A 62-year-old man is brought to the emergency department with four days of progressively w… — USMLE Step 3

A $62$ -year-old man is brought to the emergency department with four days of progressively worsening back pain and low-grade fevers. He reports that over the past $12$ hours, he has developed weakness in both legs and has been unable to urinate. Two weeks ago, he was treated for a cutaneous abscess on his left thigh. His temperature is $38.3^\circ\text{C}$ ( $100.9^\circ\text{F}$ ), blood pressure is $135/85 \text{ mmHg}$ , and heart rate is $102 \text{ /min}$ . Neurologic examination reveals $3/5$ strength in the bilateral lower extremities, decreased sensation to pinprick below the umbilicus, and decreased rectal sphincter tone. There is exquisite focal percussion tenderness over the T10 spinous process. Laboratory studies reveal a serum creatinine of $1.6 \text{ mg/dL}$ (estimated glomerular filtration rate: $45 \text{ mL/min/1.73 m}^2$ ). He has no implanted medical devices. Which of the following diagnostic studies are appropriate NEXT steps in the workup of this patient? (Select all that apply)

Magnetic resonance imaging of the spine with intravenous gadolinium contrastAnswer
Two sets of peripheral blood culturesAnswer
C
Lumbar puncture for cerebrospinal fluid analysis
D
Plain radiography of the thoracic spine
E
Computed tomography myelography

Answer

The appropriate next steps are magnetic resonance imaging of the spine with intravenous gadolinium contrast, and obtaining two sets of peripheral blood cultures.

This patient's presentation of fever, severe back pain, and acute lower extremity neurologic deficits (weakness, bowel/bladder dysfunction, sensory level) following a recent skin infection is highly suspicious for a spinal epidural abscess (SEA). SEA is a neurologic emergency. The immediate diagnostic sequence requires delineating the anatomic extent of cord compression and identifying the pathogen. Magnetic resonance imaging (MRI) of the spine with intravenous gadolinium contrast is the imaging modality of choice due to its superior visualization of the epidural space and spinal cord. While an eGFR of 45 mL/min/1.73 m^2 represents moderate chronic kidney disease, it is not a contraindication to gadolinium in an emergency context; the risk of permanent paralysis heavily outweighs the low risk of nephrogenic systemic fibrosis with modern gadolinium agents. Concurrently, obtaining two sets of peripheral blood cultures is mandatory before initiating empiric antimicrobial therapy, as bacteremia is present in most SEA cases and identifying the pathogen is crucial for tailoring prolonged antibiotic therapy.

Step-by-Step Solution

Identify the clinical syndrome from the patient's presentation.

The patient presents with the classic triad of a spinal epidural abscess (SEA): fever, localized back pain, and neurologic deficits (paraparesis, urinary retention, sensory level).

Recognizing this neurologic emergency dictates the urgency and specific type of diagnostic workup required.

Determine the preferred definitive imaging modality.

Magnetic resonance imaging (MRI) of the spine with gadolinium contrast is the gold standard for diagnosing SEA.

It provides the highest sensitivity and specificity for delineating the epidural mass and evaluating the degree of spinal cord compression.

Assess potential contraindications to the preferred imaging.

The patient has an eGFR of 45 mL/min/1.73 m^2. This moderate chronic kidney disease is not an absolute contraindication to gadolinium.

In the setting of a life-threatening neurologic emergency, the risk of permanent paralysis from an undiagnosed SEA far outweighs the theoretical risk of nephrogenic systemic fibrosis, especially with modern Group II gadolinium agents.

Select the appropriate concurrent laboratory diagnostic step.

Peripheral blood cultures should be drawn concurrently with expediting the MRI.

Identifying the causative organism (most commonly Staphylococcus aureus) is critical for targeted long-term antibiotic therapy. Cultures must ideally be obtained prior to initiating empiric antibiotics.

Key Concept

Patients with suspected spinal epidural abscess and acute neurologic compromise require immediate MRI of the spine with gadolinium contrast and concurrent peripheral blood cultures prior to empiric antibiotic administration.

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