What is the next best step for a patient presenting with severe back pain and urinary incontinence?

Immediate Evaluation for Cauda Equina Syndrome

This patient requires urgent MRI of the lumbar spine and immediate neurosurgical consultation to rule out cauda equina syndrome, as the combination of severe back pain and urinary incontinence represents a neurosurgical emergency until proven otherwise. 1

Critical Red Flags Present

This presentation contains two cardinal features of cauda equina syndrome:

• Severe back pain combined with urinary incontinence 1
• Urinary retention has 90% sensitivity for cauda equina syndrome, but incontinence (particularly overflow incontinence from retention) is also a key presenting feature 1, 2
• The most frequent finding in cauda equina syndrome is urinary retention (90% sensitivity), though fecal incontinence and bladder dysfunction of any type warrant immediate evaluation 1

Immediate Diagnostic Steps

Physical Examination Must Include:

• Neurologic examination assessing for motor deficits at multiple levels, particularly testing knee strength/reflexes (L4), great toe/foot dorsiflexion (L5), and foot plantarflexion/ankle reflexes (S1) 1
• Straight-leg-raise testing to assess for nerve root compression 1
• Perineal sensation to evaluate for saddle anesthesia 1
• Rectal examination to assess sphincter tone and rule out fecal incontinence 1
• Post-void residual measurement to determine if urinary retention is present 1

Urgent Imaging:

• MRI of the lumbar spine is the definitive imaging modality and must be obtained emergently if cauda equina syndrome is suspected 2
• Do not delay imaging for urinalysis or other ancillary testing if red flag symptoms are present 1

Differential Considerations While Awaiting Imaging

Other Serious Spinal Pathology:

• Vertebral osteomyelitis: Obtain two sets of blood cultures and baseline ESR/CRP, perform careful spinal percussion 2
• Note that fever is present in only 45% of bacterial vertebral osteomyelitis cases, so absence does not exclude diagnosis 2
• Epidural abscess: Can present similarly and requires urgent MRI 2
• Massive disc herniation: More than 90% of symptomatic herniations occur at L4/L5 or L5/S1 levels 1

Lumbar Spinal Stenosis:

• Can cause overactive bladder symptoms that worsen with walking due to circulatory disturbance of the cauda equina 3
• However, acute presentation with severe pain and incontinence suggests more urgent pathology 3

Critical Management Pitfalls

• Do not attribute incontinence to benign causes (overactive bladder, stress incontinence) without first excluding cauda equina syndrome in the setting of severe back pain 1
• Do not delay evaluation for urodynamic studies or conservative management trials when red flags are present 1, 2
• Do not miss early vertebral osteomyelitis: Maintain high suspicion even without fever, as average time to diagnosis is 2-4 months 2
• In patients without urinary retention, the probability of cauda equina syndrome is approximately 1 in 10,000, but the devastating consequences of missed diagnosis mandate urgent evaluation 1

Disposition

• Immediate neurosurgical consultation if any red flag features are confirmed 1
• Urgent MRI within hours, not days, as surgical decompression within 48 hours of symptom onset provides best outcomes for cauda equina syndrome 1
• Patient should remain NPO pending neurosurgical evaluation 1