Lymphoid Disorders
Lymphoid neoplasms
Organize lymphoid disease by lineage (B, T/NK), maturation stage, and tempo. Small B-cell lymphomas usually present with lymphadenopathy, cytopenias, or incidental lymphocytosis; aggressive lymphomas present with rapid growth and B symptoms. Flow cytometry is the workhorse: clonality is shown by light-chain restriction in B cells or aberrant T antigens, and a panel usually suggests the entity.
Immunophenotype anchors: CLL/SLL is CD5+, CD23+, CD200+, FMC7−, with dim surface immunoglobulin; mantle cell lymphoma is CD5+, CD23−, cyclin D1+, with t(11;14); follicular lymphoma is CD10+, BCL2+, with t(14;18); marginal zone lymphoma is CD5−, CD10−, CD23−; hairy cell leukemia is CD11c+, CD25+, CD103+, CD123+, TRAP+, with BRAF V600E. Burkitt lymphoma shows medium cells, starry-sky pattern, near 100% Ki-67, and MYC rearrangement, usually t(8;14). DLBCL shows large cells and is subclassified by cell of origin. Classic Hodgkin lymphoma has Reed-Sternberg cells that are CD15+, CD30+, CD20− in an inflammatory background.
Plasma cell myeloma requires clonal plasma cells plus CRAB features (hypercalcemia, renal insufficiency, anemia, bone lesions) or SLiM criteria (≥60% clonal plasma cells, involved/uninvolved free light-chain ratio ≥100, or ≥2 MRI lesions). ALL is the common childhood leukemia: B-ALL blasts are TdT+, CD19+, CD10+; T-ALL is cytoplasmic CD3+. Risk stratification uses age, WBC, cytogenetics, and measurable residual disease.
Trap: reactive lymphocytosis from viral illness is pleomorphic and polyclonal and resolves; CLL is monomorphic and clonal. Do not label a young patient with lymphocytosis as CLL without flow.
Rule of thumb: a CD5-positive B-cell population that is CD23-positive with dim immunoglobulin is CLL until proven otherwise; check cyclin D1 to exclude mantle cell lymphoma.