What causes sudden onset sacral pain?

Causes of Sudden Onset Sacral Pain

Sudden onset sacral pain most commonly results from cauda equina syndrome, sacral insufficiency fractures, or sacral nerve compression, requiring immediate MRI evaluation to rule out emergent conditions that could lead to permanent neurological damage. 1

Urgent Causes to Consider First

Cauda Equina Syndrome (CES)

• Most serious cause requiring immediate evaluation
• Results from compression of sacral and lumbar nerve roots within the vertebral canal 1
• Clinical presentation:
  • Back pain with or without radicular symptoms
  • Bladder, bowel, or sexual dysfunction
  • Perianal or saddle numbness
  • Weakness in lower limbs
  • Sensory changes in lower limbs
  • Absent lower limb reflexes 1
• Most common cause: lumbar disc herniation at L4-L5 and L5-S1 levels
• Other etiologies: neoplasm, infection/inflammation, spinal stenosis, hemorrhage 1
• Management algorithm:
  1. If CES suspected → immediate MRI lumbar spine without IV contrast 1
  2. If MRI unavailable → CT lumbar spine without IV contrast (can detect cauda equina compression) 1
  3. Urgent neurosurgical consultation for surgical decompression 2

Sacral Insufficiency Fractures

• Common in elderly, osteoporotic patients, or those on chronic steroid therapy 3
• Presents with sudden-onset low back/sacral pain 3
• Risk factors:
  • Elderly, frail patients
  • Chronic inflammatory diseases (rheumatoid arthritis, polymyalgia rheumatica)
  • Steroid use
  • Osteoporosis 3
• Diagnosis often delayed as plain radiographs frequently miss these fractures 3
• Can present with symptoms mimicking cauda equina syndrome 4
• Diagnostic approach:
  1. MRI of sacrum (first choice)
  2. CT scan
  3. Technetium bone scintigraphy 3, 4

Sacral Nerve Compression

• Can result from trauma, fractures, or disc herniation
• May present with sudden pain and neurological symptoms
• Sacral fractures can lead to cauda equina syndrome in some cases 5
• Requires thorough clinical examination including digital rectal examination and bladder function assessment 5

Non-Urgent Causes

Musculoskeletal Pain

• Muscle strain or spasm
• Sacroiliac joint dysfunction
• Piriformis syndrome
• Often associated with activity or positional changes

Referred Pain

• Gastrointestinal conditions
• Gynecological conditions
• Urological conditions

Diagnostic Approach

Initial Assessment

• Evaluate for red flags suggesting cauda equina syndrome:
  • Bladder/bowel dysfunction
  • Saddle anesthesia
  • Bilateral leg weakness or numbness
  • Recent onset of sexual dysfunction 1

Imaging

• First-line imaging: MRI lumbar spine without IV contrast 1

  • Best for evaluating soft tissue pathology
  • Can assess vertebral marrow
  • Evaluates spinal canal patency
  • Recommended urgently for new-onset urinary symptoms with back pain 1

• Alternative if MRI contraindicated: CT lumbar spine without IV contrast

  • Can detect significant spinal stenosis
  • 50% thecal sac effacement on CT predicts significant spinal stenosis 1

• For suspected sacral insufficiency fractures:

  • MRI of sacrum
  • CT scan
  • Bone scintigraphy if MRI/CT inconclusive 3, 4

Management Considerations

1. For cauda equina syndrome:

   • Immediate neurosurgical consultation
   • Emergency surgical decompression for CESI (incomplete CES) 2
   • Next-day surgery for bilateral radiculopathy with large central disc prolapse 2

2. For sacral insufficiency fractures:

   • Pain management
   • Limited weight-bearing
   • Osteoporosis treatment
   • Monitor for complications (high morbidity and mortality) 3

3. For sacral nerve compression:

   • Multidisciplinary approach with orthopedic and neurosurgical input
   • Consider surgical decompression if neurological deficits present 5

Important Pitfalls to Avoid

• Delaying MRI in patients with suspected cauda equina syndrome
• Failing to perform thorough neurological examination including perineal sensation and rectal tone
• Missing sacral insufficiency fractures in elderly or osteoporotic patients presenting with cauda equina symptoms 4
• Focusing only on lumbar spine imaging when sacral pathology may be the cause 4

Remember that sudden onset sacral pain, especially when accompanied by neurological symptoms, requires prompt evaluation to prevent permanent neurological damage.