What is the likely cause of lower limb paralysis with intact reflexes, including knee jerk (KJ) reflex and ankle jerk (AJ) reflex, and preserved sensory function?

Spinal Cord Injury is the Most Likely Cause of Lower Limb Paralysis with Intact Reflexes and Preserved Sensation

The most likely cause of lower limb paralysis with intact knee jerk and ankle jerk reflexes and preserved sensory function is an incomplete spinal cord injury, specifically an anterior cord syndrome.

Pathophysiology and Clinical Presentation

Anterior cord syndrome is characterized by:

• Motor paralysis below the level of injury
• Preservation of deep tendon reflexes
• Intact sensory function, particularly proprioception and vibration sense
• Damage primarily to the anterior portion of the spinal cord

This pattern occurs because:

1. The anterior spinal cord contains the corticospinal tracts responsible for voluntary motor function
2. The reflex arcs that mediate deep tendon reflexes like knee jerk (KJ) and ankle jerk (AJ) are located in the spinal gray matter and remain intact
3. The posterior columns that carry sensory information (particularly proprioception and vibration) are preserved

Differential Diagnosis

1. Incomplete Spinal Cord Injury

• Anterior Cord Syndrome: Most consistent with the described presentation
• Central Cord Syndrome: Typically presents with greater weakness in upper extremities than lower extremities
• Brown-Séquard Syndrome: Would show ipsilateral motor weakness with contralateral sensory loss

2. Pure Motor Neuropathy

While pure motor neuropathy can present with motor weakness and preserved sensation, it typically causes reduced or absent reflexes rather than intact reflexes 1.

3. Todd's Paralysis

Todd's paralysis is a post-seizure phenomenon that can cause transient weakness, but:

• It's typically unilateral (though rare bilateral cases exist) 2, 3
• Usually resolves within minutes to hours 4
• Is often associated with old stroke as an etiology 5

4. Peripheral Artery Disease (PAD)

Acute limb ischemia can cause paralysis, but:

• Would typically present with other signs like pain, pallor, pulselessness, poikilothermia, and paresthesias 6
• Would affect sensory function
• Class III (irreversible) acute limb ischemia includes complete sensory loss and motor function loss 6

Diagnostic Approach

1. Urgent MRI of the spine: This is the gold standard for diagnosing spinal cord injury 6

   • Focus on identifying compression, edema, or signal changes in the spinal cord
   • Pay particular attention to the anterior portion of the cord

2. Additional neurological examination:

   • Test for sacral sparing (perianal sensation and voluntary anal contraction)
   • Assess for a sensory level
   • Evaluate for signs of cauda equina syndrome (saddle anesthesia, bowel/bladder dysfunction) 6

3. Consider vascular assessment if there's concern for ischemic etiology:

   • Ankle-brachial index (ABI)
   • Arterial Doppler studies

Management Considerations

1. Timing of surgical intervention is critical in spinal cord injury:

   • Early decompression (within 24-48 hours) may improve neurological outcomes 6
   • Delayed surgery may result in poorer recovery of motor function

2. Medical management:

   • Methylprednisolone may be considered in acute spinal cord injury within 8 hours
   • Blood pressure management to maintain adequate spinal cord perfusion
   • Prevention of secondary injury

3. Rehabilitation:

   • Early mobilization and physical therapy
   • Prevention of complications (DVT, pressure ulcers, respiratory complications)

Key Pitfalls to Avoid

1. Misdiagnosing as stroke: The presence of intact reflexes and preserved sensation makes stroke less likely.

2. Delaying imaging: Urgent MRI is essential to identify potentially reversible causes of cord compression.

3. Overlooking vascular etiologies: In older patients or those with vascular risk factors, consider acute limb ischemia, though the preservation of sensation makes this less likely 6.

4. Failing to recognize progressive neurological deterioration: Monitor for signs of ascending cord involvement or respiratory compromise.

The combination of lower limb paralysis with preserved reflexes and intact sensation strongly points to an incomplete spinal cord injury affecting the anterior cord. Prompt diagnosis and appropriate management are crucial for optimizing neurological recovery.