Can focal epidural lipomatosis be confused with osteomyelitis?

Differentiating Focal Epidural Lipomatosis from Osteomyelitis

Focal epidural lipomatosis can be confused with osteomyelitis on imaging, leading to potential misdiagnosis and inappropriate treatment. This distinction is critical as the management approaches differ significantly, with osteomyelitis requiring antimicrobial therapy while epidural lipomatosis may require surgical decompression or conservative management.

Imaging Characteristics and Diagnostic Challenges

MRI Findings

• Epidural Lipomatosis:

  • Appears as abnormal accumulation of unencapsulated adipose tissue in the epidural space
  • High signal intensity on T1-weighted images
  • Fat suppression sequences show signal dropout
  • May cause compression of neural structures similar to infection
  • Often more diffuse but can present focally 1

• Osteomyelitis:

  • Low signal intensity on T1-weighted images
  • High signal intensity on T2-weighted images
  • Enhancement with gadolinium
  • May show associated abscess formation or soft tissue inflammation
  • Often involves vertebral endplates and disc spaces 2

Diagnostic Pitfalls

1. Focal epidural lipomatosis can mimic disc herniation or abscess formation, particularly when it progresses rapidly 3
2. Both conditions can cause similar neurological symptoms including radiculopathy and myelopathy
3. Post-procedural changes (after spine surgery) can further complicate differentiation 3

Key Differentiating Factors

Clinical Presentation

• Epidural Lipomatosis:

  • Often associated with exogenous steroid use and obesity
  • May be asymptomatic or cause neurogenic claudication
  • Typically lacks systemic inflammatory signs (fever, elevated WBC)
  • Can be considered a spinal hallmark of metabolic syndrome 1

• Osteomyelitis:

  • Often presents with fever, back pain, and elevated inflammatory markers
  • May have risk factors such as diabetes, IV drug use, or recent infection
  • Frequently associated with elevated ESR and CRP 2

Diagnostic Approach

1. Laboratory Testing:

   • Obtain ESR, CRP, and WBC count with differential
   • Blood cultures if osteomyelitis is suspected 2

2. Advanced Imaging:

   • MRI with gadolinium is the imaging modality of choice for both conditions
   • FDG-PET/CT may help differentiate in challenging cases (higher uptake in infection) 2
   • Fat suppression sequences are crucial to identify epidural lipomatosis 1

3. Tissue Sampling:

   • Image-guided aspiration or biopsy is definitive for diagnosing osteomyelitis
   • Histopathological examination can distinguish fat from infectious material 2

Management Considerations

For Confirmed Epidural Lipomatosis:

• Risk factor control (weight loss, steroid discontinuation if possible)
• Surgical decompression if conservative treatment fails or with severe neurological symptoms 1
• Microsurgical decompression has shown good outcomes comparable to those for classical spinal stenosis 4

For Confirmed Osteomyelitis:

• Antimicrobial therapy for at least 6 weeks (8 weeks for MRSA)
• Surgical debridement may be necessary, especially with necrotic bone
• Close monitoring of inflammatory markers to assess treatment response 5

Prevalence and Risk Assessment

The prevalence of spinal epidural lipomatosis is approximately 2.5% among patients undergoing spine MRI, with only 0.1% being symptomatic specifically due to the lipomatosis 6. Risk factors associated with epidural lipomatosis include:

• Older age
• Male sex
• BMI > 30
• Black/African American race
• Systemic corticosteroid use
• Epidural corticosteroid injections 6

Conclusion

When faced with imaging findings that could represent either focal epidural lipomatosis or osteomyelitis, clinicians should consider:

1. Clinical context (presence of inflammatory signs, risk factors)
2. Specific MRI characteristics (signal intensity, fat suppression behavior)
3. Laboratory findings (inflammatory markers)
4. Need for tissue sampling in uncertain cases

Misdiagnosis can lead to unnecessary antibiotic treatment or delayed appropriate intervention, significantly impacting patient morbidity and quality of life.