From the Guidelines
The primary cause of abducens nerve palsy (Sixth Cranial Nerve Palsy) in adults is vasculopathic, associated with risk factors such as diabetes and hypertension, as stated in the 2024 study published in Ophthalmology 1.
Causes of Abducens Nerve Palsy
The causes of abducens nerve palsy can be categorized into several groups, including:
- Vasculopathic: associated with diabetes and hypertension, which is the most common cause in adults, as reported in the study 1
- Traumatic: resulting from head injury, typically involving a basilar skull fracture, or an acute rise in intracranial pressure from an intracranial bleed
- Neoplastic: caused by an intracranial neoplasm, which may be either insidious or acute
- Demyelinating diseases: such as multiple sclerosis, which can cause isolated cranial nerve VI palsy
- Postviral: which can occur after COVID-19 infection or post COVID-19 vaccination, although it is typically a diagnosis of exclusion
Clinical Presentation
The clinical presentation of abducens nerve palsy typically includes an acute onset of horizontal double vision, worse at distance than at near and worse laterally toward the side of the affected nerve, as described in the study 1. Patients may also present with a head turn to compensate for the diplopia caused by the paralysis.
Evaluation and Treatment
Evaluation for abducens nerve palsy should include a thorough neurological evaluation, including brain imaging (MRI or CT) to rule out serious underlying causes, especially if the palsy is accompanied by other neurological symptoms or occurs in younger patients without vascular risk factors 1. Treatment depends on the underlying cause, and temporary relief from double vision can be achieved using eye patches, prism glasses, or Botox injections into the medial rectus muscle. If the condition persists beyond 6-12 months, strabismus surgery may be considered to realign the eyes.
From the Research
Causes of Abducens Nerve Palsy
The causes of abducens nerve palsy, also known as sixth cranial nerve palsy, can be varied and include:
- Neurovascular compression (NVC) of the abducens nerve, which can be caused by a dolichoectatic basilar artery or other vascular structures 2, 3
- Ischemic stroke, which can cause bilateral abducens palsy without any other neurological deficit 4
- Head trauma, which can cause mechanical trauma to the orbit and lead to abducens nerve palsy 5
- Tumors, such as skull base tumors, which can compress the abducens nerve 4
- Aneurysms, which can compress the abducens nerve 4
- Orbital and/or facial injuries, which can affect the lateral rectus muscle directly or the orbital course of the abducens nerve and lead to palsy 5
Characteristics of Abducens Nerve Palsy
The characteristics of abducens nerve palsy can vary depending on the cause, but may include:
- Gradual onset of symptoms, such as diplopia and weakness of the lateral rectus muscle 2
- Sudden onset of symptoms, such as in the case of head trauma or ischemic stroke 4, 5
- Episodic symptoms, such as intermittent diplopia and weakness of the lateral rectus muscle 3
- Constant symptoms, such as persistent diplopia and weakness of the lateral rectus muscle 2, 3
Diagnosis and Treatment of Abducens Nerve Palsy
The diagnosis of abducens nerve palsy typically involves a combination of clinical evaluation, imaging studies, and laboratory tests. Treatment options may include:
- Microvascular decompression (MVD) for cases caused by neurovascular compression 2, 3
- Observation and conservative management for cases with gradual onset or episodic symptoms 2
- Surgical intervention for cases with orbital or facial injuries, or for cases with tumors or aneurysms compressing the abducens nerve 4, 5