A 71-year-old man comes to the clinic for a 4-month history of progressive lower back pain… — USMLE Step 2 CK

A 71-year-old man comes to the clinic for a 4-month history of progressive lower back pain and severe fatigue. He states that the pain is a constant, deep ache that does not improve with rest or over-the-counter ibuprofen. Over the same period, he has developed increasing constipation. He has no prior medical history and takes no daily medications. Vital signs are within normal limits. Physical examination reveals generalized pallor and localized tenderness to palpation over the mid-lumbar spine. Neurologic examination is unremarkable. Laboratory studies show the following:

Test	Result	Reference Range
Hemoglobin	8.9 g/dL	13.5–17.5 g/dL
Mean corpuscular volume	89 fL	80–100 fL
Leukocyte count	6,200/mm³	4,500–11,000/mm³
Platelet count	195,000/mm³	150,000–400,000/mm³
Blood urea nitrogen	34 mg/dL	8–20 mg/dL
Serum creatinine	2.3 mg/dL	0.7–1.3 mg/dL
Serum calcium	11.9 mg/dL	8.4–10.2 mg/dL
Total serum protein	9.1 g/dL	6.0–7.8 g/dL
Serum albumin	3.4 g/dL	3.5–5.5 g/dL

Which of the following is the most appropriate next step in establishing the diagnosis?

A
Measurement of intact parathyroid hormone
B
Prostate-specific antigen testing
C
Radionuclide bone scan
D
Renal ultrasonography
Serum and urine protein electrophoresisAnswer

Answer

Serum and urine protein electrophoresis

The correct answer is serum and urine protein electrophoresis. This patient's presentation of normocytic anemia, renal insufficiency, hypercalcemia, and bone pain is highly suspicious for multiple myeloma (often remembered by the acronym CRAB). A critical laboratory clue is the elevated protein gap (total serum protein minus serum albumin =

9.1 - 3.4 = 5.7

g/dL). A gap greater than

4.0

g/dL indicates an excess of non-albumin proteins in the blood, which are typically immunoglobulins. The most appropriate initial step to evaluate for a monoclonal gammopathy is serum and urine protein electrophoresis (SPEP/UPEP), which can detect a monoclonal protein spike (M-spike) produced by the neoplastic plasma cells.

Step-by-Step Solution

Identify the patient's core clinical syndrome.

The patient presents with bone pain, normocytic anemia, hypercalcemia, and renal insufficiency.

Recognizing this constellation of symptoms is essential for forming an accurate differential diagnosis.

Analyze the laboratory findings for clues to the underlying etiology.

There is a significantly elevated total protein with a normal-to-low albumin, indicating an elevated 'protein gap' (Total Protein - Albumin

> 4

g/dL).

A large protein gap suggests the presence of an excess of non-albumin proteins in the blood, typically immunoglobulins, pointing toward a monoclonal gammopathy.

Determine the most appropriate diagnostic test for the suspected condition.

The combination of CRAB symptoms (Hypercalcemia, Renal failure, Anemia, Bone pain) and a protein gap strongly suggests multiple myeloma. This is diagnosed initially via serum and urine protein electrophoresis.

Protein electrophoresis detects the monoclonal antibody spike (M-spike) characteristic of multiple myeloma, confirming the underlying plasma cell dyscrasia.

Key Concept

Multiple myeloma classically presents with hypercalcemia, renal insufficiency, anemia, and bone pain (CRAB). An elevated protein gap (total protein minus albumin

> 4

g/dL) is a strong clue for a monoclonal gammopathy, and the essential initial diagnostic step is serum and urine protein electrophoresis.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic