# CIM Case: Paediatric Acute Osteomyelitis ## Clinical Scenario **Patient:** 7-year-old boy **Presentation:** 5-day history of right leg pain, fever (38.8°C), and refusal to weight-bear **Relevant history:** Previously well child, no recent trauma, no immunocompromise. Attends school swimming. **Examination findings:** - Tender, swollen distal tibia with overlying erythema and warmth - Unable to actively dorsiflex ankle due to pain - Knee and hip movements painless (important to exclude septic arthritis) - No draining sinus --- ## Investigations Provided ### Laboratory Results | Test | Result | Normal Range | Interpretation | |------|--------|--------------|----------------| | Hb | 118 g/L | 115-135 g/L | Normal | | WCC | 18.5 ×10⁹/L | 5-13 ×10⁹/L | ↑ Leucocytosis | | Neutrophils | 14.2 ×10⁹/L | 1.5-8.0 ×10⁹/L | ↑ Left shift | | Platelets | 420 ×10⁹/L | 150-400 ×10⁹/L | ↑ Reactive thrombocytosis | | CRP | 186 mg/L | <5 mg/L | ↑↑ Significantly elevated | | ESR | 68 mm/hr | <10 mm/hr | ↑↑ Elevated | | Blood cultures | Pending | Negative | Awaiting result | | Procalcitonin | 2.4 ng/mL | <0.5 ng/mL | ↑ Suggests bacterial infection | ### Imaging **Image 1: AP and Lateral Radiograph of Right Tibia** **Radiological features:** - Soft tissue swelling overlying distal tibial metaphysis - Loss of normal fat planes - Subtle periosteal thickening along distal tibial shaft - No obvious lytic lesion (early presentation - bone changes take 10-14 days) - Growth plates appear normal **Image 2: MRI Right Tibia (T1, T2/STIR, Post-contrast)** **MRI findings:** - Extensive bone marrow oedema in distal tibial metaphysis (low T1, high STIR signal) - 12mm subperiosteal abscess collection along anterolateral tibia - Periosteal elevation with rim enhancement - Inflammatory changes in adjacent soft tissues - Intact physis with no transphyseal spread - No associated joint effusion (excludes concurrent septic arthritis) --- ## Questions & Model Answers **Blood Tests:** The laboratory results show evidence of acute bacterial infection: - Leucocytosis (WCC 18.5) with neutrophilia indicating active bacterial infection - Markedly elevated CRP (186 mg/L) - most useful marker for monitoring response - Elevated ESR (68 mm/hr) - useful baseline for long-term monitoring - Reactive thrombocytosis - common in acute infection - Elevated procalcitonin supports bacterial rather than viral aetiology **Imaging:** The plain radiograph shows: - Early changes with soft tissue swelling and subtle periosteal reaction - No established bone destruction (expected in early disease) The MRI demonstrates: - Classic features of acute osteomyelitis - metaphyseal bone marrow oedema - Subperiosteal abscess formation requiring surgical drainage - No physeal involvement or joint effusion - good prognostic features > **Key Point:** MRI is gold standard but don't delay antibiotics for imaging. Blood cultures BEFORE antibiotics. | Diagnosis | Supporting Features | Against | |-----------|---------------------|---------| | **Acute haematogenous osteomyelitis** | Fever, metaphyseal location, elevated inflammatory markers, MRI findings | - | | Septic arthritis | Fever, inability to weight bear | No joint effusion on MRI, ankle movements possible | | Ewing sarcoma | Child, diaphyseal/metaphyseal lesion | Acute presentation, elevated inflammatory markers, no permeative destruction | | Stress fracture | Pain, swelling | Fever, very high CRP, no typical fracture line | | Chronic recurrent multifocal osteomyelitis (CRMO) | Child, bone involvement | Acute presentation, high CRP, single focus | **My leading diagnosis is acute haematogenous osteomyelitis** because: - Classic presentation: fever, localised pain, inability to weight bear - Typical age and location (metaphysis of long bone) - Markedly elevated inflammatory markers - MRI features of marrow oedema with subperiosteal abscess > **Consultant Tip:** In paediatric bone infection, always exclude septic arthritis - check the adjacent joint. **For Diagnosis:** - Blood cultures x 2 from separate sites (positive in 30-50%) - Aspirate subperiosteal collection for MC&S (higher yield than blood cultures) - Consider bone biopsy if diagnosis unclear or atypical features **Organism Identification:** - Most common organism: *Staphylococcus aureus* (80-90%) - Consider: *Kingella kingae* (under 5 years), *Streptococcus*, *Haemophilus* (unvaccinated) - Extended cultures if immunocompromised **Initial Antibiotic Management:** - **First line:** IV Flucloxacillin 50mg/kg (max 2g) QID - Covers MSSA which causes majority of paediatric osteomyelitis - **If MRSA risk factors:** Add IV Vancomycin 15mg/kg QID (monitor trough levels) - MRSA risk: previous colonisation, healthcare exposure, community MRSA endemic area **Monitoring:** - Daily clinical assessment and temperature chart - CRP every 48-72 hours (most useful monitoring marker) - Baseline UEC/LFTs for antibiotic toxicity monitoring > **Consultant Tip:** Flucloxacillin is first-line for MSSA. Don't forget blood cultures BEFORE antibiotics! **Indication for Surgery:** This patient requires surgical intervention due to: - Subperiosteal abscess >3mm on MRI - Abscess formation = surgical drainage required **Surgical Principles:** 1. **Incision and drainage** of subperiosteal collection 2. **Cortical fenestration** (drill holes) to decompress intramedullary pressure 3. **Multiple tissue samples** (minimum 3) for MC&S before antibiotics if possible 4. **Thorough debridement** of necrotic tissue 