Abducens nerve palsy

Background

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

Clinical Features

History

Patient with abducens nerve palsy may complain of:

• Frequently present with diplopia 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 acutity, tinnitus, fever
• Ask about 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 thrombosis
• Inflammatory: Post-viral, demyelinating, sarcoid, 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 syndrom
• Idiopathic: 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

• POC glucose
• CBC
• BMP
• ESR
• Lyme Titer
• RPR (If suspect syphilis)
• Lumbar puncture with cerebrospinal fluid analysis indicated to exclude meningitis
• Antinuclear antibody test
• CT head: before LP to 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

• See Examination above
• Complete neuro exam

Management

• True isolated cases: often do not need specific treatment
• Children: Can be treated with alternating patching to decrease probability of developing amblyopia in the affected eye
• Giant cell arteritis: treat with prednisone or intravenous Methylprednisolone.

Disposition

• Dispo appropriate to etiology, consult either Neuro or Ophtho
• True isolated cases: often benign; can be followed up by neurologist for serial exams
• Adults: Lenses can be fogged with clear tape, paint, or nail polish to decrease diplopia. Neurology can prescribe Fresnel prisms as an alternative.
• 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

References

Authors

Samantha Sales, Stephen Bogh, Neil Young, Michael Holtz, Ross Donaldson, Daniel Ostermayer, Daniel Eggeman