Spinal Infection - Pyogenic Discitis/Osteomyelitis
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
What is the diagnosis and what is the likely source?
What are the key differential diagnoses and how do you distinguish them?
What investigations would you request and why?
Describe your management plan.
What are the indications for surgical intervention?
What is the expected outcome and follow-up?
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
- Get cultures before antibiotics - yield drops dramatically after
- Disc destruction = infection - metastases spare the disc
- CRP is the best response marker - expect 50% drop by 2 weeks
- Surgery for complications - neurology, instability, failed therapy
- 6 weeks IV minimum - shorter courses have higher failure rates
- Look for the source - UTI, skin, dental, IVDU, endocarditis
- 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