Sixth cranial nerve palsy has many causes, including damage to small blood vessels by diabetes, but the cause is often unidentified.
The affected eye cannot turn fully outward and may turn inward when people look straight ahead.
Doctors can identify 6th cranial nerve palsy based on the symptoms, but tests, including brain imaging, are done to try to identify the cause.
Sixth cranial nerve palsy usually resolves whether the cause is identified or not.
(See also Overview of the Cranial Nerves Overview of the Cranial Nerves Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk. Some of the cranial nerves are involved in the special senses (such as seeing... read more .)
Palsy refers to paralysis, which can range from partial to complete.
Many disorders can cause this palsy:
Tumors
A bulge ( aneurysm Aneurysms of Arteries in the Arms, Legs, and Heart An aneurysm is a bulge (dilation) in the wall of an artery. (See also Aortic Branch Aneurysms and Brain Aneurysms.) Aneurysms may occur in any artery. Aneurysms are most common in the aorta... read more ) in an artery in the skull
Brain infections Overview of Brain Infections Infections of the brain can be caused by viruses, bacteria, fungi, or, occasionally, protozoa or parasites. Another group of brain disorders, called spongiform encephalopathies, are caused by... read more , such as meningitis, a brain abscess, or a chronic fungal infection
Complications of an ear or eye infection
Blockage of an artery supplying the nerve, as can result from diabetes, a stroke Ischemic Stroke An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more
, a transient ischemic attack Transient Ischemic Attacks (TIAs) A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply. The cause and symptoms... read more , or vasculitis Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more 
(inflammation of blood vessels)Idiopathic intracranial hypertension Idiopathic Intracranial Hypertension Idiopathic intracranial hypertension is characterized by increased pressure within the skull (intracranial pressure). What triggers the disorder is unknown. People have daily or near daily headaches... read more (pseudotumor cerebri)
Sometimes high blood pressure
Rarely, upper respiratory infections (in children)
Some of these disorders, such as tumors and brain abscesses, increase pressure within the skull and put pressure on (compress) the nerve. Other disorders, such as a blocked artery, interfere with blood flow to the nerve.
If 6th cranial nerve palsy occurs alone (without other cranial nerve palsies), its cause is often never identified.
Symptoms of Sixth Cranial Nerve Palsy
The affected eye cannot turn fully outward and may turn inward when people look straight ahead. Double vision occurs when people look toward the side of the affected eye.
Other symptoms in people with 6th cranial nerve palsy depend on the cause. For example, disorders that increase pressure inside the skull may cause a severe headache and temporary blurring of vision when people move their head suddenly. Also, the face and mouth may be numb, and people may be unable to move the affected eye in other directions.
Diagnosis of Sixth Cranial Nerve Palsy
Neurologic examination
Eye examination, including ophthalmoscopy
Computed tomography or magnetic resonance imaging
Sometimes a spinal tap
Sometimes blood tests
Usually, doctors can easily identify a 6th cranial nerve palsy, based on results of a neurologic examination Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the nervous system. Examination of the nervous system—the... read more and an eye examination, including ophthalmoscopy. However, the cause is usually less obvious.
An ophthalmoscope What Is an Ophthalmoscope? 
is used to look into the eye and check for evidence of increased pressure within the skull and abnormalities in blood vessels.
Computed tomography (CT) or, preferably, magnetic resonance imaging (MRI) of the brain is done to exclude tumors and other abnormalities that may be increasing pressure within the skull. If results of imaging are normal, a spinal tap Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Electroencephalography (EEG) is a simple, painless procedure in which... read more 
(lumbar puncture) may be done to determine whether an infection or bleeding is present.
If symptoms suggest vasculitis, blood is withdrawn to check for evidence of inflammation, such as certain abnormal antibodies (antinuclear antibodies and rheumatoid factor) and an abnormal erythrocyte sedimentation rate (ESR—how quickly red blood cells settle to the bottom of a test tube containing blood).
Doctors may do blood tests to check for diabetes Screening for diabetes Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , especially if people have risk factors for it, such as older age, high blood pressure, a family history of diabetes, or obesity. Doctors may measure fasting blood glucose levels Blood glucose measurement Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more and hemoglobin A1C level Hemoglobin A1C Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more or do an oral glucose tolerance test Oral glucose tolerance test Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more .
After all tests are done, the cause may remain unknown.
Treatment of Sixth Cranial Nerve Palsy
Treatment of the cause
Treatment of 6th cranial nerve palsy depends on the cause. When the cause is treated, the palsy usually resolves.
Palsies with no identifiable cause usually resolve without treatment within 2 months, as do those due to a blocked blood vessel.
