The most critical step in the clinical management of individuals with MBL is to insure the correct diagnosis. Individuals with MBL should be distinguished from patients with subtle manifestations of NHL. In the absence of constitutional symptoms (fevers, night sweats, fatigue, weight loss), individuals with CLL-like MBL can be distinguished from those with SLL based on the absence of palpable lymphadenopathy or organomegaly on physical exam (Table 3). Although marrow biopsy is not required, nearly all patients with clinically identified MBL will have some degree of bone marrow involvement if biopsy is performed.(27, 32) Although the median percent marrow involvement in clinical MBL appears to be between 10–20% more extensive involvement is observed in some individuals.(27, 32) In the series from Mayo Clinic, although 3/46 (6.5%) individuals with MBL had extensive marrow involvement on biopsy (70 to 80%) none of these 3 individuals had required treatment on up to 5 year follow-up.(32)
