‘Hairy cell leukemia’ is a neoplastic proliferation of-
**Core Concept**
Hairy cell leukemia is a rare, chronic, and malignant neoplastic disorder characterized by the proliferation of abnormal lymphocytes in the bone marrow, spleen, and liver. The disease is marked by the presence of distinctive "hairy" cells, which are identified by their unique morphology and immunophenotype.
**Why the Correct Answer is Right**
The correct answer is based on the pathophysiology of hairy cell leukemia, which is a type of B-cell lymphoproliferative disorder. The disease is characterized by the accumulation of abnormal B cells, which are mature but functionally incompetent. These cells express surface markers such as CD103, CD25, and CD22, and are often associated with a poor prognosis. The exact cause of hairy cell leukemia is unknown, but it is thought to result from a combination of genetic and environmental factors.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because hairy cell leukemia is not primarily a disorder of T cells, which are a different type of lymphocyte.
* **Option B:** This option is incorrect because chronic lymphocytic leukemia (CLL) is a distinct type of lymphoproliferative disorder that is characterized by the accumulation of mature B cells in the blood and bone marrow, but it does not typically present with the distinctive "hairy" cells seen in hairy cell leukemia.
* **Option C:** This option is incorrect because multiple myeloma is a type of plasma cell malignancy that is characterized by the accumulation of abnormal plasma cells in the bone marrow, but it does not typically present with the "hairy" cells seen in hairy cell leukemia.
**Clinical Pearl / High-Yield Fact**
One important clinical correlation to remember is that hairy cell leukemia is often associated with a deficiency in splenic function, which can lead to a range of symptoms including splenomegaly, anemia, and thrombocytopenia.
**Correct Answer: B. Chronic lymphocytic leukemia.