Identification of a pure splenic form of chronic lymphocytic leukaemia.

We have recently proposed a new staging system for chronic lymphocytic leukaemia (CLL) in which patients with isolated splenomegaly are classified into a distinct stage (stage II). Twenty-three such patients (from two institutions) have been studied without recorded death in a follow-up of 18 months to 30 years. This favourable prognosis justifies separation of these 'pure splenic forms' (SCLL) which must be distinguished from what Galton has termed prolymphocytic leukaemia (PL). This distinction can be made on the basis of three criteria: (i) Clinically, SCLL has a slow uneventful course and neither anaemia and/or thrombocytopenia: (ii) cytologically PL can be distinguished from other forms of CLL though atypical forms of CLL may be confused with the former; and (iii) the study of surface membrane immunoglobulins (SmIg) showed that while lymphocytes from most patients with both PL and SCLL bore uniform SmIg, suggesting a monoclonal B-cell proliferation, there was a major quantitative difference in that whereas PL lymphocytes had a number of antigenic sites close to that of normal lymphocytes (mean: 82 000 sites per cell), SCLL lymphocytes had a drastically reduced number of sites. It is our opinion that this is an important criterion for the differential diagnosis between PL and SCLL.