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Difficulty: MediumDiagnostic Workup and Test Sequencing

An office worker in his late 60s is evaluated in the clinic for three months of non-radiating, deep lower back pain and progressive generalized fatigue. He reports that his pain is worse with movement and has not responded to escalating doses of over-the-counter ibuprofen. He denies fevers, weight loss, or urinary incontinence. His past medical history is notable only for mild osteoarthritis. Vital signs are within normal limits. Physical examination demonstrates marked conjunctival pallor and localized tenderness to palpation over the L3 and L4 spinous processes. Neurological examination, including strength, sensation, and deep tendon reflexes in the lower extremities, is unremarkable. Initial laboratory analysis reveals the following:

* Hemoglobin: 9.4 g/dL
* Mean corpuscular volume: 89 fL
* Leukocyte count: 5,500/mm³
* Platelet count: 165,000/mm³
* Creatinine: 1.8 mg/dL
* Calcium: 11.4 mg/dL

Which of the following diagnostic studies should be ordered concurrently as the most appropriate next steps in this patient's evaluation? (Select three)

  1. Serum and urine protein electrophoresis with immunofixationAnswer
  2. Serum free light chain assayAnswer
  3. Whole-body low-dose computed tomographyAnswer
  4. D
    Technetium-99m radionuclide bone scintigraphy
  5. E
    Bone marrow aspiration and biopsy
  6. F
    Magnetic resonance imaging of the lumbar spine

Answer

The most appropriate concurrent next steps in this patient's evaluation are serum and urine protein electrophoresis with immunofixation, serum free light chain assay, and whole-body low-dose computed tomography.
This patient presents with the classic 'CRAB' manifestations of multiple myeloma: hypercalcemia, renal insufficiency, anemia, and bone pain (localized to the lumbar spine). The initial diagnostic workup must achieve two goals simultaneously: detecting the underlying plasma cell dyscrasia and evaluating the extent of bone involvement. Current guidelines mandate a concurrent initial panel consisting of serum and urine protein electrophoresis with immunofixation to identify a monoclonal protein (M-spike), a serum free light chain assay to detect light-chain predominant disease, and a whole-body low-dose computed tomography (WBLDCT) scan. WBLDCT has largely replaced the conventional skeletal survey due to its superior sensitivity for detecting osteolytic lesions and impending fractures.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and laboratory findings.
The patient exhibits hypercalcemia, renal insufficiency, normocytic anemia, and bone pain (CRAB criteria).
Identifying the classic CRAB tetrad strongly suggests a diagnosis of multiple myeloma.
2
Determine the initial, non-invasive diagnostic tests required to screen for a plasma cell dyscrasia.
Identify the need for serum/urine protein electrophoresis with immunofixation and a serum free light chain assay.
These concurrent laboratory tests provide a highly sensitive screening panel to detect circulating monoclonal proteins or free light chains.
3
Select the most appropriate initial imaging modality to evaluate for skeletal involvement.
Select whole-body low-dose computed tomography (WBLDCT).
WBLDCT is the current standard-of-care initial imaging test to detect the purely osteoclastic lytic lesions characteristic of multiple myeloma.

Key Concept

The initial diagnostic workup for suspected multiple myeloma requires concurrent testing for monoclonal proteins (using SPEP/UPEP and serum free light chains) and systemic evaluation for osteolytic bone lesions (using whole-body low-dose CT).
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Diagnostic Workup and Test Sequencing

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