What is the likely diagnosis and urgent management for a 28-year-old woman with two months of low back pain, new urinary retention, lower limb weakness (3/5), upper limb strength 4/5, and loss of vibration and touch sensation?

Cauda Equina Syndrome – Diagnosis and Urgent Management

Immediate Diagnosis

This patient has cauda equina syndrome with retention (CESR), evidenced by urinary retention, bilateral lower extremity weakness (3/5), upper extremity weakness (4/5), and loss of vibration/touch sensation – she requires emergency MRI of the lumbar spine and immediate neurosurgical consultation for decompressive surgery within 12 hours. 1

The clinical presentation is unequivocal:

• Urinary retention demonstrates 90% sensitivity for established cauda equina syndrome and represents a late "white flag" sign indicating irreversible neurological damage has already begun 2, 1
• Bilateral lower extremity weakness (3/5) with upper extremity involvement (4/5) indicates extensive cauda equina compression with ascending involvement 1
• Loss of vibration and touch sensation confirms significant sensory pathway compromise 1
• Two-month progression from back pain to retention is consistent with the gradual development of non-traumatic cauda equina syndrome, which typically evolves over weeks to months 1

Critical Staging and Prognosis

This patient has progressed to Cauda Equina Syndrome with Retention (CESR), the most advanced stage:

• Patients at the CESR stage have variable recovery even with urgent surgery – only 48-93% achieve any improvement 1
• Many will require lifelong intermittent catheterization, manual fecal evacuation, and experience loss of sexual function 1
• Contrast this with earlier stages: patients treated at the incomplete stage (CESI) achieve normal or socially normal bladder/bowel function, while those treated at the suspected stage (CESS) have complete prevention of cauda equina syndrome 1

Emergency Diagnostic Protocol

Perform emergency MRI of the lumbar spine without IV contrast immediately – this is the gold standard with 96% sensitivity and 94% specificity for cauda equina pathology 1

• MRI must be performed within 1 hour of suspicion being raised, regardless of time of day 3
• Do not delay MRI for laboratory tests or other ancillary studies 1
• CT scan alone is inadequate – it has only 6% sensitivity for neural compression and cannot visualize the cauda equina nerve roots, epidural space, or degree of compression necessary for surgical planning 1

Do not catheterize before assessing post-void residual volume, as this obscures whether the patient is in CESI versus CESR stage 1

Surgical Timing

Emergency decompressive surgery should be performed within 12 hours when feasible 1

• Outcomes are superior when decompression occurs within 12-72 hours compared with later intervention 1
• Neurological deterioration can occur rapidly and is associated with long-term poor outcomes 3
• It is not possible to predict which patients will deteriorate neurologically nor how rapidly 3
• Damage to cauda equina nerve roots occurs in a continuous and progressive fashion – there are no safe time thresholds 3

Differential Diagnosis Considerations

While cauda equina syndrome from disc herniation is most likely (>90% of symptomatic lumbar disc herniations occur at L4/L5 or L5/S1 levels 4), the MRI will also evaluate for:

• Spinal epidural abscess – particularly important given the two-month duration; average time to diagnosis of vertebral osteomyelitis is 2-4 months 5
• Spinal cord tumor or metastatic disease – consider given age and progressive course 1
• Massive midline disc herniation – the most common cause of cauda equina syndrome, occurring in approximately 0.04% of patients with low back pain 2, 1

Critical Pitfalls to Avoid

• Do not wait for complete saddle anesthesia or fecal incontinence – these are late signs of irreversible damage 1
• Do not rely on rectal tone assessment – it has low interobserver reliability, especially among inexperienced clinicians 1
• Do not delay referral because symptoms have been present for two months – even delayed decompression can provide significant improvement, though outcomes are worse than early intervention 6
• Do not order CT instead of MRI – CT cannot adequately visualize the intraspinal contents or nerve root compression that defines cauda equina syndrome 1

Expected Outcome

Given this patient's presentation at the CESR stage with established urinary retention:

• She has likely already sustained some irreversible neurological damage 1
• Aggressive surgical decompression within 12-24 hours offers the best chance for recovery, though complete return to normal function is unlikely 1
• Pre-operative preservation of any perineal sensory function predicts higher likelihood of postoperative recovery 1