Cranial Nerve IV Palsy

Cranial Nerve IV Palsy
SYMPTOMS Vertical diplopia that gets worse when reading or when tilting head towards the side of the palsy
A horizontal phoria can manifest due to vertical dissociation
SIGNS Typically unilateral
EOM restriction when looking down and in, Head tilt opposite the side of the palsy, Hyperdeviation that gets worse when looking opposite to the eye with the palsy and when tilting head to the same side to the eye with the palsy, Chin tucked downward
WORK-UP Pupils | EOMs | Cover test | Complete eye exam with dilation | Cranial nerve testing | Park’s 3 step | Maddox rod | Vertical fusional vergences | Forced duction testing
TREATMENT If cranial nerve IV palsy is acute onset and due to trauma, the patient should be referred to a neuro-ophthalmologist/neurologist/PCP/ER ASAP to rule out a subarachnoid hemorrhage
Children or Adults under the age of 50 years old with an acute onset CN IV palsy should be referred to a pediatric ophthalmologist/pediatrician/neuro-ophthalmologist/neurologist/PCP/ER ASAP
Adults over the age of 50 years old with an acute onset CN IV palsy can be observed and referred to their PCP for a vascular work-up, but strong consideration should be given to referring patient to a neuro-ophthalmologist/neurologist/PCP/ER if there is no improvement within 1 month, if there is progression, if there is aberrant regeneration, or if there are other neurological symptoms
Longstanding congenital or decompensating CN IV palsies can be monitored
Fresnel prisms can temporarily help with diplopia with acute onset CN IV palsies
Vertical prism can be put in glasses if there is decompensation of a CN IV palsy
Treatment depends on the underlying etiology of the CN IV palsy
FOLLOW-UP Monitor monthly until complete resolution
ADDITIONAL LAB | TESTS Neuro-imaging is typically ordered through neuro-ophthalmologist/neurologist/PCP/pediatric ophthalmologist/pediatrician/ER and may include the following: MRI of the brain with and without contrast | CT of the brain with and without contrast | MRA | CTA
If etiology is suspected to be due to vascular ischemia, the following should be ordered through the patient’s PCP: Blood pressure evaluation | Fasting blood sugar | HbA1c | CBC with differential | ESR | C-reactive protein | ANA
ETIOLOGY Cranial nerve IV damage can be secondary to the following:
Vascular ischemia from systemic diseases such as diabetes
Trauma (Cranial nerve 4 is susceptible to trauma since it is the only nerve to exit the dorsal aspect of brainstem and travel through the subarachnoid space)
Compression from a tumor or aneurysm (Rare)
Infiltrative
Congenital due to incomplete development of the nucleus or nerve (Most common cause)
DIFFERENTIAL DX Cranial nerve III palsy, Orbital pseudotumor, Brown syndrome, Internuclear ophthalmoplegia, Myasthenia gravis, Thyroid eye disease, Chronic progressive external ophthalmoplegia
NOTES As a patient gets older, sudden diplopia could also occur due to EOM decompensation or a congenital cranial nerve 4 palsy (Patients with a decompensated cranial nerve palsy will present with a compensatory head tilt, large vertical fusional vergences, and large hypertropia in the primary position)
A bilateral CN IV palsy should be suspected if there is alternating hypertropia on changes in tilt or horizontal gaze, large degree of excyclotorsion greater than 10 degrees, small hypertropia in primary gaze, and underaction of both superior obliques

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