Hairy Cell Leukemia

Hairy Cell Leukemia

Hairy cell leukemia is a cancer of the bone marrow and blood, where white blood cells called lymphocytes become abnormal. Under the microscope the lymphocyte cells look hairy, thus the name.

Color enhanced SEM of hairy cell leukemia, (red blood ceel for comparison). Magnification = 1,700x at 35mm.

Diagnosing Hairy Cell Leukemia

Clinical signs

  • 25% present with abdominal fullness or discomfort due to splenomegaly, which may be massive.
  • Spontaneous splenic rupture may occur, which constitutes a medical emergency.
  • 25% present with systemic complaints such as fatigue, weakness, and weight loss. Patients do not usually complain of fever or night sweats.
  • Another 25% present either with bruising and bleeding secondary to severe thrombocytopenia, or with recurrent infections.
  • The remaining 25% is asymptomatic.

Hairy Cell Leukemia2


  • 60-80% of patients with HCL present with pancytopenia, with hematocrits in the range of 20-35%, a total white blood cell count usually below 4000/microL, and platelet counts in the range of 20,000 to 100,000/microL.
  • Hairy cells can be identified in Romanovsky-stained peripheral blood films from about 90% of patients.

Bone marrow biopsy

Bone marrow is hypercellular in most patients, and hairy cell infiltration may be diffuse, focal, or interstitial. In patients with diffuse involvement, large areas of the bone marrow may be replaced by hairy cells, with complete effacement of the bone marrow. When the bone marrow is focally involved, the infiltrates are randomly situated and may include paratrabecular locations.

The hairy cell nuclei are widely separated from each other by virtue of the cell’s abundant cytoplasm, giving a halo or “fried egg” appearance.