The patient is a 59-year-old male who presented with chief complaints of fatigue and left upper quadrant abdominal pain. CT scan showed splenomegaly with spleen span of 26 cm.
Complete blood count showed pancytopenia and a monocytopenia (<0.1 k/uL). Peripheral blood smear examination showed relative lymphocytosis with atypical lymphoid cells.
A bone marrow study was performed, which showed a diffuse infiltrate of atypical lymphoid cells. A diagnosis of Hairy Cell leukemia was made, and the patient has been started on 2-chlorodeoxyadenosine (2-CdA) and is doing well.
Learning points:
1. Hairy cell Leukemia (HCL) is an indolent B cell malignancy involving spleen, peripheral blood and bone marrow. Classic cases present with pancytopenias including monocytopenia.
Bone marrow has a charaterstic dry tap owing to massive fibrosis, as fibrogenic growth factors are secreted by tumour cells in the marrow.
Spleen is massively enlarged with leukemic cells charaterstically infiltrating the red pulp.
2. Almost all hairy cell leukemia cases harbor the BRAF V600E mutation. Rare BRAF negative cases use the IGHV4-34.
3. Immunophenotyping reveals a neoplastic B cell population showing a bright CD20 alongwith aberrant expression of CD11c, CD25, CD103.
4. Annexin A1 is the most specific immunohistochemical marker for HCL, although TRAP and CD123 are often also positive. CD22 is uniformly bright.
5. HCL-v (Variant) often presents with Normal or increased blood counts, no monocytopenia, cells with prominent nucleoli and an aggressive course.
6. Treatment includes Cladribine and Pentostatin (Purine analogs), recently INF-alpha and a BRAF inhibitor- Vemurafenib have been tried and have proved efficacious in relapsed and refractory cases. More recently, immunotoxins such as moxetumomab Pasudotox (anti-CD22) are showing promising results.
