Osteomyelitis

Indications for Testing

• Chronic, nonhealing ulcer that can be probed to the bone (eg, diabetic foot ulcer, decubitus ulcer in immobilized patient)
• Localized bone pain with signs and/or symptoms of infection
• Back pain or neck pain with
  • Fever
  • Elevated C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR)
  • Blood stream infection or infective endocarditis
  • Recent Staphylococcus aureus bacteremia
• New neurological symptoms with or without back pain or neck pain

Laboratory Testing

• CBC
  • May be normal or show leukocytosis or left shift
  • Leukocyte count may be normal in chronic or indolent osteomyelitis
  • Normocytic normochromic anemia may be present if infection is chronic (anemia of chronic inflammation)
• CRP
  • Preferred test to detect acute inflammation (Choosing Wisely, American Society for Clinical Pathology, 2016)
  • Emerging as preferred marker for diagnosis and monitoring of osteomyelitis
  • Frequently elevated but not specific
  • Normal ESR and CRP essentially rule out osteomyelitis
  • Specific types
    • Vertebral osteomyelitis – use CRP in conjunction with ESR in all patients with clinical signs (IDSA, 2015)
    • Diabetic foot osteomyelitis – use CRP with ESR in conjunction with white blood cell (WBC) count to assess severity of infection of ulcer (IDSA, 2012)
• ESR (sed rate, Westergren sedimentation rate) – order if CRP not available
  • Marker of inflammation – increases and decreases more slowly than CRP
  • Diabetic foot osteomyelitis – ulcer depth >3 mm and ESR >60 mm/hr assist in differentiation of cellulitis from osteomyelitis (IDSA, 2012)
• Routine blood culture
  • Collect prior to antibiotic administration in all suspected cases
  • ≥2 sets of cultures (aerobic and anaerobic) should be obtained from different draws (IDSA, 2015)
  • Positive cultures may preclude need for bone biopsy
  • Positive in up to half of cases
• Tissue culture
  • Superficial culture not useful
  • Bone sample necessary unless organism identified in blood
  • Bone or deep tissue obtained at debridement, or imaging-guided or surgical biopsy/aspirate
• Procalcitonin
  • Use in conjunction with other inflammatory markers (acute phase reactant)
  • Elevated in severe bacterial disease (eg, sepsis)
  • Being evaluated as assessment of osteomyelitis disease severity
• Other organism testing for vertebral osteomyelitis (rare organisms)
  • Test if risk factors or epidemiology appropriate or after no growth of bacterial cultures
  • Blood cultures and serologic tests for Brucella recommended for patients with vertebral osteomyelitis in endemic areas
  • Obtain fungal cultures if patient is at risk for fungal vertebral osteomyelitis due to risk factors or epidemiologic factors
  • Purified protein derivative (PPD) or interferon – gamma release assay for mycobacterium tuberculosis (TB) for at-risk patients
• Polymerase chain reaction (PCR)
  • Not widely available; may be useful if all cultures are negative
  • Most useful for Bartonella henselae and Kingella kingae

Imaging Studies

• Criteria for diagnosis
  • American College of Radiology (ACR) Appropriateness Criteria outline recommendations for imaging for suspected osteomyelitis in diabetic foot ulcers
• Imaging modalities for osteomyelitis
  • Plain x-ray films – may not demonstrate presence of osteomyelitis until 10-14 days after infection is established
    • Negative film does not rule out diagnosis
    • Evidence for osteomyelitis on film – periosteal lifting or lytic lesions
  • Magnetic resonance imaging (MRI) – indicated after x-ray or in combination to identify extent of disease
  • Labeled leukocyte bone scan – indicated in absence of MRI
  • Computerized tomography (CT) scan – not as sensitive as MRI; not useful if metal is near the infection 

Differential Diagnosis

• Arthritis
  • Septic
  • Degenerative
  • Crystalline
  • Reactive
• Juvenile rheumatoid arthritis
• Neuropathic disease
• Metastatic bone disease
• Paget disease