Patterns of bone marrow involvement in chronic lymphocytic leukemia and small lymphocytic (well differentiated) non-Hodgkin's lymphoma. Its clinical significance in relation to their differential diagnosis and prognosis.

Forty-eight patients with chronic lymphocytic leukemia (CLL), and 12 patients with small (well differentiated) lymphocytic lymphoma (WDL) were histologically evaluated for their pattern of bone marrow (BM) involvement. Four different types of BM infiltration were recognized: nodular (N), interstitial (I), nodular and interstitial (mixed) and diffuse (D). The pattern of BM involvement was compared with the clinical, laboratory, and survival status in all patients. The extent of the disease in CLL patients, was determined by the Rai and the International Workshop on CLL Staging Systems, while in WDL patients the Ann Arbor staging system was used. In the CLL group the N pattern was found in 8%, the I in 33%, the mixed in 31%, and the D in 27% of the patients. Based on the International Workshop on CLL Staging System, the I pattern of BM involvement was more frequently found in Stage A (56%), the mixed in Stage B (68%), and the D in Stage C disease (90%). All CLL patients with D pattern required treatment from the beginning, contrary to CLL patients with the other patterns, in whom therapy was required in less than 50%. Similarly, deaths were more common in the D pattern in whom therapy pattern than in the other patterns. In the WDL patients BM involvement was found in 4 of 12, (33%) and its pattern of positivity was always nodular, although most patients (10 of 12) had advanced disease. It is concluded that the frequency of BM involvement may contribute in the differential diagnosis of WDL from CLL. In addition, the pattern of BM infiltration correlates very well with the International Staging System for CLL, and the pattern of BM positivity in CLL patients also has prognostic significance.