A 38-year-old man from Delhi presents with a 3-month history of progressive abdominal distension and early satiety. On examination, he has hepatosplenomegaly and generalized lymphadenopathy. Laboratory investigations reveal hemoglobin 9.2 g/dL, WBC 3.8 × 10⁹/L with atypical lymphocytes on blood smear, and LDH 680 U/L. A bone marrow biopsy shows hypercellular marrow with infiltration by abnormal lymphoid cells. Flow cytometry demonstrates CD5+, CD19+, CD23+ B lymphocytes. A lymph node biopsy shows diffuse infiltration with small lymphocytes and prolymphocytes, with some larger cells present. What is the most likely diagnosis?

Explanation

## Diagnosis: Chronic Lymphocytic Leukemia (CLL) ### Clinical Presentation The patient presents with a classic triad of CLL: - Insidious onset with constitutional symptoms (abdominal distension, early satiety from splenomegaly) - Hepatosplenomegaly and generalized lymphadenopathy - Cytopenias (anemia, mild leukopenia) ### Diagnostic Criteria Met | Feature | Finding | Significance | |---------|---------|---------------| | **Peripheral blood** | Atypical lymphocytes, WBC 3.8 × 10⁹/L | Absolute lymphocytosis (>5 × 10⁹/L diagnostic, but early CLL can present lower) | | **Flow cytometry** | CD5+, CD19+, CD23+ | Pathognomonic for CLL (B-cell marker + T-cell marker CD5 co-expression) | | **Bone marrow** | Hypercellular with lymphoid infiltration | Confirms marrow involvement | | **LDH** | 680 U/L (elevated) | Prognostic marker; indicates higher tumor burden | ### Key Point: **CD5+ CD19+ CD23+ B lymphocytes = CLL.** This immunophenotype is virtually diagnostic. CD5 is normally a T-cell marker; its co-expression with B-cell markers (CD19, CD23) is the hallmark of CLL. ### Pathology Features - Small, mature-appearing lymphocytes with scant cytoplasm - "Smudge cells" (fragile lymphocytes) on blood smear - Diffuse infiltration pattern in lymph nodes (vs. nodular pattern in follicular lymphoma) ### High-Yield: **CLL is the most common leukemia in adults in Western countries and increasingly in India.** The CD5+/CD23+ phenotype distinguishes it from mantle cell lymphoma (CD5+/CD23−) and follicular lymphoma (CD5−/CD23+). ### Clinical Pearl: CLL often presents incidentally on routine blood work in asymptomatic patients; symptomatic presentation (as in this case) suggests more advanced disease and warrants staging (CT chest/abdomen, LDH, β2-microglobulin) and risk stratification (FISH for del(13q), del(11q), del(17p), TP53 mutation). ### Mnemonic: **CLL = CD5 + CD19 + CD23 + (mature B cells)** --- ## Why Other Options Are Incorrect ### Follicular Lymphoma - Typically **CD5−, CD23+, CD10+** (germinal center B-cell origin) - Presents with painless lymphadenopathy but **not** with bone marrow involvement and cytopenias as prominently - Flow cytometry would NOT show CD5 positivity ### Mantle Cell Lymphoma - **CD5+, CD23−** (critical distinction from CLL) - Presents with advanced-stage disease, often GI involvement - Cyclin D1+ (t(11;14) translocation) — would be detected on FISH/molecular studies - More aggressive course than CLL ### Marginal Zone Lymphoma - Typically **CD5−, CD23−** (or weakly positive) - Often extranodal (MALT lymphoma) or splenic - Does not typically present with this degree of bone marrow infiltration and the characteristic CD5+/CD23+ phenotype