Review Question - QID 104913

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Osteomyelitis Studies Biopsy and culture QID: 104913 (M2.OR.14.28)

QID 104913 (Type "104913" in App Search)

A 45-year-old woman with a history of diabetes presents with 1 week of progressively worsening back pain and subjective fevers. Six months ago, she was treated for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, thought to be secondary to an infected diabetic foot ulcer. There was no inciting trauma for the back pain, and she has no urinary incontinence or altered sensation in her back or legs. Her temperature is 101.3°F (38.5°C), blood pressure is 157/99 mm Hg, pulse is 100/min, respirations are 17/min, and oxygen saturation is 98% on room air. She has point tenderness in her back at the L4 level but no apparent swelling or overlying erythema. Her left foot has the findings depicted in Figure A. Which of the following is the most accurate test for this patient's back pain?

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Biopsy

1/40

0/40

MRI

20%

8/40

Radiograph

60%

24/40

Ultrasound

15%

6/40

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This patient most likely has vertebral osteomyelitis given her fever, focal back pain, immunosuppression (diabetes), and foot ulcer (infection source). The most accurate test for osteomyelitis is a biopsy.

Vertebral osteomyelitis is a bone infection of the vertebrae. Infection typically occurs via hematogenous seeding and most commonly involves the lumbar vertebrae. Patients with diabetes, vascular insufficiency, IV drug use, or superficial skin or soft tissue infections are at increased risk for vertebral osteomyelitis. The best initial test for focal back pain with a fever is often an MRI as this test is needed to rule out osteomyelitis, discitis, or an epidural abscess (however, starting with a CT scan may be reasonable if it is unclear if the pain is of an infectious etiology and suspicion is for trauma/fracture). The most accurate test for osteomyelitis is a biopsy which can confirm the diagnosis and organism thus guiding antibiotic therapy.

Figure A demonstrates a diabetic foot ulcer which is a likely source of infection for this patient's osteomyelitis.

Incorrect Answers
Answer 2: CT is typically reserved for imaging when there are focal spinal tenderness and a concern for a fracture. However, fever and back pain in an immunosuppressed patient is concerning for discitis, osteomyelitis, or an epidural abscess thus warranting an initial MRI. This would not be the most accurate test for osteomyelitis.

Answer 3: MRI is the most accurate imaging test for osteomyelitis and has the highest sensitivity/specificity (when compared to other imaging tests); however, biopsy still remains the most accurate test.

Answer 5: Radiographs are almost never the most accurate test as they lack sufficient detail to confirm a diagnosis. Radiographs are a specific but non-sensitive test for osteomyelitis.

Answer 5: Ultrasound is not indicated to diagnose osteomyelitis but could be indicated to diagnose abscess or cellulitis.

Bullet Summary:
The most accurate test for osteomyelitis is a biopsy.

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