A 42-year-old Indian man presents with a 3-month history of progressive abdominal distension and early satiety. On examination, he has massive splenomegaly and mild hepatomegaly. Laboratory investigations reveal hemoglobin 9.2 g/dL, WBC 68,000/μL with 60% lymphocytes, and platelets 95,000/μL. Peripheral blood smear shows small, mature-appearing lymphocytes with scant cytoplasm. Bone marrow biopsy shows nodular infiltration of small lymphocytes. Flow cytometry reveals CD5+, CD19+, CD23+ B cells. What is the most likely diagnosis?

Explanation

## Diagnosis: Chronic Lymphocytic Leukemia / Small Lymphocytic Lymphoma (CLL/SLL) ### Clinical Presentation The patient presents with: - Insidious onset (3 months) of abdominal symptoms - Massive splenomegaly and hepatomegaly - Cytopenias (anemia, thrombocytopenia) - Marked lymphocytosis (68,000/μL) with mature small lymphocytes **Key Point:** CLL/SLL is the most common B-cell lymphoma in Western countries and increasingly in India. It typically affects middle-aged to elderly patients and often presents with lymphocytosis discovered incidentally or with cytopenias. ### Immunophenotype — The Diagnostic Hallmark | Feature | CLL/SLL | Follicular | Marginal Zone | Lymphoplasmacytic | | --- | --- | --- | --- | --- | | **CD5** | **Positive** | Negative | Negative | Negative | | **CD19** | Positive | Positive | Positive | Positive | | **CD23** | **Positive** | Negative | Variable | Negative | | **Surface Ig** | Weak | Strong | Strong | Strong | | **Cytology** | Small, mature | Centrocytes, centroblasts | Small lymphocytes, monocytoid cells | Small lymphocytes, plasma cells | **High-Yield:** The **CD5+, CD19+, CD23+** phenotype is virtually pathognomonic for CLL/SLL. CD5 is a T-cell marker aberrantly expressed on B cells in CLL — this is the "coexpression" that clinches the diagnosis. ### Morphology & Bone Marrow - Small, mature lymphocytes with scant cytoplasm and clumped chromatin ("soccer ball" nuclei) - Nodular or diffuse infiltration of bone marrow - Smudge cells (fragile lymphocytes) often seen on blood smear **Clinical Pearl:** Massive splenomegaly in CLL suggests advanced disease (Rai stage III–IV or Binet stage C). The combination of lymphocytosis + organomegaly + cytopenias is classic for CLL. ### Why This Is CLL/SLL and Not Other Indolent Lymphomas **Follicular lymphoma** would show: - CD5−, CD10+, BCL2+ (t(14;18)) - Centrocytes and centroblasts in germinal center pattern - Typically nodal presentation, not massive splenomegaly **Marginal zone lymphoma** would show: - CD5−, CD23− (or weakly positive) - Monocytoid B cells in marginal zone pattern - Often associated with Sjögren's syndrome or hepatitis C **Lymphoplasmacytic lymphoma** would show: - CD5−, CD23− - Admixture of small lymphocytes and plasma cells - Often associated with Waldenström macroglobulinemia (monoclonal IgM) **Mnemonic:** **CD5-CD23 Co-Expression = CLL** — Remember: "**C**LL has **C**D5 and **C**D23." ### Staging & Prognosis This patient has: - Rai stage III (anemia, organomegaly) or Binet stage C (lymphocytosis + organomegaly + anemia) - Intermediate to poor prognosis - Requires monitoring for Richter transformation (10–15% risk) and autoimmune complications **High-Yield:** CLL/SLL is incurable with conventional chemotherapy but has improved survival with targeted agents (BTK inhibitors like ibrutinib, anti-CD20 monoclonal antibodies like rituximab).