Hairy cell leukemia diagnostic criteria and differential diagnosis

Abstract

Hairy cell leukemia (HCL) is a disease with distinctive clinical findings, as well as a unique morphology and immunophenotype. These features typically allow for a reliable and reproducible diagnosis in nearly all situations. However, certain morphological features of HCL, such as villous cytoplasmic projections or characteristic tissue specific infiltrative patterns, including red pulp expansion with pseudosinuses, may be seen in other B-cell lymphoproliferative disorders. A methodical and thorough approach evaluating the clinical, cytological, histological, architectural, and immunophenotypic features is described and will aid in rendering the appropriate diagnosis. This is paramount as current data indicate that hairy cell leukemia - variant and other splenic B-cell lymphomas must be distinguished from HCL, as the response to therapy differs in these disorders.

Figure 1.

Hairy cell leukemia, cytological features. (A) Peripheral blood smear showing characteristic ‘hairy’ cell with cytoplasmic projections and frayed cytoplasmic borders (×1000; Wright–Giemsa). (B) Touch preparation from spleen demonstrating representative hairy cells. Note loss of villous cytoplasmic projections (×1000; Wright–Giemsa).

Figure 2.

Hairy cell leukemia, bone marrow biopsy. (A) Bone marrow with relatively inconspicuous interstitial infiltrate of medium-sized lymphoid cells with ample cytoplasm (×200; H&E). (B) CD20 immunohistochemical stain aids in identification of neoplastic cells (×200; IHC).

Figure 3.

Hairy cell leukemia involving lymph node. Replacement of lymph node paracortex and interfollicular areas by a relatively monotonous infiltrate of medium-sized lymphoid cells with ample cytoplasm. Sinuses are widely patent (×40; H&E). Inset: high-power image of atypical infiltrate. The lymphoid cells have abundant cytoplasm and distinct cytoplasmic borders (×400; H&E).

Figure 4.

Differential diagnosis of hairy cell leukemia. (A) Peripheral blood with features of splenic lymphoma with villous lymphocytes (SLVL). This pattern is most commonly associated with diffuse red pulp small B-cell lymphoma. The cells have ample cytoplasm and villous cytoplasmic projections morphologically consistent with ‘hairy’ cells (×400; Wright–Giemsa). (B) CD20 immunohistochemical stain highlights the typical intrasinusoidal localization of the neoplastic cells (×40; IHC).