From the Guidelines
Sixth nerve palsy, also known as abducens palsy, should be evaluated and managed based on its underlying cause, with a focus on identifying and treating any serious underlying conditions, such as vasculopathic disorders, trauma, or neoplasms, as approximately 40% of patients with no recovery by 6 months may have a serious underlying pathology 1.
Clinical Presentation
The condition typically presents with an acute onset of horizontal double vision, worse at distance than at near and worse laterally toward the side of the affected nerve 1. Patients may also present with a head turn to compensate for the diplopia caused by the paralysis. The incomitant horizontal misalignment can result in disabling diplopia at onset, which may become more apparent with exhaustion or systemic illness, or in extreme horizontal gaze 1.
Causes and Diagnosis
The majority of acute 6th nerve palsies in the adult population are vasculopathic, associated with risk factors such as diabetes and hypertension 1. Other common causes include trauma and neoplasms 1. Diagnosis involves a complete neurological and ophthalmological examination, often supplemented by imaging studies like MRI or CT scans to evaluate for any underlying conditions 1.
Management
Treatment depends on the underlying cause 1. In microvascular cases, the condition often resolves spontaneously within 6 months 1. Temporary relief from diplopia can be achieved with prism glasses or patching one eye 1. For persistent cases, strabismus surgery may be considered 1. It's essential to identify and treat the underlying cause, particularly for non-microvascular etiologies, as sixth nerve palsy can sometimes indicate serious neurological conditions 1. Regular follow-up is crucial to monitor recovery and adjust treatment as needed 1.
From the Research
Causes of 6th Nerve Palsy
- Vascular diseases are the most commonly known causes of 6th nerve palsy after the age of 50 years 2
- Microvascular disease (hypertension or diabetes mellitus, or both) is present in 59% of patients with cranial nerve palsies, and of this group, 87% resolved spontaneously by 5 months rising to 95% by 12 months 3
- Diabetes mellitus, but not hypertension alone, is a risk factor for microvascular ischemic ocular motor cranial neuropathies 4
- In young adults (20 to 50 years of age), the most common cause for a sixth nerve palsy is a central nervous system (CNS) mass lesion, although the most common cause for an isolated sixth nerve palsy in this age group is multiple sclerosis 5
Incidence and Associations
- The age- and gender-adjusted annual incidence of sixth nerve palsy is 11.3/100 000 (95% confidence interval, 9.3-13.2/100 000) 6
- Causes and associations of sixth nerve palsy include: undetermined (26%), hypertension alone (19%), coexistent hypertension and diabetes (12%), trauma (12%), multiple sclerosis (7%), neoplasm (5%), diabetes alone (4%), cerebrovascular accident (4%), postneurosurgery (3%), aneurysm (2%), and other (8%) 6
Diagnosis and Management
- A lesion anywhere along the course of the nerve, from the pons to the orbit, can cause a paresis or palsy 2
- Cases should be classified into neurologically isolated or non-neurologically isolated cases, with neurologically isolated sixth nerve palsies associated most commonly with vascular disease 2
- Patients with clinically isolated single cranial nerve palsies associated with diabetes or hypertension are likely to recover spontaneously within 5 months and initially require observation only 3
- Non-neurologically isolated sixth nerve palsies typically are associated with more grave conditions, and patients with unexplained binocular diplopia and those who progress or fail to recover should be investigated to establish the underlying aetiology and managed as appropriate 3