From the Guidelines
Bilateral sixth nerve palsy is most commonly caused by increased intracranial pressure, which compresses both abducens nerves as they travel along the base of the skull, as supported by the most recent study 1. The causes of bilateral sixth nerve palsy can be diverse and include:
- Increased intracranial pressure due to conditions such as brain tumors, hydrocephalus, idiopathic intracranial hypertension, or meningitis
- Vascular disorders like diabetes mellitus, hypertension, and atherosclerosis, which damage the blood supply to the nerves
- Demyelinating diseases such as multiple sclerosis, which can affect the nerve sheaths
- Infectious processes including Lyme disease, syphilis, and viral infections, which may directly impact the nerves
- Trauma, particularly basilar skull fractures or severe head injuries, which can damage both nerves simultaneously
- Inflammatory conditions like sarcoidosis and systemic lupus erythematosus, which may cause bilateral involvement
- Certain medications, particularly chemotherapeutic agents like vincristine and cisplatin, which can be toxic to the nerves
- Wernicke's encephalopathy from thiamine deficiency and metastatic infiltration of the skull base, which are additional potential causes As noted in 1, the majority of acute sixth nerve palsies in the adult population are vasculopathic, associated with risk factors such as diabetes and hypertension, and most palsies resolve after 6 months. However, if no recovery is apparent by 6 months, approximately 40% of patients demonstrate a serious underlying pathology warranting further evaluation, as mentioned in 1. Given the potential for serious underlying conditions, any patient presenting with bilateral sixth nerve palsy requires urgent neuroimaging and comprehensive evaluation to identify the underlying cause, as this presentation often indicates serious neurological conditions, as emphasized in 1.
From the Research
Causes of Bilateral Sixth Nerve Palsy
- Head trauma: Bilateral sixth nerve palsy can occur after head trauma, as reported in a case study where a patient experienced transient bilateral abducens nerve palsy after minor head trauma 2.
- Increased intracranial pressure: The appearance of bilateral sixth-nerve palsy is usually a harbinger of serious intracranial disease or a nonspecific sign of increased intracranial pressure from any cause 3.
- Cerebrospinal fluid abnormalities: Cerebrospinal fluid abnormalities were more frequent among bilateral sixth nerve palsy cases, suggesting a possible cause 4.
- Water-soluble contrast myelography: Bilateral sixth-nerve palsy can be a complication of water-soluble contrast myelography, although this is rare and usually self-limiting 3.
- Traumatic brain injury: Traumatic brain injury can cause elevated intracranial pressure, which may lead to bilateral sixth nerve palsy, as suggested by a study on the correlation between computed tomography findings and measured intracranial pressure in patients with moderate to severe traumatic brain injury 5.
- Other causes: Other possible causes of bilateral sixth nerve palsy include myasthenia, orbital muscle entrapment, convergence spasm, divergence palsy, and pretectal pseudoconvergence, although these are less common 4.
Clinical Presentation and Diagnosis
- Diplopia: Bilateral sixth nerve palsy can cause diplopia, which may be related to anatomical lesions, even if the diplopia is transient 2.
- Gaze deficits: Gaze deficits are not uncommon after head trauma and might be caused by injury to the central nervous system, the peripheral nerve, or the motor unit 6.
- Imaging studies: Imaging studies such as computed tomography (CT) scans can help diagnose and manage bilateral sixth nerve palsy, as well as identify potential causes such as increased intracranial pressure or traumatic brain injury 2, 5.