Sixth Nerve Palsy: A rare disorder which causes weakness or paralysis of the nerves that supply sensation to your arms, legs, face and mouth. There are two types of sixth nerve palsy: sensory (S) and motor (M). Sensory type is caused by damage to the spinal cord while M type is due to damage to other parts of the body. The cause of both types may vary from person to person but most commonly it’s genetic.
Symptoms of sixth nerve palsy include numbness or weakness in one or both arms, leg(s), hands, feet and face. Affected individuals may have difficulty with fine movements such as writing, reading and even walking.
They may also experience pain when touched. Some affected individuals will not feel any symptoms at all and some people may develop severe symptoms within just a few days of being exposed to certain stimuli. Symptoms usually appear between the ages of five and 15 years.
Sixth nerve palsy is a very rare condition. According to the National Institute of Neurological Disorders and Stroke (NINDS), there were only nine cases reported in medical literature prior to 1980.
Since then, over 1,000 cases have been reported. Of those, only about 50% of them involved children under the age of fifteen years old. About 10% of these patients had no known family history of sixth nerve palsy.
Sixth nerve palsy affects both males and females of all races equally. Some studies have suggested that it may be slightly more common in males.
It has been found to be associated with several genetic disorders such as Down syndrome, Kallman Syndrome, Andermann Syndrome and Joubert Syndrome. Other genetic disorders without a prior history of nervous system abnormalities have also been reported to cause sixth nerve palsy.
In some cases, the cause is not known. The condition appears to occur randomly in people without any known risk factors.
For the reasons mentioned above, some researchers believe that some cases of sixth nerve palsy are in fact due to other conditions such as acute intermittent porphyria or arsenic poisoning.
The condition is named after the sixth cranial nerve which is also known as the abducens nerve. This nerve controls the lateral rectus muscle which is located in your eyeball and moves the eye outward.
It is the only muscle in the body that allows you to focus on a particular object and look at it directly. Since this nerve also carries sensory information from the eye to the brain, damage to it may cause double vision or a reduction in vision depending on where exactly the damage occurred.
Your body has 12 pairs of cranial nerves (CNs). These nerves begin in the brain and travel down the spinal cord to various parts of the body.
The names of these nerves are rather unimaginative: O for the olfactory nerve which controls smell, 1 through 7 for the optical nerves (which control vision), IX, X and XI for the spine, and CN III through CN XI for the auditory nerves (which control hearing). The remaining nerves are named using Arabic numerals. The abducens nerve is number 6.
The cause of sixth nerve palsy is the same as for most other types of paralysis. Either the upper motor neurons that control the movement (efferent signals) or the lower motor neurons that respond to the signals (afferent signals) can be damaged.
In the case of sixth nerve palsy, it’s believed to be damage to the lower motor neurons.
In most cases, the cause of sixth nerve palsy is unknown. The condition is most common in children under the age of 20 and some cases have been shown to be associated with infections such as HIV, measles, mumps, rubella, influenza and Coxsackie.
In most of these cases, the virus causes a swelling (inflammation) of the nerve which may be temporary or permanent.
In the majority of cases, there is no known cause. Some researchers believe that it may be due to a hereditary or genetic abnormality.
It has been linked to several genetic disorders such as Down Syndrome, Kallman Syndrome, Andermann Syndrome and Joubert Syndrome. Other diseases without nervous system abnormalities have also been linked to sixth nerve palsy specifically.
Most cases of sixth nerve palsy resolve on their own within three months with 50% recovering within the first month. Most cases in children are self-limiting and resolve themselves within three months.
In some cases a course of steroid medication may be prescribed to reduce the inflammation. If this doesn’t work, surgery may be necessary.
Surgery is normally only necessary if there is severe nerve damage such as an inability to move the eye. Even when surgery is done, the results are rarely completely effective and most people still have double vision after the operation.
In most cases, the double vision caused by the paralysis of the abducens nerve goes away on its own after three months. The loss of vision in the affected eye does not improve and may or may not be treated.
You should see an ophthalmologist (a medical doctor that specializes in the evaluation, treatment and surgery of disorders of the eyes) to confirm a diagnosis of sixth nerve palsy and rule out other possible causes. This is especially important since the symptoms are similar to a brain tumor or other serious disorders.
An ophthalmologist can provide additional and much needed medical help as well as a second opinion. The ophthalmologist may also be able to provide a prognosis on the chances of recovery of muscle control and whether or not there is any permanent damage.
At this time it is impossible to predict whether the paralysis will resolve itself or if it will remain permanently.
It is important to keep the head of the bed elevated when sleeping. This will decrease the fluid pressure in the eye and keep the fluid from building up any more than it already has.
If the paralysis is due to a brain tumor or other central nervous system cause, keeping this fluid out of the eye will prevent glaucoma from developing. Medication may also be required to decrease the pressure in the eye.
Surgical intervention is rarely necessary in this condition. It may be required in cases where there is an increased production of fluid in the eye or if surgery is required to correct other eye problems caused by the abducens nerve being paralyzed.
Even in cases of permanent paralysis, there is no loss of vision. The eye with the paralyzed muscle does not move and therefore has a fixed position.
The brain learns to turn off the vision in that eye so the person does not see double. In some cases the brain learns to ignore input from that eye (capture) and the vision is lost.
Sources & references used in this article:
Incidence, associations, and evaluation of sixth nerve palsy using a population-based method by SV Patel, S Mutyala, DA Leske, DO Hodge, JM Holmes – Ophthalmology, 2004 – Elsevier
Isolated sixth-nerve palsies in younger adults by ML Moster, PJ Savino, RC Sergott… – Archives of …, 1984 – jamanetwork.com
The natural history of acute traumatic sixth nerve palsy or paresis by JM Holmes, PJ Droste, RW Beck – Journal of American Association for …, 1998 – Elsevier
Bilateral sixth nerve palsy: analysis of 125 cases by JR Keane – Archives of neurology, 1976 – jamanetwork.com
Sixth nerve palsies in children by MS Lee, SL Galetta, NJ Volpe, GT Liu – Pediatric neurology, 1999 – Elsevier