What is the initial workup for a patient suspected of having osteomyelitis?

Initial Workup for Suspected Osteomyelitis

The initial workup for a patient with suspected osteomyelitis should include blood cultures, inflammatory markers (ESR, CRP, and/or procalcitonin), plain radiographs, and MRI as the preferred imaging modality, followed by bone biopsy when diagnosis remains uncertain. 1

Clinical Assessment and Laboratory Studies

• Perform a thorough medical and neurologic examination to identify potential sources of hematogenous seeding and assess motor/sensory function 1
• Obtain two sets of aerobic and anaerobic blood cultures before starting antibiotics 1
• Measure inflammatory markers:
  • C-reactive protein (CRP) 1
  • Erythrocyte sedimentation rate (ESR) 1
  • Procalcitonin (PCT) may be helpful when clinical examination is diagnostically equivocal 1
• Note that inflammatory markers are particularly useful when clinical findings are inconclusive, but white blood cell count is a poor indicator of osteomyelitis 2

Imaging Studies

Initial Imaging

• Plain radiographs should be the first imaging test for all patients with suspected osteomyelitis 1
  • While often not diagnostic in early acute osteomyelitis, they provide anatomic evaluation and can reveal alternative diagnoses 1
  • Classic changes suggestive of osteomyelitis include cortical erosion, periosteal reaction, and mixed lucency and sclerosis 1

Advanced Imaging

• MRI with and without contrast is the preferred imaging modality when diagnosis remains uncertain after initial radiographs 1

  • Has 97% sensitivity, 93% specificity, and 94% accuracy in diagnosing osteomyelitis 1
  • Characteristic findings include decreased T1-weighted bone marrow signal with increased signal on fluid-sensitive sequences 1
  • A normal marrow signal on MRI reliably excludes infection (100% negative predictive value) 1

• When MRI cannot be performed (e.g., implantable cardiac devices, claustrophobia):

  • Consider combination spine gallium/Tc99 bone scan 1
  • Positron emission tomography (PET) 1
  • Leukocyte scintigraphy 1
  • Single photon emission computed tomography (SPECT) 1

Microbiological Diagnosis

• For definitive diagnosis, obtain bone samples (rather than soft tissue) for culture, either intraoperatively or percutaneously 1
• Use conventional rather than molecular microbiology techniques for first-line identification of pathogens 1
• In patients with diabetic foot osteomyelitis, bone cultures are particularly indicated when:
  • Clinical and imaging evaluations yield uncertain diagnosis
  • Soft-tissue cultures are inconclusive
  • Infection has failed to respond to initial empirical antibiotic therapy
  • Considering an antibiotic regimen with high potential for selecting resistant organisms 1

Special Considerations for Different Types of Osteomyelitis

Diabetic Foot Osteomyelitis

• For diabetic foot infections, use a combination of probe-to-bone test, plain X-rays, and inflammatory markers (ESR, CRP, or PCT) as initial diagnostic studies 1
• When an ulcer or sinus tract is present, obtain wound cultures from tissues closest to the bone (avoid swab cultures due to contamination risk) 1
• MRI is the next recommended step after radiography and clinical assessment 1

Vertebral Osteomyelitis

• For suspected vertebral osteomyelitis, spine MRI is strongly recommended 1
• Consider additional tests for specific pathogens in subacute cases:
  • Brucella serologic tests in endemic areas 1
  • PPD test or interferon-γ release assay when tuberculosis is suspected 1
  • Fungal blood cultures in at-risk patients 1

Chronic Osteomyelitis

• CT is well-suited for evaluation of chronic osteomyelitis, showing periosteal reaction, trabecular coarsening, bone fragmentation, cortical erosions, and fistulae 1
• A draining sinus should prompt high clinical suspicion for chronic infection 1
• FDG-PET has shown 91% accuracy for detecting chronic osteomyelitis and may be particularly useful when hardware is present 1

Diagnostic Algorithm

1. Obtain blood cultures, inflammatory markers (CRP, ESR)
2. Perform plain radiographs
3. If radiographs are negative but clinical suspicion remains high, proceed to MRI
4. If MRI is contraindicated, use alternative nuclear medicine studies
5. When diagnosis remains uncertain after imaging, obtain bone biopsy for culture and histopathology

Remember that the gold standard for diagnosing osteomyelitis is isolation of bacteria from a reliably obtained bone sample along with histological findings of inflammatory cells and osteonecrosis 1.