**Question:** In multiple myeloma there is proliferation of -

A. Plasma cells
B. Red blood cells
C. White blood cells
D. Neurons

**Core Concept:**
Multiple myeloma is a plasma cell disorder characterized by the proliferation and accumulation of malignant plasma cells in the bone marrow. Plasma cells are a type of white blood cell, specifically B lymphocytes that mature into antibody-producing cells in response to an antigen. In multiple myeloma, these cells undergo uncontrolled proliferation, leading to bone marrow failure, and the production of monoclonal proteins (M proteins), which can cause symptoms and complications.

**Why the Correct Answer is Right:**
In multiple myeloma, plasma cells (A) are the target of proliferation due to the abnormal B-cell differentiation and clonal expansion. This leads to the accumulation of these abnormal plasma cells in the bone marrow, interfering with normal hematopoiesis and resulting in the production of M proteins (B) that can cause organ damage and clinical manifestations.

**Why Each Wrong Option is Incorrect:**

B. Red blood cells (C) are not involved in multiple myeloma, as the disease primarily affects plasma cells and not erythropoiesis.

C. White blood cells (C) are not the correct answer because multiple myeloma primarily involves plasma cells, not other types of white blood cells.

D. Neurons (D) are not affected in multiple myeloma as the disease primarily involves the bone marrow, affecting plasma cells and their production of monoclonal proteins.

**Clinical Pearl:**
Multiple myeloma is a complex disease with diverse clinical presentations, often associated with bone lesions, renal dysfunction, anemia, and hypercalcemia. Early detection and treatment are crucial to improve patient outcomes as the disease can lead to life-threatening complications.