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Difficulty: MediumInterpreting Imaging Results

A 68-year-old man is evaluated in the hospital for a 3-week history of progressively worsening lower back pain. The pain is continuous, wakes him up at night, and is not relieved by rest or over-the-counter analgesics. He also reports intermittent chills. Medical history includes type 2 diabetes mellitus and a recent hospitalization one month ago for a complicated urinary tract infection. Temperature is 38.2°C (100.8°F), blood pressure is 130/80 mmHg, pulse is 92/min, and respiratory rate is 16/min. Physical examination reveals focal tenderness to percussion over the lower lumbar spine. Neurological examination of the lower extremities shows full strength, intact sensation, and normal deep tendon reflexes. Laboratory studies show an erythrocyte sedimentation rate of 85 mm/h and C-reactive protein of 45 mg/L. Blood cultures are drawn. Magnetic resonance imaging (MRI) of the lumbar spine with and without gadolinium contrast reveals decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images involving the L4 and L5 vertebral bodies. There is destruction of the intervening L4-L5 intervertebral disc with enhancement of the disc space and adjacent vertebral endplates. No epidural fluid collection or spinal cord compression is visualized.

Based on the interpretation of these imaging findings, which of the following is the most appropriate next step in management?

  1. CT-guided needle biopsy of the affected intervertebral disc and boneAnswer
  2. B
    Immediate administration of broad-spectrum intravenous antibiotics
  3. C
    Urgent surgical decompression and debridement
  4. D
    Measurement of serum prostate-specific antigen and testosterone levels
  5. E
    Repeating the MRI of the lumbar spine in 4 to 6 weeks

Answer

The most appropriate next step is a CT-guided needle biopsy of the affected intervertebral disc and bone.
The patient's clinical presentation (back pain, fever, focal tenderness) and laboratory findings (elevated inflammatory markers) are highly suggestive of vertebral osteomyelitis and discitis. The MRI findings of T1 hypointensity, T2 hyperintensity in adjacent vertebral bodies, and characteristic destruction of the intervening intervertebral disc confirm this diagnosis. In adults, the intervertebral disc is avascular, so infections originating in the vertebral endplates cross into and destroy the disc space. Because the patient is hemodynamically stable and lacks neurological deficits (the MRI explicitly shows no epidural abscess or cord compression), the most appropriate next step is a CT-guided needle biopsy of the disc space and bone. This provides a definitive microbiological diagnosis to guide targeted, long-term antimicrobial therapy. Administering antibiotics prior to this biopsy can sterilize the bone cultures and prevent identification of the causative organism.

Step-by-Step Solution

1
Analyze the clinical presentation
The patient has back pain, fever, focal spinal tenderness, elevated inflammatory markers, and a recent history of a urinary tract infection.
To establish a pre-test probability for an infectious etiology like vertebral osteomyelitis.
2
Interpret the MRI findings
The MRI shows L4-L5 vertebral body involvement with destruction and enhancement of the intervening intervertebral disc, without epidural abscess or cord compression.
To differentiate between infection (which crosses and destroys the avascular disc space) and malignancy (which typically spares the disc space).
3
Determine the optimal management sequence based on imaging and clinical stability
Because the patient is neurologically intact and hemodynamically stable, tissue biopsy must be obtained before starting antibiotics.
To maximize the yield of microbiological cultures, ensuring the correct targeted, long-term antibiotic therapy can be selected.

Key Concept

In patients with MRI findings of vertebral osteomyelitis and discitis who are hemodynamically stable and neurologically intact, image-guided biopsy of the lesion should be performed prior to initiating empiric antibiotics to ensure accurate microbiological diagnosis.
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Interpreting Imaging Results

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