From the Guidelines
The most common causes of 6th nerve palsy are vasculopathic, traumatic, and neoplastic in nature, with vasculopathic being the most prevalent, particularly in patients with diabetes and hypertension 1. The sixth cranial nerve (abducens nerve) palsy has multiple causes, including:
- Vascular diseases, such as those associated with diabetes mellitus, hypertension, or atherosclerosis, where microvascular ischemia affects the nerve 1
- Trauma, which can damage the nerve directly or cause compression from bleeding or swelling 1
- Neoplasms, especially those at the base of the skull or in the cavernous sinus, which can compress the nerve 1
- Infections, such as meningitis, encephalitis, or Lyme disease, which may lead to nerve inflammation 1
- Inflammatory conditions, including multiple sclerosis, sarcoidosis, and vasculitis, which can also cause sixth nerve palsy 1
- Demyelinating diseases, such as multiple sclerosis, which can cause isolated cranial nerve VI palsy, particularly in adults 1 The anatomical vulnerability of the abducens nerve contributes to its susceptibility to injury, as it has the longest intracranial course of all cranial nerves, making it vulnerable to stretching and compression 1. It is essential to evaluate patients with 6th nerve palsy for underlying serious pathology, particularly if no recovery is apparent by 6 months, as approximately 40% of patients may demonstrate a serious underlying condition warranting further evaluation 1.
From the Research
Causes of 6th Nerve Palsy
The causes of 6th nerve palsy can be varied and include:
- Vasculopathic conditions such as diabetes mellitus, hypertension, and atherosclerosis 2, 3, 4
- Skull base tumors, including metastatic neoplasms 2
- Microvascular ischemia, which is a frequent cause of acute isolated cranial nerve six (CN VI) palsy 3
- Central nervous system (CNS) mass lesions, which are the most common cause of sixth nerve palsy in young adults 5
- Multiple sclerosis, which is the most common cause of isolated sixth nerve palsy in young adults 5
- Elevated intracranial pressure (nontumor) 6
- Trauma 6
- Congenital conditions 6
- Inflammatory conditions 6
- Idiopathic causes, where no underlying cause can be found 6
Specific Age Groups
In children, the most common cause of sixth nerve palsy is neoplasms or their neurosurgical removal, followed by elevated intracranial pressure (nontumor), traumatic, congenital, inflammatory, and miscellaneous causes 6. In young adults (20-50 years old), the most common cause of sixth nerve palsy is a CNS mass lesion, although the most common cause for an isolated sixth nerve palsy in this age group is multiple sclerosis 5.
Risk Factors
Diabetes mellitus is a significant risk factor for sixth nerve palsy, with a 6-fold increase in odds of having diabetes in cases of sixth nerve palsy over controls 4. Systemic hypertension does not seem to be associated with increased odds of sixth nerve palsy, although coexistent diabetes and hypertension are more common in cases of sixth nerve palsy over controls 4.