From the Guidelines
The primary cause of 4th nerve palsy is head trauma, including concussion, which is one of the most common identifiable causes of both unilateral and bilateral acquired superior oblique palsy. According to the most recent study 1, head trauma is a leading cause of acquired 4th nerve palsy, resulting in weakness of the superior oblique muscle and creating a combination of vertical, torsional, and horizontal incomitant strabismus pattern. Other causes of 4th nerve palsy include:
- Congenital abnormalities, which may present with head tilt from childhood and facial asymmetry
- Compression from tumors, aneurysms, or inflammatory conditions, which can damage the nerve
- Less common causes such as multiple sclerosis, viral infections, and iatrogenic injury during neurosurgery
- Isolated trochlear schwannomas and giant cell arteritis, although these are extremely rare cases
It is essential to distinguish 4th nerve palsy from skew deviation, which has a similar motility pattern but is more frequently associated with less benign etiology and often warrants neuroimaging 1. Patients with 4th nerve palsy typically present with vertical diplopia (double vision) that worsens when looking down or to the side opposite the affected nerve, and may develop a compensatory head tilt. Diagnosis involves careful examination of eye movements, particularly when testing downward gaze with the eye adducted. Treatment depends on the underlying cause, ranging from observation for spontaneous recovery in traumatic or microvascular cases to surgical intervention for persistent symptoms.
From the Research
Causes of 4th Nerve Palsy
The causes of 4th nerve palsy can be varied, including:
- Congenital conditions, which are the most common cause of unilateral cases, accounting for 57.79% of cases 2
- Microvasculopathy, which accounts for 27.92% of unilateral cases, with symptoms typically resolving within 6 months 2
- Intracranial neoplasms, which account for 8.44% of unilateral cases 2
- Trauma, particularly closed head injury, which is the most common cause of bilateral cases, accounting for 75% of cases 2
- Ruptured arteriovenous malformation, which accounts for 25% of bilateral cases 2
- Cerebral aneurysms, which can also cause 4th nerve palsy, particularly those located in the internal carotid artery 3
Specific Causes and Their Characteristics
Some specific causes of 4th nerve palsy have distinct characteristics, such as:
- Microvasculopathy, which typically resolves within 6 months without the need for neuroimaging 2
- Cerebral aneurysms, which have a higher recovery rate with endovascular procedures compared to conservative management, particularly in ruptured aneurysms 3
- Trauma, which can cause bilateral 4th nerve palsy, particularly with closed head injury 2
Importance of Neuroimaging
Neuroimaging is not always necessary for patients with 4th nerve palsy, particularly those with microvasculopathy, but it should be considered in cases with atypical presentations, such as headache, periorbital pain, or rapid progression 2