B-cell prolymphocytic leukaemia (B-PLL) is a rare lymphoproliferative disorder resulting from a clonal proliferation of mature B lymphocytes with specific cytological features  in the absence of previous or concurrent chronic lymphocytic leukaemia (CLL). Prognosis is generally poor but a more indolent form of the disease has also been recognised .
The disease affects mainly the elderly and is more common in men than in women. Splenomegaly is characteristic with lymphadenopathy usually being minor.
Haematological and pathological features
The white cell count is often high and about half of patients have anaemia and thrombocytopenia. In one study, prolymphocytes constituted more than 55% of circulating cells and this was suggested as a diagnostic cut-off point . However, it should be noted that a large proportion of prolymphocytes is also occasionally observed in advanced CLL and this cut-off point is therefore arbitrary. Prolymphocytes are medium to large lymphoid cells with a single prominent nucleolus (Figures 4.1, 4.2, 4.3); perinucleolar chromatin condensation gives the nucleolus a vesicular appearance. In some patients, cells are fairly uniform in size whereas in others there is a range from medium to large. When smaller cells are present, their nucleoli are usually smaller and less prominent.
Peripheral blood film from a patient with B-cell prolymphocytic leukaemia (B-PLL) showing one smear cell and a fairly uniform population of medium-sized lymphoid cells with large prominent nucleoli. Romanowsky stain, ×60 objective.
Peripheral blood film from a patient with B-PLL showing mainly medium-sized prolymphocytes and one very large cell. Romanowsky stain, ×100 objective.
Peripheral blood film from a patient with B-PLL showing two prolymphocytes, one of which is binucleated. Romanowsky stain, ×100 objective.
The trephine biopsy shows an interstitial/nodular or diffuse pattern of infiltration. Lymph node infiltration is diffuse, sometimes with a vaguely nodular pattern. Splenic infiltration is in both red and white pulp and in the white pulp it may be nodular (Figures 4.4 and 4.5).
Section of spleen from a patient with B-PLL showing prominent white pulp infiltration. Haematoxylin and eosin (H&E) stain, ×10 objective.
Section of spleen from a patient with B-PLL showing large cells with large nuclei containing prominent eosinophilic nucleoli. H&E stain, ×100 objective.
A low concentration paraprotein, most often immunoglobulin (Ig) M, may be present.