CORE EM: Vertebral Osteomyelitis

Definition

• Inflammation of the vertebrae due to a pyogenic, fungal or mycobacterial organism.

  

• Classified as either acute (days), subacute (weeks) or chronic (months)
• Spondylodiscitis: a term encompassing osteomyelitis, spondylitis and discitis. Often used interchangeably with osteomyelitis.

Epidemiology

• 1 to 2.4 cases per 100,000 people (Zimmerli 2010)
• More common in males with M:F of 3:1
• Rate is also increasing due to increased number of spinal procedures
• Typically affects adults, with most cases occurring in patients over 50 years old.

Pathogenesis

• Infection occurs by three routes:
  • Hematogenous spread – secondary to infections of the GU, skin, soft tissue and respiratory system, indwelling catheters or endocarditis
    • Due to the bifurcated structure of the arterial supply, generally presents as infection of 2 contiguous vertebrae and the intervertebral disc
  • Direct inoculation during trauma or spinal surgery
  • Spread from adjacent soft tissue infection
• Organism
  • Most cases in the United States are pyogenic.
    • Most common organism is Staph Aureus (36-67% of cases) (Boody 2015).
    • Other pathogens include: E. Coli, Pseudomonas Aeruginosa and Group B and G hemolytic Strep
  • Other pathogens to consider:
    • Fungal – blastomycosis, coccidiomycosis, histoplasmosis, aspergillosis
    • Brucellosis
    • Mycobacterial
  • Location: lumbar (48%) most common, followed by thoracic (35%) and cervical (6.5%)

History and Physical

• Risk Factors:
  • Diabetes Mellitus (most common)
  • Immunosuppression: HIV, Malignancy, chronic steroids or immunosuppressant medication use
  • Spinal fracture, trauma or recent procedure
  • Substance Abuse: Alcoholism and IVDU
  • Presence of an indwelling vascular device
  • Elderly
•  Symptoms
  • Back pain – often described as dull, may be present for weeks to months
  • Neurologic symptoms (paresthesias, weakness or radiculopathy) present in approximately one-third of patients
  • Most patients lack systemic symptoms
• Exam
  • Tenderness over affected vertebrae
  • Paraspinal tenderness or spams may be present which may mislead the clinician towards a musculoskeletal diagnoses

Diagnostics

• Labs
  • Leukocytosis and Neutrophilia are poorly sensitive and highly non-specific (Gouliouris 2010). The degree of elevation does not predict disease severity.
  • ESR and CRP are sensitive, yet not specific.
    • CRP concentration rise and fall quicker than ESR, often used to guide treatment
  • Blood Cultures – an important element in management and treatment
    • Blood culture positivity often decides whether a patient will require a bone biopsy.
    • Cultured specimen narrows antibiotic coverage
  • Urinalysis/Urine Culture –UTI is a frequent missed source of bacteremia (especially in diabetic patients).
• Imaging
  

  MRI Images – mghradrounds.org

  • Gadolinium enhanced MRI – modality of choice, highly sensitive and specific (Mylona 2009).
    • Although MRI with and without contrast is preferred, a non-contrast MRI can evaluate for inflammatory processes.
    • If a patient requires premedication or has renal failure, obtain the non-contrast MRI first. A contrast MRI can be done later to delineate subtle findings.
    • Findings include: enhancement (hypointense on T1 and hyperintense on T2) of vertebral endplates and adjacent disc space (Image 1)
  • CT Scan with IV contrast – use only if MRI contraindicated
    • Inferior in evaluation of disc spaces and neural tissues
      • Less sensitive than MRI and may be falsely negative in early disease
      • Used primarily by surgeons for biopsy of spine
    • Findings include loss of end plate definition and narrowing of disc space (Image 2)
    • Previously used CT Myelogram now out of favor due to potential for intradural spread of infection.
  • Plain Radiographs – often done to evaluate other causes (masses, fracture) however not recommended for diagnosis
    • Poorly sensitive and findings typically present in advanced disease (10-14 days after onset), once significant bone demineralization has already occurred
  • Radionuclide studies – (including: Tech 99m Bone scan, Gallium -67)
  • Sensitive but not specific, long acquisition time and difficult to obtain in the emergent setting

