Reperfusion injury.

Context

Intraoperative neurophysiological monitoring (IONM), particularly TcMEPs, is a key tool during spinal cord surgeries like posterior cervical decompression. It provides real-time feedback about the functional integrity of motor pathways.

In patients with cervical myelopathy, the spinal cord is chronically compressed and ischemic. When decompression is performed, a reperfusion injury may occur, and TcMEPs can show early signs of this.

⚡ TcMEPs: What They Measure

• TcMEPs are recordings of motor pathway responses following electrical stimulation of the motor cortex.
• Reflect descending corticospinal tract function.
• Sensitive to ischemia, injury, or disruption of spinal cord motor pathways.

TcMEP Changes Suggestive of Reperfusion Injury

📉 Sudden Loss or Decrease in Amplitude

• Abrupt drop or loss in TcMEP amplitude immediately after decompression.
• May occur without mechanical cause (no hematoma, no compression on imaging).

🧠 No Change in SSEPs

• Somatosensory evoked potentials (SSEPs) may remain unchanged, supporting a motor-specific spinal cord injury (common in reperfusion injury).

⏱️ Timing

• Changes often occur shortly after decompression when perfusion is restored to chronically ischemic spinal cord tissue.
• There may be a “paradoxical” loss: the patient had stable signals during compression, but signals degrade after decompression.

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⚠️ Differential Diagnosis of TcMEP Loss Post-Decompression

Cause	Features	TcMEPs	SSEPs
Reperfusion injury	After decompression, no mechanical cause	↓ or lost	Normal
Epidural hematoma	May occur later	↓ or lost	↓
Vascular compromise (e.g., anterior spinal artery)	May be sudden	↓ or lost	Normal/↓
Technical issues	Sudden and global changes	↓ or lost	↓ or lost

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🧬 Pathophysiology Link

• The ischemic spinal cord is highly vulnerable to free radical and cytokine-induced damage during reperfusion.
• TcMEP loss reflects dysfunction in corticospinal tract neurons, which are particularly susceptible.

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🛠️ Clinical Implications

🚨 What to Do Intraoperatively:

1. Immediately rule out mechanical causes (check for hematoma, hardware).
2. Maintain mean arterial pressure (MAP > 85-90 mmHg) to ensure spinal cord perfusion.
3. Administer high-dose steroids (controversial but often considered).
4. Neuromonitoring team should document changes, and surgical team may halt or reverse decompression if needed.

🩺 Postoperative:

• MRI to assess for cord edema or infarct.
• Monitor neurologic function closely.
• Initiate rehabilitation early if deficits persist.

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📊 Summary Table

Parameter	Reperfusion Injury
Timing	Immediately after decompression
TcMEP	Sudden drop or loss
SSEP	Usually unchanged
Imaging	Cord edema on T2-weighted MRI
Management	BP support, steroids, ICU care

Overview

What is Reperfusion Injury?

Reperfusion injury refers to cellular and tissue damage caused when blood supply returns to the tissue after a period of ischemia (lack of oxygen). The return of blood can cause inflammation and oxidative damage through the production of free radicals.

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Pathophysiology in Cervical Myelopathy Surgery

Chronic Compression and Ischemia

• In cervical spondylotic myelopathy, the spinal cord experiences chronic compression, leading to reduced blood flow, metabolic stress, and ischemic changes.
• Over time, the spinal cord adapts to this hypoxic environment.

Decompression and Sudden Reperfusion

• During posterior cervical decompression (e.g., laminectomy, laminoplasty), there’s a sudden restoration of blood flow to previously ischemic regions of the spinal cord.
• This reperfusion can cause:
  • Oxidative stress (from reactive oxygen species)
  • Inflammation
  • Edema
  • Disruption of the blood-spinal cord barrier
  • Neuronal and glial cell injury

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Clinical Presentation

Timing

• Symptoms typically present immediately or within hours after surgery.

Symptoms

• Worsening neurological function after an initially uneventful decompression.
• New or increased motor weakness, sensory deficits, or even paralysis.
• May present with no mechanical cause (e.g., hematoma or hardware compression on imaging).

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Diagnosis

Imaging

• MRI may show:
  • T2 hyperintensity in the spinal cord (suggestive of edema).
  • No new compressive lesion.

Rule Out Other Causes

• Rule out surgical complications:
  • Epidural hematoma
  • Hardware malposition
  • Residual compression

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Management

Medical Management

• High-dose steroids (e.g., methylprednisolone) may be used to reduce inflammation and edema.
• Close monitoring in an ICU setting.

Supportive Care

• Maintain spinal cord perfusion (adequate blood pressure).
• Physical therapy and rehabilitation if motor function is impaired.

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Prevention and Considerations

Preoperative

• Preoperative MRI signal changes (e.g., T2 hyperintensity) can indicate higher risk of reperfusion injury.

Intraoperative

• Gentle decompression techniques.
• Gradual decompression may theoretically reduce risk (though difficult in practice).

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Prognosis

• Variable: Some patients may recover completely, while others have permanent neurological deficits.
• Early recognition and treatment are critical to improving outcomes.

https://pmc.ncbi.nlm.nih.gov/articles/PMC11394496

https://neurointraoperative.com/wp-admin/post.php?post=1849&action=edit

Stimulating and Recording parameters while recording Motor evoked potentials in cervical cord compressive myelopathy.