5. **Lavage** with saline 6. **Wound closure** - primary closure if clean, leave open if contaminated **Post-operative Care:** - Continue IV antibiotics minimum 3-5 days until clinical improvement - Switch to oral when: afebrile >48 hours, improving clinically, CRP falling - Total antibiotic duration: 3-4 weeks minimum (some advocate 6 weeks) - Consider PICC line if prolonged IV therapy anticipated > **Consultant Tip:** Abscess = surgery. Don't delay drainage waiting for 'failed antibiotics' if abscess clearly present on MRI. **Diagnosis:** Red Man Syndrome (Vancomycin Infusion Reaction) **Pathophysiology:** - NOT a true allergy - histamine-mediated reaction - Due to rapid infusion causing mast cell degranulation - Rate-dependent phenomenon (too fast infusion) **Clinical Features:** - Erythematous rash affecting face, neck, upper torso - Flushing and pruritus - Hypotension if severe - Occurs during or shortly after infusion **Immediate Management:** 1. Slow or temporarily cease infusion 2. Administer antihistamine (e.g., promethazine) 3. Monitor vital signs **Prevention of Recurrence:** - Extend infusion time to minimum 1-2 hours (ideally 500mg over 1 hour minimum) - Pre-medicate with antihistamine for subsequent doses - **NOT a contraindication to future vancomycin use** **Differentiating from True Allergy:** - True allergy: anaphylaxis, urticaria, severe rash persisting after stopping drug - Red man syndrome: rate-related, resolves with slower infusion > **Consultant Tip:** Red Man Syndrome is rate-related, not a true allergy. Slow the infusion. Can continue vancomycin safely. **Concerns:** 1. Inadequate source control (undrained collection) 2. Resistant organism (check sensitivities) 3. Development of new collection or spread 4. Wrong diagnosis (rare but consider) **Assessment:** - Thorough re-examination of the limb - Review culture sensitivities urgently - Repeat MRI to assess for undrained collection **Actions:** | Action | Rationale | |--------|-----------| | Repeat MRI | Assess for inadequate drainage or new collection | | Surgical re-exploration | Most likely cause is persistent/recurrent abscess | | Antibiotic review | Confirm sensitivities, ensure adequate dosing | | ID consultation | Complex infection requiring specialist input | | Check vancomycin trough | Target 15-20 mg/L for severe infection | **Vancomycin Monitoring:** - Trough level before 4th dose - Target: 15-20 mg/L for serious MRSA infection - Monitor renal function (nephrotoxicity) - Consider adding rifampicin (specialist advice) for biofilm penetration > **Consultant Tip:** Rising CRP despite treatment = inadequate source control or resistant organism. Act promptly - repeat imaging and consider re-operation. --- ## Key Teaching Points ### Pattern Recognition **This pattern suggests Acute Haematogenous Osteomyelitis:** - Child with fever, localised bone pain, and refusal to weight bear - Metaphyseal location (vascular anatomy predisposes this area) - Elevated inflammatory markers (CRP >100, leucocytosis) - MRI: marrow oedema with periosteal reaction ± abscess **Distinguish from Septic Arthritis:** - Septic arthritis: joint effusion, severely restricted ROM in all planes - Osteomyelitis: metaphyseal tenderness, may have preserved joint movement - Can coexist (especially hip) - always image the adjacent joint **Distinguish from Ewing Sarcoma:** - Ewing: more chronic presentation, "onion-skin" periosteal reaction, permeative destruction - Osteomyelitis: acute illness, soft tissue abscess, responds to antibiotics ### Critical Management Points 1. **Blood cultures before antibiotics** - positive in 30-50% 2. **MRI is gold standard** - but don't delay antibiotics 3. **Abscess = surgery** - drainage is essential 4. **CRP for monitoring** - most useful marker for response 5. **Duration: 3-6 weeks total** - IV to oral switch when improving --- ## Common Examiner Follow-ups **Q: "What organism is most likely in a 2-year-old with osteomyelitis?"** *Kingella kingae* is increasingly recognised in children aged 6 months to 4 years. Standard cultures may miss it - requires prolonged incubation and specific culture techniques. Consider if blood cultures negative but clinical picture fits. --- **Q: "What are the complications of paediatric osteomyelitis?"** | Complication | Features | |--------------|----------| | Chronic osteomyelitis | Sequestrum, involucrum, sinus formation | | Growth disturbance | If physis involved - angular deformity, limb length discrepancy | | Pathological fracture | Through weakened bone | | Septic arthritis | Spread to adjacent joint (especially hip) | | Sepsis/metastatic infection | Endocarditis, septic emboli | --- **Q: "When would you consider this child has chronic osteomyelitis?"** Chronic osteomyelitis is defined as symptoms persisting beyond 6 weeks or recurrence after treatment. Radiographic features include: - Sequestrum (dead bone) - Involucrum (new bone formation around sequestrum) - Cloaca (drainage tract through involucrum) - Sinus tract formation --- **Q: "What are the Kocher criteria and when do you use them?"** Kocher criteria are used to distinguish septic arthritis from transient synovitis of the hip in children: 1. Fever >38.5°C 2. Non-weight bearing 3. WCC >12,000 4. ESR >40 mm/hr Probability of septic arthritis: 0 criteria = 0.2%, 4 criteria = 99.6% --- ## Related Topics - Septic Arthritis (Paediatric) - Chronic Osteomyelitis - MRSA Infections in Orthopaedics - Transient Synovitis vs Septic Hip - Kocher Criteria