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Difficulty: MediumNeoplastic Processes

An evaluation of a 6868-year-old retired mechanic is prompted by a 33-month history of severe, non-radiating mid-back pain and progressive fatigue. He reports no recent trauma but notes he has been increasingly constipated and urinating more frequently than usual. Vital signs are within normal limits. Physical examination reveals point tenderness over the L 33 and L 44 vertebrae. Laboratory investigations demonstrate a hemoglobin of 8.9 g/dL8.9 \text{ g/dL}, serum calcium of 11.6 mg/dL11.6 \text{ mg/dL}, and serum creatinine of 2.1 mg/dL2.1 \text{ mg/dL}. A peripheral blood smear shows red blood cells stacked like coins. Serum protein electrophoresis reveals a sharp monoclonal peak in the gamma region. A subsequent skeletal survey displays multiple punched-out radiolucent lesions in the skull and lumbar spine. Which of the following best describes the primary underlying neoplastic process responsible for this patient's radiologic findings?

  1. Increased expression of receptor activator of nuclear factor kappa-B ligand (RANKL) by clonal plasma cellsAnswer
  2. B
    Ectopic tumor secretion of parathyroid hormone-related peptide (PTHrP) into the systemic circulation
  3. C
    Release of endothelin-1 leading to abnormal, disorganized osteoblastic proliferation
  4. D
    Microvascular thrombosis from tumor-induced hypercoagulability leading to local bone infarctions
  5. E
    Parathyroid hormone elevation driven by tumor-induced acute kidney injury causing secondary bone resorption

Answer

The correct answer is the increased expression of receptor activator of nuclear factor kappa-B ligand (RANKL) by clonal plasma cells.
The correct answer identifies that the skeletal destruction in multiple myeloma is mediated by the neoplastic plasma cells interacting with bone marrow stroma. These malignant cells secrete various cytokines (e.g., MIP-1 α\alpha) that upregulate the expression of receptor activator of nuclear factor kappa-B ligand (RANKL) while concurrently downregulating osteoprotegerin (OPG). This severe imbalance heavily favors osteoclast differentiation and activation, leading to the characteristic 'punched-out' lytic bone lesions and subsequent hypercalcemia seen in this patient.

Step-by-Step Solution

1
Analyze the patient's clinical and laboratory presentation.
The patient exhibits hypercalcemia, renal insufficiency, anemia, and bone lesions (CRAB criteria), along with rouleaux formation and a monoclonal gamma spike.
Synthesizing these findings establishes a primary diagnosis of multiple myeloma, a plasma cell dyscrasia.
2
Examine the specific radiologic findings provided in the stem.
The skeletal survey shows 'punched-out' radiolucent (osteolytic) lesions in the skull and spine.
Identifying the nature of the bone lesions differentiates the neoplastic mechanism from osteoblastic processes (like prostate cancer) or metabolic bone disease.
3
Determine the pathophysiologic mechanism by which multiple myeloma causes osteolytic lesions.
Myeloma cells interact with bone marrow stromal cells to upregulate RANKL and downregulate osteoprotegerin (OPG), leading to rampant osteoclast activation and bone resorption.
This molecular interaction is the fundamental neoplastic process driving the destructive skeletal pathology in multiple myeloma.

Key Concept

In multiple myeloma, neoplastic plasma cells stimulate osteoclast activity and cause lytic bone lesions primarily through the upregulation of receptor activator of nuclear factor kappa-B ligand (RANKL) and the inhibition of osteoblasts.
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Topics

Neoplastic Processes

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