A 72-year-old woman from Bangalore presents with a 3-year history of progressive lymphadenopathy and fatigue. She denies fever or night sweats. Physical examination reveals generalized lymphadenopathy (cervical, axillary, inguinal) and mild splenomegaly. Complete blood count: WBC 18,500/μL (85% small mature-appearing lymphocytes, 10% prolymphocytes, 5% smudge cells), Hb 9.8 g/dL, platelets 95,000/μL. Flow cytometry shows CD5+, CD19+, CD23+ B cells. Bone marrow biopsy shows lymphoid infiltration (40% lymphocytes). What is the most likely diagnosis?

Explanation

## Diagnosis: Chronic Lymphocytic Leukemia (CLL) ### Clinical Presentation **Key Point:** Insidious onset of lymphadenopathy and cytopenias over years in an elderly patient, with predominantly small mature lymphocytes and characteristic immunophenotype, defines CLL. ### Diagnostic Criteria | Feature | Finding | Diagnostic Significance | |---------|---------|------------------------| | **Age** | 72 years | Median age at diagnosis 70–72 years | | **WBC count** | 18,500/μL | Lymphocytosis (>5,000/μL required for diagnosis) | | **Lymphocyte morphology** | Small, mature-appearing | **Hallmark**—not blastic, not prolymphocytes | | **Smudge cells** | Present (5%) | Fragile lymphocyte nuclei; artifact of blood smear | | **CD5+, CD19+, CD23+** | **POSITIVE** | **Pathognomonic immunophenotype for CLL** | | **Bone marrow** | 40% lymphocytes | Marrow involvement confirms diagnosis | | **Lymphadenopathy** | Generalized | Present in 80% of CLL patients | | **Splenomegaly** | Mild | Present in 50% | | **Cytopenias** | Hb 9.8, Plt 95K | Mild anemia and thrombocytopenia from marrow infiltration | ### Immunophenotype: The Gold Standard **High-Yield:** CLL is defined by the **CD5+/CD19+/CD23+ B-cell phenotype**. This is the most reliable diagnostic marker. ```mermaid flowchart TD A[B-cell lymphocytosis]:::outcome --> B{CD5 positive?}:::decision B -->|Yes| C{CD23 positive?}:::decision B -->|No| D[Not CLL]:::outcome C -->|Yes| E[CLL]:::action C -->|No| F[Mantle cell lymphoma]:::action ``` **Mnemonic:** **CLL = CD5, CD19, CD23** ("CLL loves CD23"—distinguishes it from mantle cell lymphoma, which is CD5+/CD23−). ### Differential Diagnosis | Diagnosis | WBC | Morphology | CD5 | CD23 | Key Difference | |-----------|-----|-----------|-----|------|----------------| | **CLL** | 18.5K | Small mature lymphs | + | + | Indolent; elderly; smudge cells | | **Prolymphocytic leukemia (PLL)** | Often >100K | Larger cells, prominent nucleoli | + (T-PLL) or − (B-PLL) | − | Aggressive; >55% prolymphocytes; worse prognosis | | **Mantle cell lymphoma** | Variable | Small to medium cells | + | − | Cyclin D1+; t(11;14); aggressive | | **Lymphoplasmacytic lymphoma** | Low-normal | Mixed small lymphs + plasma cells | − | − | Waldenstrom macroglobulinemia; monoclonal IgM | **Clinical Pearl:** Smudge cells (basket cells) are a hallmark of CLL—they result from the fragility of CLL lymphocytes during blood smear preparation. They are virtually pathognomonic. ### Staging (Rai Staging System) **Key Point:** This patient with lymphadenopathy, splenomegaly, and mild cytopenias is **Rai Stage II** (lymphocytosis + lymphadenopathy + organomegaly, no severe cytopenias). ### Management **High-Yield:** Many CLL patients (especially early stage) follow a "watch and wait" strategy—no treatment until symptomatic or progressive disease. When treatment is needed, first-line agents include: - Chemoimmunotherapy (fludarabine + rituximab) - Targeted therapy: BTK inhibitors (ibrutinib), BCL2 inhibitors (venetoclax) [cite:Robbins 10e Ch 13]