Osteomyelitis

Osteomyelitis is an infection of the bone acquired hematogenously or by contiguous site infection. In children, hematogenous spread is more common, and the long bones are more often infected. In adults, hematogenously seeded osteomyelitis is seen; however, extension from contiguous sites is more likely. Diabetic foot ulcers and pressure sores are common predisposing conditions.

Diagnosis

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 (Infectious Diseases Society of America [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

Differential Diagnosis

Monitoring

  • C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
    • Recommended after 4 weeks of antimicrobial therapy for vertebral osteomyelitis to evaluate response (IDSA, 2015)
    • CRP likely as effective alone

Background

Epidemiology

  • Incidence (Kremers, 2015)
    • 21.8/100,000 person-years (U.S. adults)
    • 8.8/100,000 (U.S. children)
  • Sex – M>F
    • Children – more than 50% occur in children <5 years
    • Adults – incidence increases with age 

Risk Factors

  • Children
    • Blunt trauma
    • Postoperative
  • Adults
    • Peripheral vascular disease
    • Diabetes mellitus
    • Renal or hepatic failure
    • Immunosuppression
    • Malignancy
    • Neuropathy
    • Intravenous drug use
    • Trauma
    • Surgery – particularly prosthetic implants

Organisms

  • Most common organism
  • Diabetes mellitus, peripheral vascular disease
    • Streptococcus spp
    • Coagulase-positive and -negative Staphylococcus spp
    • Enterococcus spp
    • Anaerobic spp, often polymicrobial
  • Intravenous drug use
    • Pseudomonas aeruginosa
  • Infants and children
  • Neonates
  • Hemoglobinopathies
    • Salmonella spp
  • Uncommon pathogens
    • Fungal and mycobacterial pathogens

Clinical Presentation

  • Constitutional – fever, nonspecific pain
  • Soft-tissue inflammation overlying area of osteomyelitis
  • Open and nonhealing wound over area of bone
  • Vertebral disease – may present with severe back pain
  • Children
    • Limping, reluctance to walk
    • Fever
    • Focal tenderness
    • Swelling

ARUP Lab Tests

Initial test for differentiating bacterial from viral infection

Preferred test to detect acute phase inflammation (eg, autoimmune diseases, connective tissue disease, rheumatoid arthritis, infection, or sepsis)

Nonspecific test used to detect inflammation associated with infections, cancers, and autoimmune diseases

Detect presence of bacteria in blood

Important informationLimited to University of Utah Health Sciences Center only

If anaerobic infection is suspected, send specimen under anaerobic conditions

Related Tests

Detect Bartonella spp in blood, cerebrospinal fluid (CSF), or tissue

Medical Experts

Contributor

Fisher

Mark A. Fisher, PhD, D(ABMM)

Associate Professor of Clinical Pathology, University of Utah

Medical Director, Bacteriology, and Special Microbiology, Antimicrobial Susceptibility Testing, at ARUP Laboratories

Contributor

Genzen

Jonathan R. Genzen, MD, PhD

Associate Professor of Clinical Pathology, University of Utah

Chief Operations Officer, Medical Director of Automated Core Laboratory and Farmington Health Center Clinical Laboratory, at ARUP Laboratories

References

Additional Resources