor burden possibly associated with low cholesterol levels in blood

Bone Marrow and Spleen

• Hairy cells accumulate in bone marrow
• Reticulan fibers cause bone marrow fibrosis → Dry tap during aspiration
• Splenomegaly common
• Hepatomegaly sometimes present
• Reduced humoral & cell-mediated immunity by B and T-lymphocytes
• No significant lymphadenopathy

Clinical Features

• Symptoms of anemia, leukopenia, thrombocytopenia
• Cutaneous vasculitis in some cases

Laboratory Findings

• Peripheral Smear: Lymphocytes with cytoplasmic (hairy) projections
• Staining: Positive to TRAP (tartrate-resistant acid phosphatase)
• Immunohistochemistry (Flow Cytometry):
  • CD103+, CD11c+, CD25+
  • B-cell markers: CD19+, CD20+, CD22+
  • Annexin A1: Specific but not sensitive

Bone Marrow Examination

• Usually yields a dry tap due to fibrosis
• If aspirated successfully: Neoplastic cells and reticulan fibrosis

Diagnostic Questions (For Study Practice)

1. What’s the most likely diagnosis?
2. Next steps in diagnosis?

• t(9;22) translocation
  • Perform PAS stain
  • Immunophenotyping
  • Test for cryoglobulins

3. Red blood cell abnormalities → Potential causes?

Summary

• Old names clarified
• Relationship to spleen, symptoms, and demographic prevalence

Final Notes

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