Fourth nerve palsy

Background

Right eye

Eye movements by extra-ocular muscles and cranial nerve innervation

• Also called CN IV or trochlear nerve palsy
• Trochlea innervates superior oblique muscle
  • Intorts, depresses and abducts the globe
• Trochlear nerve palsy causes an inability to move the eye in inward rotation, downward, and laterally.
• Most common cause of vertical diplopia

Etiology

• Head trauma
• Mechanisms that increase intraocular pressure
  • Practically never caused by aneurysm
• Herpes zoster ophthalmicus
• Meningitis
• Diabetic neuropathy
• Lupus/Sjögren syndrome

Clinical Features

• Vertical, torsional, or oblique diplopia.
  • Worse on downward gaze and gaze away from affected muscle
• Head-tilt
  • Tilt typically away from affected side (~70%) to overcome inward rotation of affected eye to create wider separation of images. Can be paradoxical, where patient tilts head toward affected side (~3%)
  • Bielschowsky phenomenon - head tilt to affected side reveals inability to intort, diplopia

Differential Diagnosis

• Increased intracranial pressure (ICP): Pseudotumor cerebri
• Vascular: Stroke, subarachnoid hemorrhage, aneurysm (extremely rare), microvasculopathy from diabetes, atherosclerosis or hypertension
• Neoplastic: Tumor in the subarachnoid space
• Degenerative/deficiency: Vitamin B12 deficiency, Wernicke-Korsakoff syndrome
• Idiopathic: Most common cause of acquired trochlear nerve palsy.
• Infection: Meningitis, herpes zoster
• Congenital: Dysgenesis of trochlear nerve nucleus or abnormal peripheral nerve
• Autoimmune: Myasthenia gravis, multiple sclerosis, systemic lupus erythematosus, giant cell arteritis, Sjögren
• Trauma: Its long course makes it susceptible to traumatic injury. Head trauma (adult) is the second most common cause. Is generally severe with loss of consciousness. Consider underlying structural abnormalities if results after minor trauma.
• Endocrine: Thyroid ophthalmopathy
• Third nerve palsy
• Abducens nerve palsy

Evaluation

Labs and Tests

• +/- POC glucose, CBC, and other labs depending on suspected diagnosis
• +/- LP after negative neuroimaging if suspect subarachnoid hemorrhage or meningitis.

Imaging

• Head CT if traumatic, suspect stroke, or subarachnoid hemorrhage (rare).
• MRI is study of choice, although there no increased yield from MRI vs CT scan.

Management

• Address underlying acute pathology
• May require surgical correction
• +/- Neurology consult

Disposition/Follow-up

• Vasculopathic: Observation for improvement over 6-8 weeks. Often resolve spontaneously in 4-6 months.
• Traumatic: Observation for improvement over 6-8 weeks. Often resolves spontaneously. If progressing or lack of improvement – neuroimaging with MRI
• Isolated, idiopathic cases very rarely have an underlying etiology after prolonged follow-up, and most resolve spontaneously in weeks to months. If no improvement in 2 months, consider neuroimaging.

See Also

• Ocular palsy
• Cranial nerves

External Links

• Medscape: Trochlear Nerve Palsy