Hairy cell leukemia (HCL) has been mainly reported from the Western countries. Herein we describe
a case of HCL diagnosed in a Thai patient. A 36-year-old man presented with abdominal discomfort, frequent
gum bleeding and significant weight loss for 2 months. Physical examination revealed moderate anemia,
petechial hemorrhage on the extremities and an enlarged spleen down to the umbilicus. No hepatomegaly or
lymphadenopathy was detected. Complete blood counts revealed a hemoglobin (Hb) of 6.6 g/dL, a white
blood cell (WBC) count of 1.6x109/L (neutrophil 16%, lymphocyte 71%, monocyte 11%, atypical lymphocyte
1%), and a platelet (PLT) count of 17x109/L. Abnormal large mononuclear cells with villous projections were
seen in the blood smear. Although bone marrow (BM) aspiration resulted in a dry tap, abnormal lymphocytes
with villous projections could again be identified in the touch preparation. Flow cytometric analysis showed
a distinct population above the normal lymphocyte region on CD45/SSC gates with a strong expression of
CD19, CD20, CD22, CD25, CD11c, and kappa. CD5, CD23, CD10, CD4, and CD8 were all negative. BM
biopsy was consistent with HCL. The patient was treated with splenectomy followed by 8 cycles of fludarabine
and cyclophosphamide chemotherapy. At 21 months after diagnosis, the patient was doing well with a Hb of
16.9 g/dl, a WBC count of 6.8x109/L, neutrophil 49.9%, lymphocyte 39.6%, monocyte 8.6%, and a PLT count
of 329x109/L). No abnormal lymphoid cells were detected in the blood smear. This present report represents
the first Thai HCL case that was immunophenotypically confirmed by flow cytometry and successfully treated
at Siriraj Hospital.

Keywords: Hairy cell leukemia, lymphoid neoplasms, flow cytometry, splenectomy, fludarabine