70 year old male presented with 3-months history of generalised weakness. On examination, bilateral axillary lymphadenopathy was noted. Histopathological examination of enlarged lymph node showed effacement of lymph node architecture by diffuse proliferation of small-sized, mature-appearing lymphoid cells. Peripheral blood showed lymphocytosis with presence of CD5-positive and CD23-positive B-cells. Which of the following is the most likely diagnosis of this patient?

## **Core Concept**
The patient's presentation suggests a lymphoproliferative disorder, characterized by generalized weakness, bilateral axillary lymphadenopathy, and lymphocytosis with specific immunophenotypic markers (CD5-positive and CD23-positive B-cells). The histopathological findings of effacement of lymph node architecture by diffuse proliferation of small-sized, mature-appearing lymphoid cells further support this diagnosis.

## **Why the Correct Answer is Right**
The presence of CD5-positive and CD23-positive B-cells in the peripheral blood is highly suggestive of **Chronic Lymphocytic Leukemia (CLL)**. CLL is a type of non-Hodgkin lymphoma characterized by the clonal proliferation of mature, resting lymphocytes. The immunophenotypic profile of CLL cells typically includes positivity for CD5 and CD23, along with low expression of CD20 and CD22. The histopathological examination findings of lymph node effacement by small, mature-appearing lymphoid cells are also consistent with CLL.

## **Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because, although it might represent a type of lymphoma, the specific details provided (e.g., CD5 and CD23 positivity) do not align with other common lymphomas like **Diffuse Large B-Cell Lymphoma (DLBCL)**, which typically presents with a more aggressive clinical course and different immunophenotypic markers.
* **Option B:** This option is incorrect as it does not specify a diagnosis; thus, it cannot be evaluated based on the provided clinical and pathological information.
* **Option C:** This option is incorrect because **Mantle Cell Lymphoma (MCL)** typically presents with a different immunophenotypic profile (CD5 positive but CD23 negative) and often has a more aggressive clinical course than CLL.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl in this case is that **CLL often presents with lymphocytosis, lymphadenopathy, and systemic symptoms** like generalized weakness. The presence of **CD5-positive B-cells** narrows the differential diagnosis to CLL and MCL, but **CD23 positivity** is more specific for CLL. This distinction is crucial for prognosis and management.

## **Correct Answer:** D. **Chronic Lymphocytic Leukemia (CLL)**

✓ Correct Answer: C. Chronic lymphocytic leukemia (CLL)