A 71-year-old man is evaluated in the clinic for a 3-month history of worsening lower back… — USMLE Step 2 CK

A 71-year-old man is evaluated in the clinic for a 3-month history of worsening lower back pain and generalized fatigue. The pain is deep, achy, and localized to the mid-lumbar region without radiation to the legs. He also reports new-onset constipation and increased frequency of urination. He has no significant past medical history and takes no medications. His temperature is $37.0^\circ\text{C}$ ( $98.6^\circ\text{F}$ ), blood pressure is $142/88$ mmHg, pulse is $84$ /min, and respiratory rate is $14$ /min. Physical examination shows midline point tenderness over the L4 vertebra. Neurologic examination of the lower extremities shows $5/5$ strength with normal deep tendon reflexes.

Laboratory results are as follows:

Laboratory Test	Result
Hemoglobin	$9.1$ g/dL
Leukocytes	$6,800/\text{mm}^3$
Platelets	$210,000/\text{mm}^3$
Blood urea nitrogen	$38$ mg/dL
Serum creatinine	$2.2$ mg/dL
Serum calcium	$11.9$ mg/dL
Total serum protein	$9.2$ g/dL
Serum albumin	$3.5$ g/dL

Which of the following is the most appropriate next step in the diagnostic evaluation of this patient?

A
Intact parathyroid hormone level
B
Measurement of serum prostate-specific antigen
C
Radionuclide bone scan
Serum and urine protein electrophoresisCevap
E
Renal ultrasonography

Cevap

Serum and urine protein electrophoresis

This patient's clinical presentation is highly suspicious for multiple myeloma, characterized by the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lytic lesions). A critical diagnostic clue is the significant protein gap (total serum protein minus serum albumin

> 4

g/dL), which strongly suggests the presence of a circulating monoclonal immunoglobulin (M-protein). The most appropriate initial step to evaluate for a monoclonal gammopathy is serum and urine protein electrophoresis (SPEP and UPEP), often combined with immunofixation. If a monoclonal spike is detected, a bone marrow biopsy is subsequently performed to confirm the diagnosis.

Adım Adım Çözüm

Analyze the clinical presentation and physical examination.

An elderly man presents with progressive lower back pain, bony tenderness, fatigue, polyuria, and constipation.

To identify key symptoms that suggest a systemic oncologic or endocrine condition rather than isolated mechanical back pain.

Evaluate the laboratory panel for specific diagnostic clues.

The patient has anemia, acute kidney injury (elevated BUN/creatinine), severe hypercalcemia, and a massive protein gap (Total protein

9.2

- Albumin

3.5

5.7

g/dL).

To synthesize the findings into a unifying diagnosis, recognizing the classic CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lesions) of multiple myeloma.

Determine the most appropriate initial diagnostic test.

The constellation of findings is highly suspicious for multiple myeloma. The initial test of choice to identify the underlying monoclonal gammopathy is serum and urine protein electrophoresis.

To confirm the presence of an M-spike (monoclonal protein) before proceeding to definitive bone marrow biopsy.

Anahtar Kavram

The classic presentation of multiple myeloma includes the CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lytic lesions) alongside a significant protein gap (>4 g/dL). Initial diagnosis requires identification of a monoclonal protein using serum and urine protein electrophoresis.

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