Which specialty treats a 6th (sixth) cranial nerve palsy?

Management of Sixth Cranial Nerve Palsy

A sixth cranial nerve palsy should primarily be evaluated and managed by an ophthalmologist, specifically a neuro-ophthalmologist, with potential referral to neurology depending on the underlying etiology. 1

Diagnostic Approach

The sixth cranial nerve (abducens nerve) controls the lateral rectus muscle, which is responsible for abducting the eye. When paralyzed, patients typically present with:

• Horizontal diplopia (double vision), worse at distance than near
• Incomitant esotropia (eye turns inward)
• Compensatory head turn toward the affected side
• Limited or absent abduction of the affected eye

Initial Evaluation by Ophthalmologist

The ophthalmologist should perform:

1. Complete ophthalmic examination with emphasis on:

   • Best-corrected visual acuity
   • Check for afferent pupillary defect
   • Color vision assessment
   • Sensorimotor examination documenting the esotropia pattern
   • Fundus examination for papilledema or optic atrophy 1

2. Detailed medical history focusing on:

   • Prior ocular surgery
   • Vascular risk factors (diabetes, hypertension)
   • Associated symptoms (facial weakness, headache, proptosis) 1

Referral Algorithm

Immediate Referral to Neurology/Neurosurgery

Urgent neurological consultation is needed when:

• Patient is young (under 50)
• Multiple cranial nerve involvement
• Neurological deficits beyond the sixth nerve
• Signs of increased intracranial pressure
• No vascular risk factors
• Bilateral sixth nerve palsies 1

Referral to Neuro-ophthalmologist

Indicated for:

• Persistent palsy beyond 4-6 weeks
• Uncertain diagnosis
• Need for specialized treatment
• Elderly patients with temporal artery tenderness or jaw claudication (possible giant cell arteritis) 1

Management Pathway

Diagnostic Testing

1. Neuroimaging:

   • MRI brain with contrast for all young patients
   • MRI for older patients with atypical features or no improvement after 4-6 weeks
   • Focus on brainstem, subarachnoid space, cavernous sinus, and orbit 1

2. Laboratory tests when indicated:

   • Blood pressure, glucose, HbA1c for suspected vasculopathic causes
   • ESR and CRP for suspected giant cell arteritis
   • Lumbar puncture if meningeal signs or increased intracranial pressure 1

Treatment Approach

1. Initial Management:

   • Treatment of underlying cause
   • Observation for mild symptoms or if patient declines intervention
   • Temporary occlusion (patch, Bangerter filter) for symptomatic diplopia 1

2. Nonsurgical Options:

   • Prism glasses (temporary or ground-in) if stable deviation
   • Botulinum toxin injection to medial rectus to prevent contracture 1

3. Surgical Management:

   • Consider after 6 months if palsy persists
   • Options based on residual lateral rectus function:
     • With some function: medial rectus recession with lateral rectus resection
     • Without function: vertical rectus transposition procedures 1

Prognosis

• 85% show at least partial recovery
• 67% achieve complete recovery
• Better outcomes with smaller initial deviation angles 2
• Most vasculopathic cases resolve within 6 months
• Neoplastic causes have lower spontaneous recovery rates 1, 3

Common Pitfalls to Avoid

1. Assuming vasculopathic cause in young adults

   • In patients under 50, CNS mass lesions and multiple sclerosis are common causes 3
   • Always consider neuroimaging in young patients

2. Delaying evaluation for giant cell arteritis

   • In elderly patients with headache, scalp tenderness, or jaw claudication
   • Requires immediate ESR/CRP and potential temporal artery biopsy 1

3. Missing increased intracranial pressure

   • Bilateral sixth nerve palsies often indicate increased intracranial pressure
   • Check for papilledema and consider lumbar puncture after neuroimaging 1

4. Premature surgical intervention

   • Most cases improve within 6 months
   • Surgery should be deferred until stability is confirmed 1

By following this approach, clinicians can ensure appropriate evaluation and management of sixth cranial nerve palsy, optimizing outcomes for morbidity, mortality, and quality of life.