# CIM Case: Spinal Infection - Pyogenic Discitis/Osteomyelitis ## Clinical Scenario **Patient:** 56-year-old hospital worker (nurse) **Presentation:** 4-week history of severe unremitting low back pain, low-grade fevers, unable to work **Relevant history:** Type 2 diabetes (poorly controlled, HbA1c 9.5%), recent urinary tract infection treated with oral antibiotics 6 weeks ago, no IVDU, no recent spinal procedures, no prior back surgery, no immunosuppression **Examination findings:** - Febrile (38.2°C) - Appears unwell, diaphoretic - Severe tenderness over L3-L4 spinous processes - Paraspinal muscle spasm - Restricted range of motion in all planes due to pain - No neurological deficit (power, sensation, reflexes normal) - No saddle anaesthesia - Anal tone normal - Abdominal examination: suprapubic tenderness --- ## Investigations Provided ### Laboratory Results | Test | Result | Normal Range | Interpretation | |------|--------|--------------|----------------| | Hb | 103 g/L | 115-155 g/L | ↓ Anaemia of chronic disease | | WCC | 14.5 ×10⁹/L | 4-11 ×10⁹/L | ↑ Leucocytosis | | Platelets | 385 ×10⁹/L | 150-400 ×10⁹/L | Normal | | CRP | 185 mg/L | <5 mg/L | ↑ Markedly elevated | | ESR | 98 mm/hr | <20 mm/hr | ↑ Markedly elevated | | Procalcitonin | 2.5 ng/mL | <0.5 ng/mL | ↑ Elevated (bacterial infection) | | Albumin | 28 g/L | 35-50 g/L | ↓ Low | | ALP | 145 U/L | 30-120 U/L | ↑ Mildly elevated | | GGT | 85 U/L | <60 U/L | ↑ Elevated | | HbA1c | 9.5% | <6.5% | ↑ Poor glycaemic control | | Creatinine | 95 μmol/L | 45-90 μmol/L | ↑ Mildly elevated | | Urine MCS | E. coli >100,000/mL | - | Active UTI | | Blood cultures | Pending | - | Await results | ### Imaging **Image 1: Lumbar Spine X-ray (AP and Lateral)** **Radiological features:** - Loss of disc space height at L3-L4 - Irregular endplates L3 inferior and L4 superior - Early erosive changes - No significant kyphosis - No vertebral collapse **Image 2: MRI Lumbar Spine (T1, T2, STIR, Post-contrast)** **Findings:** - **L3-L4 disc space**: T2 hyperintense (fluid), loss of normal intranuclear cleft - **Vertebral bodies**: T1 hypointense, T2/STIR hyperintense marrow oedema in L3 and L4 - **Endplates**: Erosions and irregularity at L3-L4 - **Enhancement**: Disc and adjacent vertebral bodies enhance post-gadolinium - **Epidural space**: Small epidural phlegmon (no discrete abscess) - **No cord compression** (conus terminates at L1) - **Psoas**: Mild bilateral psoas oedema, no abscess --- ## Questions & Model Answers **Diagnosis: Pyogenic Spondylodiscitis (Vertebral Osteomyelitis with Discitis) L3-L4** **Likely Source: Haematogenous spread from urinary tract infection (E. coli)** **Evidence for Diagnosis:** | Feature | Significance | |---------|--------------| | Severe back pain with fever | Classic presentation | | Elevated inflammatory markers | CRP 185, ESR 98 | | MRI findings | Disc destruction, endplate erosion, marrow oedema | | Risk factors | Diabetes, recent UTI | | Positive urine culture | E. coli - common cause | **Routes of Infection:** | Route | Mechanism | This Patient | |-------|-----------|--------------| | **Haematogenous** | Bacteraemia seeds vertebral body | ✓ Most likely (UTI source) | | Direct inoculation | Post-procedure (discography, surgery) | No recent procedures | | Contiguous spread | From adjacent infected tissue | No adjacent focus | **Why L3-L4?