What is the diagnosis and management for a patient with absence of reflexes and a sensory level at lumbar 5 (L5)?

Diagnosis and Management of Absence of Reflexes with Sensory Level at L5

This clinical presentation is most consistent with cauda equina syndrome (CES) or lumbosacral plexopathy, and requires urgent MRI lumbar spine without IV contrast as the initial imaging study of choice, followed by immediate neurosurgical consultation if compression is confirmed. 1

Clinical Diagnosis

Key Diagnostic Features

• Absent lower limb reflexes with a sensory level at L5 strongly suggests cauda equina syndrome, which results from dysfunction of the sacral and lumbar nerve roots within the vertebral canal secondary to nerve root compression 1

• The most common cause of CES is lumbar disc herniation at the L4-L5 and L5-S1 levels, though other etiologies include neoplasm, infection/inflammation, spinal stenosis, and hemorrhage 1

• Critical red flag symptoms to assess immediately include:

  • Bladder, bowel, or sexual dysfunction 1
  • Perianal or saddle numbness 1
  • Back pain with or without radicular symptoms 1
  • Weakness in the lower limbs 1
  • Sensory changes or numbness in the lower limbs 1

Differential Diagnosis Considerations

• Lumbosacral plexopathy (L1-S4) causes weakness, sensory loss, and flaccid loss of tendon reflexes in the affected distribution 1

• The ankle jerk reflex is S1-mediated, while the patellar reflex is L4-mediated, helping to localize the lesion 2, 3

• L5 nerve root compression typically affects foot dorsiflexion and great toe extension, with sensory loss in the big toe and dorsal aspect of the foot 3

• Electrodiagnostic studies should be performed to confirm clinical diagnosis and differentiate radiculopathy from plexopathy, with needle EMG sensitivity reaching 90% for lumbosacral radiculopathy 2

Immediate Imaging

First-Line Imaging Study

• MRI lumbar spine without IV contrast is the imaging study of choice because of its ability to accurately depict soft-tissue pathology, assess vertebral marrow, and assess spinal canal patency 1

• A recent single 3-D heavily T2-weighted fat-saturated sequence protocol has been shown to be a rapid, highly sensitive tool for evaluating CES in the emergency department 1

• Urgent MRI assessment is recommended in all patients who present with new-onset urinary symptoms in the context of low back pain or sciatica 1

When to Add Contrast

• MRI lumbar spine without and with IV contrast may be helpful to delineate etiology of CES when underlying malignancy, infection, or inflammation is clinically suspected 1

• CT lumbar spine without IV contrast can answer the question of whether cauda equina compression is present when MRI is contraindicated or unavailable, though MRI is superior in soft-tissue contrast 1

Management Algorithm

Immediate Actions (Within Hours)

1. Perform focused neurological examination documenting:

   • Motor strength in all lower extremity muscle groups 1
   • Sensory level and distribution 1
   • Presence/absence of all lower extremity reflexes 1
   • Perianal sensation and rectal tone 1
   • Bladder function assessment 1

2. Order urgent MRI lumbar spine without IV contrast 1

3. Consult neurosurgery immediately if any red flag symptoms are present 1

Surgical Timing Considerations

• If CES is confirmed with spinal cord compression, surgical decompression should be performed as early as possible to optimize neurological recovery 1

• The majority of neurological recovery following spinal cord injury occurs during the initial 9-12 months, with a relative plateau reached by 12-18 months post-injury 4

• Early surgical intervention (within 96 hours) has been associated with improved outcomes in spinal cord injury patients 1

Common Pitfalls to Avoid

• Do not delay imaging while waiting for "conservative management" in patients with absent reflexes and sensory level findings, as this suggests significant neural compromise requiring urgent evaluation 1

• Do not assume the absence of bladder symptoms rules out CES, as back pain with radicular symptoms and absent lower limb reflexes are other important symptoms 1

• Do not confuse radiculopathy with plexopathy—electrodiagnostic studies are essential for differentiation 2

• The bulbocavernosus reflex has no prognostic value during acute evaluation and should not be used as a reliable marker for predicting neurological outcomes 5

Prognosis

• The most important determinant of prognosis is whether an injury is clinically complete or incomplete 4

• Recovery following incomplete injuries is particularly variable, with 20-75% of individuals recovering some degree of walking capacity by 1 year post-injury 4

• The presence of intramedullary hemorrhage and extended segments of edema on MRI have been associated with clinically complete spinal cord injury and worse prognosis 4