Tumor biology and incidence
- Most common in children, with two age peaks: children less than age 2 and children between ages 8 and 10
- Blood flow through metaphyseal bone slows in growing bones of children, allowing for more turbulent flow and decreased phagocytosis; predispose to infection
- Staphylococcus aureus most common infecting organism
Presentation and physical findings
- In early stages, may not present with systemic signs
- In chronic form, patients may present with history of pain of several months' duration.
- Blood work
- Normal to elevated white blood cell count
- Elevated erythrocyte sedimentation rate (ESR); usually takes 3-5 days to reach its peak
- Elevated C-reactive protein; reaches peak by day 2 postinfection; more accurate than ESR for monitoring progress of treatment.
Radiographic appearance
Within 24 hours of infection
- Evidence of osteomyelitis
- Soft tissue swelling, loss of definition between fascial planes
Within 7-10 days of infection
- Destructive lytic lesion may be present
- Lesion positive on bone scan
Within 2-6 weeks of infection
- Progressive bony destruction of cortical and medullary bone
- Endosteal sclerosis and periosteal reaction are usually present.
Within 6-8 weeks of infection
- Sequestra, indicating areas of necrotic bone
- May be surrounded by a dense involucrum (periosteal new bone formation)
Nuclear medicine
Children
- Technetium 99m diphosphinate bone scan indicated in most cases
- False negatives increased if performed in first 24 hours after infection
- False positves seen with trauma and tumor
Adults
- Sequential technetium-gallium excellent at finding vertebral osteomyelitis
- Indium-labelled leukocyte scan more accurate for detecting subclinical osteomyelitis
MRI
Superior to indium-labelled leukocyte scan in defining extent of infection
Differential diagnosis
- In acute stage, eosinophilic granuloma and Ewing sarcoma
- Can simulate many conditions
Pathology
- Reactive inflammatory cell infiltrate (lymphocytes and plasma cells)
- Neutrophils generally not present
- Mixed cellular infiltrate usually indicates a benign diagnosis
- Necrotic bone and marrow fibrosis also present
Diagnosis and treatment
- Individualize to specific case
- All patients will require antibiotics, with or without surgical debridement
Associated condition: Brodie's abscess
- Form of chronic osteomyelitis usually seen in lower extremities of young adults
- Often insidious bone infection; usually localized to metaphysis of tibia or femur
- Usually has elongated shape and well-demarcated margin; surrounded by reactive sclerotic bone
- May see radiolucent tract extending away from lesion into growth plate
- Sequestra usually absent
