A 64-year-old man comes to the emergency department after developing fever and chills during hemodialysis. He still feels feverish but has no sore throat, cough, abdominal pain, nausea, or diarrhea. Temperature was 38.9 C (102 F) at the dialysis center. The patient has a history of poorly controlled type 2 diabetes mellitus and hypertension, which led to end-stage renal disease. He was initiated on long-term intermittent hemodialysis 2 months ago. The patient has no known drug allergies. He does not use tobacco, alcohol, or illicit drugs. Temperature is 38 C (100.4 F), blood pressure is 120/62 mm Hg, pulse is 105/min, and respirations are 22/min. Oxygen saturation is 96% on room air. There is a tunneled central venous catheter in the right internal jugular vein, and the skin around the insertion site is not erythematous or tender. Cardiopulmonary auscultation reveals clear lung fields and normal heart sounds. The abdomen is soft and nontender. No skin rash or neck stiffness is present. Leukocyte count is 14,000/mm³ with 90% neutrophils. Chest-x ray reveals no infiltrate or consolidation. Two sets of blood cultures, one from a peripheral vein and the other from the central venous catheter, are obtained. Both sets of blood cultures grow methicillin-resistant Staphylococcus aureus. The patient's antibiotic regimen is narrowed to vancomycin alone, and the tunneled catheter is removed. On day 4 of hospitalization, he continues to have intermittent fevers. He has no cough, abdominal pain, or diarrhea but does note worsening back pain in his lumbar region, which he attributes to inactivity and the uncomfortable hospital bed. The pain is a dull ache and does not radiate. Examination reveals midline tenderness in the lower lumbar area. Neurological examination shows no abnormalities. Leukocyte count remains elevated at 16,000/mm³. Repeat blood cultures performed after venous catheter removal show no growth. Plain radiographs of the lumbosacral spine reveal no abnormalities. Echocardiography reveals no valvular vegetations. Which of the following is the most appropriate next step in management of this patient?

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Explanation: Up to 40% of patients with Staphylococcus aureus bacteremia develop metastatic infection. Risk is greatest in those with community-acquired infections, treatment delays, and persistent bacteremia or fevers. The heart valves, lungs, and osteoarticular structures are most commonly affected. This patient's persistent fever, continued leukocytosis, and worsening lower back pain raise suspicion for a metastatic infection of the spine (eg, vertebral osteomyelitis, epidural abscess). The major manifestation is slowly worsening pain in the back or neck that localizes to the affected disc space. Fever and leukocytosis may or may not be present, and blood cultures are positive in only 50% of cases. Patients with vertebral osteomyelitis often have normal plain radiographs during the first 2 weeks of infection; therefore, this study cannot be used to rule out early osteomyelitis. The diagnostic test of choice is MRI of the spine, which has high sensitivity and specificity and typically detects osteomyelitis within days of initial infection. Confirmation then requires an open or CT-guided biopsy. (Choice A) This patient with known S aureus bacteremia is far more likely to have a metastatic infection with this organism than a new infection or an untreated polymicrobial infection. Prolonged vancomycin therapy (eg, months) is typically required, and this patient's limited response to 4 days of vancomycin is not unusual, although it may raise suspicion for an abscess (eg, spinal epidural), which may require drainage for resolution. MRI of the spine should be ordered to evaluate the back pain prior to the consideration of altering the antibiotic regimen. (Choice B) The evaluation of an occult infection may include CT scans of the chest, abdomen, and pelvis. However, this patient has localizing symptoms to the lumbar spine and should receive a spinal MRI prior to considering other testing. (Choice D) Tagged white blood cell scans are rarely used to diagnose osteomyelitis as findings are generally nonspecific. Other nuclear medicine tests such as PET or gallium imaging are more sensitive and specific but are typically reserved for those with equivocal results on CT scan and plain radiograph who cannot undergo MRI. (Choice E) Vasculitis testing is often performed for patients with fever of unknown origin. This patient with known S aureus bacteremia and a localizing symptom to the spine is far more likely to have osteomyelitis than vasculitis. Educational objective: Patients with Staphylococcus aureus bacteremia often develop metastatic infections of the heart valves, lungs, or osteoarticular structures. Suspicion should be raised in those with continued fever, leukocytosis, or new focal symptoms. Vertebral osteomyelitis is a common complication of S aureus bacteremia and typically presents with back or neck pain. Diagnosis is generally made by MRI of the spine and is confirmed with an open or CT-guided biopsy.

A 64-Year-Old Man Comes to the Emergency Department After Developing