Hairy cell leukaemia (HCL) is an indolent lymphoproliferative disorder resulting from the proliferation of a neoplastic clone of morphologically and immunophenotypically distinctive mature B lymphocytes at a post-germinal stage of maturation [1,2]. Most patients are middle aged with a marked male predominance. Patients who present with advanced disease often show immune deficiency.
Characteristically there is splenomegaly without palpable lymphadenopathy, although up to one-third of patients have abdominal lymphadenopathy on computed tomography (CT) scanning. Prominent abdominal lymphadenopathy may be detected at relapse . Presentation may be with mycobacterial or other opportunistic infection.
Haematological and pathological features
There is cytopenia (sometimes bicytopenia or pancytopenia) with prominent monocytopenia. It is uncommon for the white cell count to be elevated. Monocytopenia is not a feature of other lymphoproliferative disorders and can thus be a useful clue to diagnosis. Hairy cells are medium sized with plentiful weakly basophilic cytoplasm with irregular margins (Figure 11.1). The nucleus may be round, oval, bean-shaped or dumb-bell-shaped and characteristically has a delicate chromatin pattern without an obvious nucleolus. Hairy cells may be infrequent in the peripheral blood and concentrating them in a buffy coat preparation can be useful. The degree of ‘hairiness’ of the neoplastic cells varies between films and even between different parts of the one blood film. Cells express tartrate-resistant acid phosphatase (Figure 11.2). On ultrastructural examination, a ribosomal lamellar complex is characteristic (Figure 11.3).
Peripheral blood film in hairy cell leukaemia showing a hairy cell with a bean-shaped nucleus and plentiful weakly basophilic irregular cytoplasm. Romanowsky stain, ×100 objective.
Tartrate-resistant acid phosphatase activity in hairy cells ×100 objective.
Ultrastructural features of a hairy cell, including ribosomal lamellar complexes. Electron microscopy.
The bone marrow is usually hard to aspirate and often aspiration is impossible. If an aspirate is obtained, hairy cells are usually more easily detectable than in the peripheral blood. If bone marrow cannot be aspirated, an imprint should be made from the trephine biopsy specimen. Trephine biopsy sections show bone marrow infiltration to be initially random focal and interstitial but with advanced disease it becomes diffuse (Figure 11.4). Cytological features on sections are very distinctive. The pale, rather bland, irregularly shaped nucleus is apparent and is surrounded by scanty irregular cytoplasm and then by an artefactual space, which is the result of cytoplasmic shrinkage. The result is that the neoplastic cells appear to be spaced apart (so called ‘fried-egg’ pattern). Erythrocytes may be present in the interstitium. Reticulin deposition is ...