Sixth nerve palsy

Background

Figure showing the mode of innervation of the recti lateralis from CNII.

Right eye

Eye movements by extra-ocular muscles and cranial nerve innervation

• Also called 6th cranial nerve (CN VI) or abducens nerve palsy
• Most common ocular nerve palsy
• Innervates the ipsilateral lateral rectus muscle controlling eye abduction
• Esotropia (eye moves inward) of the affected eye due to the unopposed action of the medial rectus muscle, innervated by the oculomotor nerve (CN III)

Causes

• Nuclear lesion
  • Congenital, demyelinating, ischemia, traumatic
• Inflammatory
  • Vasculitis
  • Sarcoidosis
  • Systemic lupus erythematosus
• Infectious
  • Lyme disease
  • Syphilis
  • Tuberculosis
  • Meningitis
• Orbital lesions
  • Neoplastic
  • Inflammatory
  • Infectious

Clinical Features

Limitation of abduction of the right eye when looking to the right.

Paresis of the abducens nerve (demonstrated in the right eye when looking to the right).

History

• May complain of:
• Diplopia (frequent complaint) upon attempting lateral gaze and esotropia at rest
  • May have a head turn to help correct their diplopia
• Vision loss
• Hearing loss
• Symptoms of vasculitis, most commonly giant cell arteritis (headache, tenderness of the scalp, jaw claudication, reduced visual acuity, tinnitus, fever_
• +/- history of diabetes, hypertension, stroke, fever, and headache

Examination

• Excluding paresis of the other cranial nerves
• Check ocular muscle movements
• Check for papilledema
• Test pupillary response
• Test ocular motor nerves (CN III, IV, and VI)
  • Trace a full H-pattern with finger and have the patient follow the finger only with their eyes
  • Patients with abducens nerve palsy are unable to move the affected eye laterally
  • In order to avoid diplopia, patients will turn their heads away from the lesion so that both eyes are looking sideways
  • Check deep tendon reflexes and strength to exclude corticospinal tract involvement

Differential Diagnosis

• Increased intracranial pressure (ICP): Because of its position and intracranial length, increased ICP from any cause can lead to injury and dysfunction
• Vascular: Aneurysm, central venous sinus thrombosis
• Inflammatory: Post-viral, demyelinating, sarcoidosis, giant cell arteritis, Miller-Fisher Syndrome variant of Guillian-Barre Syndrome
• Neoplastic: Lesions in the cerebellopontine angle. In children – pontine glioma
• Degenerative/deficiency: Vitamin B deficiency, Wernicke-Korsakoff syndrome
• Iatrogenic: Post-lumbar puncture, status-post surgery involving head
• Infection: Meningitis, lyme disease, syphilis
• Congenital: Rare to find true congenital sixth nerve palsy
• Autoimmune: Myasthenia Gravis
• Trauma: Especially if a torsional head motion or medial wall orbital fracture (with entrapment of the medial rectus muscle
• Endocrine: Diabetic cranial mononeuropathy - the incidence of palsy in the 3rd, 6th, and 7th cranial nerves is significantly higher in patients with diabetes

Evaluation

Work-up

• Workup will depend on suspected etiology, may include
  • POC glucose
  • CBC
  • BMP
  • ESR
  • Lyme titer
  • RPR (if suspect syphilis)
  • Lumbar puncture to exclude meningitis, Guillain-Barré
  • Antinuclear antibody test
  • CT head: exclude acute bleed or mass
  • MRI: indicated for brainstem findings on the exam and to exclude pontine glioma in children and in adults where the abducens nerve palsy does not improve

Management

• Treat by underlying etiology
• Consider neuro/optho consult
• Children: Can be treated with alternating patching to decrease probability of developing amblyopia in the affected eye
• Adults: Lenses can be fogged with clear tape, paint, or nail polish to decrease diplopia. Neurology can prescribe Fresnel prisms as an alternative.
• Giant cell arteritis: treat with prednisone or intravenous Methylprednisolone.

Disposition

• Dispo appropriate to etiology
• Truly isolated cases: often benign, can be followed up by neurologist for serial exams
• Surgery: If patient does not improve within 6 months after treatment and serial check-ups, surgery may be required

See Also

• Ocular palsy
• Cranial nerves