Today, we’re examining a clinical case of a 35-year-old woman in the emergency department who reports three weeks of severe lower back pain that’s worse with movement, as well as chills and intermittent fevers. What’s the likely cause?
A 35-year-old woman presents to the emergency department for three weeks of severe lower back pain that is worse with movement, chills, and intermittent fevers. She has a history of injection drug use. Temperature is 39.2°C (102.6°F), heart rate is 112/min, blood pressure is 120/80 mm Hg, and respiratory rate is 22/min. Physical examination reveals tenderness over the lumbar spine at L3 and a 4/6 holosystolic murmur is best heard at the left sternal border. Neurological examination is within normal limits. Laboratory findings are significant for a white blood cell (WBC) count of 15,500/μL, C-reactive protein (CRP) of 130 mg/L, and an erythrocyte sedimentation rate (ESR) of 120 mm/h. Spine x-rays show L3 vertebral body destruction and collapse of the intervertebral disc space.
Which of the following organisms is the most likely cause of this patient’s condition?
A. Staphylococcus aureus
B. Coxiella burnetii
C. Streptococcus mutans
D. Candida albicans
E. Mycobacterium tuberculosis
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 2 Question is…
A. Staphylococcus aureus
See Main Explanation.
Incorrect Answer Explanations
B. Coxiella burnetii
Incorrect: Coxiella burnetii, the causative agent of Q fever, can lead to endocarditis, primarily in patients with chronic disease or certain occupational exposures like livestock handling. However, Staphylococcus aureus is the most likely cause of osteomyelitis associated with endocarditis.
C. Streptococcus mutans
Incorrect: While Streptococcus mutans is associated with endocarditis, it is not a common cause of osteomyelitis. Staphylococcus aureus is the most likely cause of osteomyelitis associated with endocarditis.
D. Candida albicans
Incorrect: Candida albicans can cause chronic osteomyelitis, primarily in immunocompromised patients or in patients with prolonged central venous access. This patient’s lack of evident immunosuppression and acute presentation make Candida a less likely pathogen. Staphylococcus aureus is the most likely cause of osteomyelitis associated with endocarditis.
E. Mycobacterium tuberculosis
Incorrect: Mycobacterium tuberculosis can cause spinal tuberculosis (Pott’s disease), but it typically presents with a more chronic course. Staphylococcus aureus is the most likely cause of osteomyelitis associated with endocarditis. US guided biopsy should be performed and cultures should test for Mycobacterium tuberculosis to rule it out.
Main Explanation
The patient’s presentation of acute lower back pain and tenderness, fevers and chills, history of intravenous drug use, and x-ray findings suggests acute vertebral osteomyelitis. The presence of a 4/6 holosystolic murmur raises concern for infective endocarditis with bacteremia and hematogenous spread to the vertebral column. Staphylococcus aureus is the most common cause of osteomyelitis in patients who use IV drugs, and it is known for its aggressive nature and propensity to affect bones and heart valves.
Patients with acute osteomyelitis typically exhibit localized pain at the infection site, often accompanied by tenderness, swelling, and warmth. Systemic symptoms such as fevers and chills frequently occur. In chronic osteomyelitis, symptoms can be more subtle and insidious, such as a continuous dull ache or localized discomfort at the site of infection. Intravenous drug use is a risk factor for vertebral osteomyelitis. Patients can present with severe back pain, fever, chills, weight loss, and neurological signs and symptoms such as incontinence or focal neurologic deficits.
Major Takeaway
Staphylococcus aureus is the most common cause of osteomyelitis in general and the most common cause of osteomyelitis in patients who use intravenous drugs. Patients with vertebral osteomyelitis typically present with severe localized back pain and systemic symptoms, with or without neurologic findings.
Want to learn more about this topic?
Watch the Osmosis video: Osteomyelitis: Clinical sciences
References
- Berbari EF, Kanj SS, Kowalski TJ, et al. 2015 Infectious Diseases Society of America (IDSA) Clinical Practice Guidelines for the Diagnosis and Treatment of Native Vertebral Osteomyelitis in Adults. Clin Infect Dis. 2015;61(6):e26-e46. doi:10.1093/cid/civ482
Want more USMLE® Step 2 CK practice questions? Try Osmosis by Elsevier today! Access your free trial and discover why millions of current and future clinicians and caregivers love learning with us.
Leave a Reply