Management

• Pathogen directed therapy – Antibiotics tailored towards cultured organism
  • Given the dependence on blood culture results to guide therapy, current recommendations (IDSA 2015 Guidelines) suggest holding empiric antibiotics in medically stable patients (non-septic, hemodynamically stable, neurologically intact) until cultures grow out.
    • Note: this is a weak recommendation based on low quality evidence and patients should be managed on a case by case basis in conjunction with the inpatient treatment team
  • Empiric coverage:
    • Vancomycin 15-20 mg/kg/dose every 8-12 hrs PLUS
    • 3^rd Generation Cephalosporin: Cefotaxime (2 g IV every 6 hrs), Ceftriaxone (1 to 2 g IV daily) or Ceftazidime (1 to 2 g IV every 8 -12 hrs)
    • Alternate: Cefepime 2 g IV every 12 hours
    • Duration: 6 weeks (occasionally 12 weeks if advanced disease) of IV antibiotics followed by 1-2 months of oral antibiotics

• Surgical Consult – although most patients are successfully treated with antibiotics alone, some may require surgical intervention if there is concern for vertebral instability or spinal cord compromise.
  • Indications for surgical intervention include: associated abscess formation, spinal cord compression, progression of disease despite antimicrobial treatment
  • Obtain consult (Neurosurgery or Orthopedics) early, since patients may require bone biopsy for detection of organism

Take Home Points

• Clinical presentation is very nonspecific; evaluate all patients presenting with back pain for infectious risk factors.
• Baseline labs should not guide diagnosis, but may assist in later management.
• MRI is key to diagnosis, obtain this imaging in all patients who raise clinical suspicion
• Patients with hemodynamic instability and neurologic compromise warrant empiric antibiotics. The initiation of empiric antibiotics in hemodynamically stable, neurologically intact patients should be done on a case-by-case basis.

References

Berbari EF, Kanj SS, et al. Executive Summary: 2015 Infectious Disease Society of America (IDSA) Clinical Practice Guidelines for the Diagnosis and Treatment of Native Vertebral Osteomyelitis in Adults. Clin Infect Dis 2015 Sept 15;61(6):859-63. PMID: 26316526

Boody B, et al. Vertebral Osteomyelitis and Spinal Epidural Abscess: An Evidence-based Review. J Spinal Disord Tech. 2015 Jul;28(6):E316-27 PMID: 26079841

Chowdhury V, Gupta A, Khandelwal N. Diagnostic Radiology: Musculoskeletal and Breast Imaging. 3^rd ed. New Delhi: JP Brothers Medical Ltd; 2012

Della-Guistina, D. Evaluation and Treatment of Acute Back Pain in the Emergency Department. Orthopedic Emergencies 2015 May; 33(2) 311-26. PMID: 25892724

Gouliouris T, et al. Spondylodiscitis: update on diagnosis and management. J Antimicrob Chemother. 2010 Nov;65 Suppl 3:iii 11-24 PMID: 20876624

Mylona E, et al. Pyogenic Vertebral Osteomyelitis: A Systematic Review of Clinical Characteristics. Semin Arthritis Rheum. 2009 Aug; 39(1):10-7. PMID: 18550153

Pruitt CR, Perron AD. Specific Disorders of the Spine. In: Sherman SC eds. Simon’s Emergency Orthopedics. 7^th ed. New York, NY: McGraw-Hill; 2014

Winters ME, Kluetz P et al. Back Pain Emergencies. Med Clin North Am, 2006 May;90(3):505-23. PMID: 16473102

Zimmerli W. Vertebral Osteomyelitis. N Engl J Med 2010 Mar; 362(11)1022-9. PMID: 20237348