Features for diagnosis:
(1) splenomegaly with hypersplenism
(2) splenic histology (micronodular lymphoid infiltrate of the splenic white pulp centered on lymphoid follicles; biphasic pattern with central zone of small lymphocytes and an outer zone of medium-sized cells with clear cytoplasm in the marginal zone)
(3) histology of bone marrow trephine biopsy (intrasinusoidal lymphocytes with or without micronodules)
(4) morphology of circulating lymphocytes
(5) immunophenotype (see below)
(6) exclusion of other small B-cell disorders (CLL, follicular lymphoma, mantle cell lymphoma, MALT lymphoma)
(7) variable monoclonal gammopathy
(8) variable autoimmune phenomenon
Lymphocytes in the peripheral blood show small lymphocytes:
(1) round nucleus with condensed chromatin
(2) basophilic cytoplasm
(3) short villi (may be loss if the specimen is stored in anticoagulant for a few hours)
Immunophenotype - positive for:
(1) CD20 and CD22
(2) surface IgM
(3) surface IgD
(4) FMC7
(5) CD79b
(6) CD27
Negative immunostaining: CD103, CD123, CD10, BCL6, CD23, annexin A1
