What are the initial workup tests for a lump on the lower back with a recent history of fever in a child?

Initial Workup Tests for a Lump on the Lower Back with Recent Fever in a Child

The initial workup for a child with a lump on the lower back and recent fever should include MRI of the spine with and without contrast as the primary imaging study, along with laboratory tests including complete blood count (CBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) to evaluate for spinal infection such as discitis or epidural abscess.

Initial Clinical Evaluation

• Focus on the characteristics of the lump, duration of fever, and any associated neurological symptoms such as limping, motor weakness, or bladder/bowel dysfunction 1
• Assess for risk factors including recent infections (particularly urinary tract infections), immunocompromised status, or recent spine procedures 1
• Evaluate for signs of neurologic compromise which may indicate epidural abscess or spinal cord compression requiring urgent intervention 1

Laboratory Testing

• Complete blood count (CBC) with differential to assess for leukocytosis, which may indicate bacterial infection 1, 2
• Erythrocyte sedimentation rate (ESR) - values >40 mm/h have high sensitivity for inflammatory conditions, while values >100 mm/h have high specificity for serious infections 3
• C-reactive protein (CRP) - rises and falls more rapidly than ESR with changes in inflammation 1, 3
• Blood cultures to identify potential causative organisms if systemic infection is suspected 1, 4
• Urinalysis and urine culture to rule out urinary tract infection as a source of fever, especially in children with recurrent UTIs 1, 5

Imaging Studies

• MRI of the spine with and without IV contrast is the imaging modality of choice for suspected spinal infection 1

  • MRI can identify discitis, osteomyelitis, epidural abscess, and paraspinal soft tissue involvement 1
  • The entire spine should be imaged if multifocal infection is suspected 1

• Plain radiographs of the spine area of interest may be complementary but have low sensitivity for early infection 1

  • Radiographs may help guide surgical management if decompression and stabilization are needed 1

Special Considerations

• In children, spine infection often initially affects the intervertebral disc rather than the vertebral endplate (which is more common in adults) 1
• Epidural abscess has increased in incidence and can lead to significant neurologic morbidity if diagnosis is delayed 1
• A high index of clinical suspicion is required to initiate appropriate workup for spine infection 1
• If initial imaging is normal but symptoms persist, follow-up imaging should be considered as some infections may only become visible on follow-up studies 1

Pitfalls to Avoid

• Relying solely on plain radiographs, which have low sensitivity for early spine infection 1
• Failing to consider spinal infection in a child with fever and back symptoms, even without neurological deficits 1
• Delaying MRI when there is clinical suspicion of epidural abscess, as this can lead to increased morbidity 1
• Overlooking the possibility of discitis/osteomyelitis in a child with recurrent urinary tract infections 5

Algorithm for Workup

1. Obtain laboratory studies (CBC, ESR, CRP, blood cultures) 1, 3
2. If neurological deficits are present, proceed directly to MRI spine with and without contrast 1
3. For stable patients without neurological deficits, consider plain radiographs of the spine area of interest 1
4. Regardless of radiograph findings, proceed to MRI spine with and without contrast if clinical suspicion for infection remains 1
5. Consider additional testing based on clinical presentation:
   • Lumbar puncture if meningitis is suspected 6
   • Urinalysis and urine culture if UTI is suspected 1