T-cell prolymphocytic leukaemia (T-PLL) is a clinicobiological entity that has no relationship to B-cell prolymphocytic leukaemia (B-PLL) other than some degree of similarity of cytological features [1, 2]. It is mainly a disease of the elderly. Ataxia telangiectasia predisposes . There is no relationship to human lymphotropic viruses I or II .
Typical clinical features are lymphadenopathy, hepatomegaly and splenomegaly. Skin infiltration is present in about one-fifth of patients . Serous effusions can occur. In most patients this is an aggressive disorder, although in a minority of patients the course is more indolent (smouldering T-PLL) .
Haematological and pathological features
The white cell count is usually high and anaemia and thrombocytopenia are common. Neoplastic cells can resemble those of B-PLL, being large with a round to oval nucleus, a moderate amount of cytoplasm and a prominent nucleolus; in some cases the nuclei are quite irregular (Figures 20.1,20.2,20.3). In the small cell variant of T-PLL the cells are not much larger than those of chronic lymphocytic leukaemia but differ in that the cytoplasm is more basophilic and there are cytoplasmic blebs; nuclei are irregular and a nucleolus is apparent. In the small cell variant the nucleolus is smaller and much less prominent than in cases with larger cells. The two cytological variants represent the same disease. In addition the condition initially described as 'Sézary cell leukaemia', in which the cells are medium sized with a highly convoluted nucleus, is now seen as a variant of T-PLL.
Peripheral blood film in T-PLL showing small and medium sized cells with irregular nuclei and nucleoli. Romanowsky, x 60 objective.
Peripheral blood film in T-PLL showing medium sized cells with basophilic cytoplasm and irregular nuclei with nucleoli. Romanowsky, x 100 objective.
Ultrastructure of a T-PLL cell showing an irregular nucleus with a prominent nucleolus. The arrow shows electron-dense granules, a feature of T-PLL and not B-PLL. Lead nitrate and uranyl acetate stain.
Bone marrow infiltration is variable, sometimes heavy interstitial and sometimes diffuse (Figure 20.4). Spleen histology shows marked infiltration of the red pulp with invasion of the white pulp and splenic capsule  (Figures 20.5 and 20.6). Skin infiltration is in the dermis, preferentially around the skin appendages, without epidermotropism (Figure 20.7). Lymph node infiltration is preferentially paracortical with sparing of the follicles but may become diffuse.
Section of bone marrow trephine biopsy specimen showing heavy interstitial ...