** - Lumbar spine most common location (58%) - Rich arterial supply to vertebral bodies - Venous drainage via Batson's plexus (connects pelvic veins to spine) - UTI organisms can spread via pelvic venous plexus > **Consultant Tip:** Always look for the source! UTI, skin/soft tissue, dental, IVDU, endocarditis. E. coli from UTI is the second most common organism after S. aureus. **Differential Diagnosis:** | Diagnosis | Supporting Features | Against | |-----------|---------------------|---------| | **Pyogenic spondylodiscitis** | Fever, elevated WCC/CRP, disc destruction | - | | Tuberculous spondylitis (Pott's) | Disc destruction, back pain | Acute presentation, not from endemic area | | Metastatic disease | Severe back pain, age | Disc involvement (mets spare disc), fever | | Myeloma | Back pain, age | Disc involved, fever, no paraprotein | | Degenerative disc disease | Back pain | Fever, elevated markers, MRI pattern | **Key Distinguishing Features:** | Feature | Pyogenic | Tuberculous | Tumour | |---------|----------|-------------|--------| | Onset | Days-weeks | Months | Variable | | Fever | Common | May be absent | Rare | | Disc space | **Destroyed early** | **Destroyed** | **Preserved** | | Endplates | Eroded | Eroded | May be preserved | | Abscess | Common | Very common (cold abscess) | Rare | | Skip lesions | Rare | Common (30%) | Common | | Calcification | Rare | May occur | Rare | **MRI Patterns:** | Finding | Infection | Tumour | |---------|-----------|--------| | Disc T2 signal | Increased (fluid) | Normal (preserved) | | Enhancement pattern | Disc + vertebrae | Vertebrae only | | Posterior elements | Usually spared | Often involved in mets | | Soft tissue | Phlegmon/abscess | Mass without rim enhancement | > **Consultant Tip:** Metastatic tumours DO NOT destroy the disc - this is the key differentiator. If the disc is destroyed, think infection (pyogenic or TB). **Essential Investigations:** | Investigation | Purpose | Expected Finding | |---------------|---------|------------------| | **Blood cultures (×3)** | Identify organism | Positive in 30-60% | | **MRI spine (whole)** | Confirm diagnosis, extent, abscess | L3-L4 discitis ± epidural disease | | **CT-guided biopsy** | Tissue diagnosis, culture | Organism identification | | **Echocardiogram** | Rule out endocarditis | Vegetations if present | | **Urine culture** | Source identification | E. coli (done - positive) | **Extended Workup:** | Test | Indication | |------|------------| | HIV test | Risk factor for atypical organisms | | HbA1c | Assess diabetes control | | TTE/TOE | If S. aureus bacteraemia or clinical concern | | CT CAP | If malignancy cannot be excluded | | Procalcitonin | Bacterial vs non-bacterial | **CT-Guided Biopsy:** | Consideration | Details | |---------------|---------| | Timing | Before antibiotics if stable | | Yield | 50-70% culture positive | | Samples | Aerobic, anaerobic, TB, fungal, histology | | Technique | Transpedicular or posterolateral approach | **When NOT to Biopsy:** - Positive blood cultures with consistent clinical picture - Neurological emergency (operate first) - Obvious source with same organism (e.g., E. coli in urine and blood) **For This Patient:** - Blood cultures already sent - Urine positive for E. coli - If blood cultures also grow E. coli → biopsy may not be needed - If blood cultures negative → CT-guided biopsy indicated > **Consultant Tip:** Get cultures BEFORE starting antibiotics. Once antibiotics are started, culture yield drops significantly. If blood cultures positive with same organism as urine, you may not need a biopsy. **Initial Management:** | Step | Action | |------|--------| | 1. Admission | Ward or HDU depending on sepsis severity | | 2. Blood cultures | If not already done | | 3. IV access | Large bore, anticipate long-term IV therapy | | 4. Analgesia | Multimodal, may need PCA | | 5. Glycaemic control | Optimise diabetes | | 6. Bed rest | Initially, to reduce mechanical stress | **Antibiotic Therapy:** | Phase | Duration | Route | Regimen | |-------|----------|-------|---------| | **Empirical** | Until cultures | IV | Flucloxacillin + ciprofloxacin (covers S. aureus + E. coli) | | **Targeted** | 6 weeks total | IV | Based on culture sensitivities | | **Consolidation** | Variable | Oral | 6-12 weeks total depending on response | **This Patient (E. coli likely):** - **Ciprofloxacin** 400mg IV BD + **Flucloxacillin** 2g IV Q6H (empirical) - Narrow when sensitivities available - Total course: 6 weeks IV, consider oral switch **Indications for Surgery:** | Absolute | Relative | |----------|----------| | Neurological deficit | Large epidural abscess | | Progressive deformity | Failed medical therapy (no response in 4-6 weeks) | | Spinal instability | Significant bone destruction | | Large abscess not draining | Persistent bacteraemia | **This Patient:** No neurological deficit, small phlegmon → **Medical management appropriate** **Monitoring:** | Parameter | Frequency | Target | |-----------|-----------|--------| | Temperature | Daily | Afebrile by day 3-5 | | CRP | Twice weekly | 50% reduction by 2 weeks | | Neurology | Daily | No deterioration | | Pain | Daily | Improving | | MRI | 6 weeks | Improvement or stability | > **Consultant Tip:** CRP is the best marker for treatment response. Expect 50% reduction in 2 weeks. If CRP not falling, reassess - wrong organism, abscess not draining, or resistant bug. **Surgical Indications:** | Indication | Urgency | Procedure | |------------|---------|-----------| | **Neurological deficit** | Emergency | Decompression ± stabilisation | | **Epidural abscess with deficit** | Emergency | Laminectomy, abscess drainage | | **Progressive kyphosis** | Semi-urgent | Debridement + reconstruction | | **Spinal instability** | Semi-urgent | Stabilisation | | **Failed medical therapy** | Elective | Debridement ± stabilisation | | **Large undrained abscess** | Semi-urgent | Drainage ± stabilisation | **Surgical Approaches:** | Approach | Indication | |----------|------------| | **Posterior** | Epidural abscess, posterior instrumentation | | **Anterior** | Vertebral body debridement, anterior reconstruction | | **Combined** | Extensive destruction, circumferential disease | | **Minimally invasive** | Abscess drainage, biopsy | **Posterior Decompression and Stabilisation:** - Laminectomy for cord/cauda decompression - Pedicle screw fixation 2 levels above and below - Debride infected tissue - Consider staged anterior reconstruction **Anterior Debridement and Reconstruction:** - Corpectomy of involved vertebrae - Debridement of disc and endplates - Reconstruction with cage (PEEK or titanium mesh) - Anterior or posterior stabilisation **This Patient:** - No neurological deficit - Small epidural phlegmon (not abscess) - No significant instability **→ Continue medical management with close monitoring** > **Consultant Tip:** Most spinal infections can be treated non-operatively. Surgery is for complications - neurology, instability, failed medical therapy, or significant abscess. **Expected Outcomes:** | Outcome | Percentage | |---------|------------| | Complete resolution with medical therapy | 70-80% | | Requiring surgery | 20-30% | | Neurological recovery (if surgery for deficit) | 60-70% | | Chronic back pain | 30-50% | | Recurrence | 5-10% | | Mortality | 2-5% | **Prognostic Factors:** | Factor | Impact | |--------|--------| | Delay in diagnosis | Worse outcomes | | Neurological deficit at presentation | May not recover fully | | Diabetes/immunocompromise | Slower response, higher complications | | S. aureus vs E. coli | S. aureus may be more aggressive | | Abscess requiring drainage | May need longer treatment | **Follow-up Protocol:** | Time | Assessment | |------|------------| | Weekly (inpatient) | Clinical review, CRP | | 2 weeks | Reassess therapy, consider PICC for home IV | | 6 weeks | End IV therapy, repeat MRI | | 3 months | Clinical review, inflammatory markers | | 6 months | Final MRI to confirm healing | | 12 months | Clinical review if symptoms | **MRI Interpretation During Treatment:** | Finding | Interpretation | |---------|----------------| | Persistent enhancement | Common, may persist for months | | Stable or improving marrow oedema | Good response | | New epidural collection | May need intervention | | Progressive bone destruction | Treatment failure | **Return to Work:** - Sedentary work: 6-8 weeks - Light physical: 3 months - Heavy physical: 6+ months (may need restrictions) **Long-term Complications:** - Chronic back pain (most common) - Residual kyphosis - Adjacent segment degeneration (if fused) - Recurrent infection (rare) > **Consultant Tip:** MRI changes lag behind clinical improvement. Don't be alarmed by persistent enhancement at 6 weeks if the patient is clinically better with falling CRP. Repeat MRI at 3-6 months to confirm healing. --- ## Key Teaching Points ### Pattern Recognition **This pattern suggests Pyogenic Spondylodiscitis:** - Severe back pain out of proportion - Fever and malaise - Elevated CRP and ESR - Risk factors (diabetes, IVDU, UTI, recent procedure) - MRI: disc destruction, endplate erosion, marrow oedema **Differentiate from TB:** | Feature | Pyogenic | Tuberculous | |---------|----------|-------------| | Onset | Acute (weeks) | Insidious (months) | | Fever | High-grade | Low-grade or absent | | CRP | Very elevated | Mildly elevated | | Skip lesions | Rare | Common (30%) | | Kyphosis | Mild | Severe ("gibbus") | | Response to treatment | Weeks | Months | ### Critical Management Points 1. **Get cultures before antibiotics** - yield drops dramatically after 2. **Disc destruction = infection** - metastases spare the disc 3. **CRP is the best response marker** - expect 50% drop by 2 weeks 4. **Surgery for complications** - neurology, instability, failed therapy 5. **6 weeks IV minimum** - shorter courses have higher failure rates 6. **Look for the source** - UTI, skin, dental, IVDU, endocarditis 7. **Echo for S. aureus** - high rate of concurrent endocarditis --- ## Common Examiner Follow-ups **Q: "When would you consider echocardiography?"** Echocardiography indications in spinal infection: | Indication | Reason | |------------|--------| | S. aureus bacteraemia | 10-15% have concurrent endocarditis | | Multiple embolic sites | Suggests cardiac source | | New murmur | Valvular vegetations | | IVDU | High risk of right-sided endocarditis | | Prosthetic valve | Very high risk | | Persistent bacteraemia | Consider uncontrolled source | For this patient: If blood cultures grow S. aureus → mandatory echo (TTE, consider TOE). --- **Q: "What is the role of bracing?"** Bracing in spinal infection: | Indication | Type | Duration | |------------|------|----------| | Lumbar discitis | TLSO | 6-12 weeks | | Thoracic | TLSO | 6-12 weeks | | Cervical | Hard collar | 6-12 weeks | Benefits: - Pain relief - Reduces mechanical stress - May limit deformity progression Not a substitute for antibiotics or surgery when indicated. --- **Q: "What organisms would you consider in IVDU?"** Organisms in IV drug users: | Organism | Frequency | Notes | |----------|-----------|-------| | S. aureus (MRSA) | Most common | Often MRSA | | Pseudomonas | 10-15% | Cervical spine predilection | | Candida | 5-10% | Consider in failed treatment | | Polymicrobial | 10-20% | Multiple organisms | Empirical therapy in IVDU: Vancomycin + anti-pseudomonal beta-lactam (e.g., ceftazidime) --- **Q: "How do you differentiate Modic type 1 changes from infection?"** Modic type 1 vs Infection: | Feature | Modic 1 | Infection | |---------|---------|-----------| | Disc height | Preserved | Lost | | Endplates | Intact | Eroded | | Enhancement | Linear | Diffuse | | Disc signal | Normal | Abnormal (high T2) | | Clinical | Chronic pain | Fever, acute pain | | Inflammatory markers | Normal | Elevated | When in doubt, CT-guided biopsy is definitive. --- ## Related Topics - Spinal Tuberculosis - Epidural Abscess - Antibiotic Therapy in Bone Infection - Spinal Instrumentation in Infection - Septic Arthritis - Osteomyelitis