Can a C3 (cervical spine level 3) injury cause unilateral lid lag?

C3 Injury and Unilateral Lid Lag: Neuroanatomical Considerations

A C3 spinal injury alone does not typically cause unilateral lid lag, as lid function is primarily controlled by cranial nerves rather than cervical spinal segments. 1

Neuroanatomy of Eyelid Control

Eyelid function is primarily controlled by:

• Levator palpebrae superioris muscle: Innervated by the oculomotor nerve (CN III), which originates from the midbrain, not the cervical spine 2
• Müller's muscle: Innervated by sympathetic fibers that originate in the hypothalamus and travel through the cervical sympathetic chain
• Orbicularis oculi muscle: Innervated by the facial nerve (CN VII), which originates from the pons

Potential Mechanisms for Lid Lag After Cervical Injury

1. Sympathetic Pathway Disruption:

   • The cervical sympathetic chain runs alongside the cervical vertebrae
   • Damage to C3 could potentially affect sympathetic innervation to the eye
   • However, this would typically cause Horner's syndrome (ptosis, miosis, anhidrosis) rather than lid lag 2

2. Brainstem Involvement:

   • If a C3 injury extends to affect the brainstem, it could potentially impact cranial nerve nuclei
   • This would be an indirect effect of the injury, not directly from C3 damage 3

3. Associated Traumatic Brain Injury:

   • Many cervical spine injuries occur with concurrent head trauma
   • TBI can cause various ocular motility disorders including lid abnormalities 4

Differential Diagnosis for Unilateral Lid Lag

When encountering unilateral lid lag in a patient with C3 injury, consider these more likely causes:

1. Thyroid Eye Disease: Most common cause of lid lag 2
2. Myasthenia Gravis: Can present with variable ptosis and lid lag 2
3. CN III (Oculomotor) Palsy: May cause lid abnormalities along with other ocular motility problems 2
4. Traumatic Brain Injury: Can cause various ocular motor deficits 4
5. Dorsal Midbrain Syndrome: Can cause lid retraction and other ocular abnormalities

Evaluation Approach

For a patient with C3 injury and unilateral lid lag:

1. Complete neuro-ophthalmologic examination:

   • Assess pupillary responses (normal in isolated lid lag, abnormal in CN III palsy) 2
   • Check for fatigability (present in myasthenia gravis) 2
   • Evaluate for other ocular motility abnormalities

2. Imaging:

   • MRI of brain and cervical spine to assess for extension of injury to brainstem 1
   • CT angiography if vertebral artery injury is suspected 2

3. Laboratory testing:

   • Thyroid function tests (TSH, T3, T4)
   • Acetylcholine receptor antibodies if myasthenia gravis is suspected 2

Conclusion

While C3 spinal cord injury can cause numerous neurological deficits, unilateral lid lag is not typically a direct consequence of isolated C3 injury. When encountering this combination, clinicians should investigate for concurrent conditions affecting the oculomotor system or sympathetic pathway, or consider that the lid lag may be unrelated to the C3 injury.

The presence of unilateral lid lag in a patient with C3 injury should prompt a thorough evaluation for alternative etiologies, particularly those affecting cranial nerve function or representing concurrent traumatic brain injury.