Causes of Median Nerve Palsy
Median nerve palsy is most commonly caused by entrapment or compression at specific anatomical locations, particularly at the carpal tunnel, though it may also result from trauma, vascular abnormalities, or tumors affecting the nerve along its course.
Anatomical Considerations
The median nerve is vulnerable to compression or injury at several points along its course:
- Carpal tunnel: The most common site of median nerve compression
- Wrist: External compression or fractures
- Forearm: Trauma or compression
- Elbow: Entrapment or injury
- Upper arm: Less common site of injury
Common Causes of Median Nerve Palsy
Entrapment Neuropathies
- Carpal Tunnel Syndrome: The most frequent cause of median nerve palsy 1
- Characterized by compression of the median nerve at the wrist
- Often idiopathic but associated with repetitive hand movements
- Can be exacerbated by inflammation or fluid retention
Traumatic Causes
- Fractures: Particularly of the hamate hook 2
- Wrist trauma: Direct injury to the nerve
- Iatrogenic causes: Improper positioning during surgery or procedures 3
- Overextension of the wrist during surgical procedures
- Inappropriate fixation with holders or restraints
Vascular Causes
- Thrombosis of persistent median artery: A rare but documented cause 4
- Can present with symptoms similar to carpal tunnel syndrome
- Requires anticoagulation therapy
Inflammatory and Metabolic Causes
- Diabetes: Associated with increased risk of median nerve compression
- Growth factor abnormalities: Increased expression of:
- Transforming Growth Factor (TGF-β)
- Vascular Endothelial Growth Factor (VEGF)
- Interleukins 5
- Fibrotic changes: Increased collagen production and decreased matrix metalloproteinases
Neoplastic Causes
- Neurogenic tumors: Can directly affect the median nerve 1
- Space-occupying lesions: Tumors or cysts compressing the nerve
Diagnostic Approach
When evaluating median nerve palsy, imaging studies may be necessary:
- Ultrasound: First-line imaging for carpal tunnel and persistent median artery evaluation
- MRI: Confirms diagnosis and evaluates for space-occupying lesions
- Electrodiagnostic testing: Helps localize the site of compression or injury
Clinical Presentation
Patients typically present with:
- Numbness and tingling in the palmar aspect of digits 1-3
- Weakness of thumb opposition and abduction
- Pain or discomfort in the wrist or forearm
- Possible atrophy of thenar muscles in chronic cases
Management Considerations
Treatment depends on the underlying cause:
- Conservative management: Splinting, anti-inflammatory medications
- Surgical decompression: For severe carpal tunnel syndrome or other compressive lesions
- Anticoagulation: For vascular causes like persistent median artery thrombosis 4
- Anti-fibrotic therapy: May be beneficial in idiopathic cases 5
Early diagnosis and appropriate management are essential to prevent permanent nerve damage and optimize functional outcomes.