A 69-year-old male presented with weakness and splenomegaly.
WBC = 2.7 K/ul (52% lymphocytes, 12% neutrophils, 34% monocytes, 1%
eosinophils, 1% basophils), hematocrit = 33%, platelet count = 43 K/ul.
Bit Map B Data
What is your diagnosis?
The peripheral blood smear reveals medium-sized lymphoid cells with
delicate cytoplasmic projections. The nuclei are oval, slightly
indented and the chromatin pattern has a lacelike appearance. The
pale-blue cytoplasm has a fluffy texture and the cell border is
irregular. The cytochemical stains demonstrate acid phosphatase
activity resistant to inhibition by tartaric acid (TRAP positivity).
These morphologic features and cytochemical findings are
characteristics of Hairy Cell Leukemia (HCL).
Examination of the bone marrow biopsy reveals an infiltration of
mononuclear cells with abundant clear to lightly eosinophilic
cytoplasm, causing the individual nuclei to be evenly and widely
spaced, imparting a fried-egg appearance. In HCL, mast cells are often
prominent and lymphocytes and plasma cells may be admixed. Bone marrow
reticulin is characteristically increased, which probably accounts for
the high frequency of dry taps in patients with HCL. In the spleen, HCL
is characterized by involving solely the red pulp, both the cords and
The flow cytometry studies reveal a monoclonal population of cells
that express the pan-B cell marker, CD 19, and also express CD 11c and
CD 25. CD 11c was originally raised against hairy cells, and recognizes
a leukocyte adhesion molecule which is also present on monocytes and
macrophages, granulocytes, some activated T cells and in T
lymphoproliferative disorders. CD 11c is expressed strongly in
virtually all cases of HCL and only occasionally on B
lymphoproliferative processes other than HCL. CD 25 is the p55 receptor
for interleukin 2 and is more specific for HCL than CD 11c. However, a
minority of cases of HCL are CD 25 negative.
Included in the differential diagnosis of HCL are Splenic Lymphoma
with Villous Lymphocytes (SLVL), Monocytoid B Cell Lymphoma (MBCL), and
Prolymphocytic Leukemia (PLL). SLVL is morphologically very similar to
HCL, expresses the HCL marker CD 11c, and sometimes demonstrates TRAP
positivity. SLVL, however, is CD 25 negative and is confined to the
white pulp in the spleen. MBCL may demonstrate the fried egg pattern
similar to that of HCL is tissue sections. However, MBCL usually does
not present with splenomegaly, peripheral blood or bone marrow
involvement. In addition, MBCL is CD 25 and TRAP negative. PLL is
sometimes included in the differential diagnosis because both
peripheral blood and spleen are often involved. The prominent nucleoli
of PLL and extremely high leukocyte count usually help to establish the
diagnosis of PLL. Phenotypically, the CD 11c, CD 25 and TRAP negativity
distinguish PLL from HCL.
HCL is an uncommon lymphoproliferative disorder that primarily
affects elderly white men. Patients are often pancytopenic and have
enlarged spleens are presentation. Peripheral lymphadenopathy is
usually inconspicuous. The clinical course of HCL is indolent and
treatment is usually not required until severe pancytopenia occurs.
Most patients eventually will develop progressive disease, however.
Following splenectomy, a minority of patients experience longlasting
improvement without further treatment.
Hairy cell leukemia
- Chang KL et al: Hairy Cell Leukemia - Current Status. Am J Clin
Pathol 97:719-738, 1992.
- Hounieu H, Chittal S et al: Hairy Cell Leukemia. Am J Clin Pathol
Beth B. Hewitt, M.D.
Department of Pathology
University of Virginia Health System.
Donald J. Innes, Jr., M.D.
Department of Pathology
University of Virginia Health System
Questions should be addressed to