Nerves power your entire body. But those nerves can be damaged by injury or an illness such as diabetes. Neuropathy is a disorder caused by nerve damage. It affects your ability to feel and move. Exactly how your body and your movement are affected depends on where in the body the damaged nerves are located. When nerves to or from the brain or brainstem are affected, it's called cranial neuropathy.

The cranial nerves are those that arise from your brain or brainstem. They often affect areas like the face and eyes. Some of the types of these neuropathies are:

• Bell palsy. This occurs when the facial nerve (seventh cranial nerve) is affected.
• Microvascular cranial nerve palsy. This affects one or more nerves, typically those that go to the eye. It is most common in people who have diabetes and high blood pressure.
• Third nerve palsy. This condition affects the third cranial nerve. This nerve helps manage muscles that control eye movement as well as the size of the pupil.
• Fourth nerve palsy. This is also called superior oblique palsy. It affects the superior oblique muscle, which helps you converge your eyes (to look at the tip of your nose).
• Sixth nerve palsy. This is also called cranial nerve VI or abducens palsy. It affects the sixth cranial nerve, which also helps control eye movement.

If several cranial nerves are affected, it is called multiple cranial neuropathies.

Cranial neuropathy can develop for many reasons. These include:

• Infections. Infections in the spinal fluid can irritate cranial nerves. For example, Lyme disease often affects the seventh nerve. But it can cause problems with any cranial nerve.
• Cancer. Cancer cells can spread to the spinal fluid and damage one or more cranial nerves. Sometimes cancer can press on cranial nerves as they run through the skull.
• Increased intracranial pressure from a tumor, head trauma, or brain swelling. This can injure cranial nerves. Pressure can also be raised in certain headaches. Cranial nerves 3, 4, and 6 are most often affected.
• Congenital cranial neuropathies. These are nerve injuries from trauma that occurs at birth. Or they can occur before birth from developmental problems or infection.
• Microvascular cranial nerve palsy. This can develop in people who have high blood pressure or other vascular risks, such as diabetes or smoking. Poor circulation to the cranial nerves injures them. It most often affects cranial nerves 3, 4, and 6.
• Autoimmune abnormalities. These occur when the immune system attacks one's own cranial nerves. This can happen in Guillain-Barré syndrome or lupus.
• Aneurysm. This can press on nearby nerves. It most often affects cranial nerves, 3, 4, and 6.
• Inflammatory diseases. These include sarcoidosis and multiple sclerosis.

Symptoms depend on which nerves are damaged and where they are located. Generally, neuropathies can cause:

• Pain.
• A tingling sensation.
• Numbness.
• Abnormal smell or taste.
• Skin that feels sensitive to the touch.
• Ringing in the ears or tinnitus.
• Weak or paralyzed muscles. This can cause drooling, choking, or slurred speech.
• Vision changes and double vision.

Some of the symptoms of cranial neuropathies include:

• Bell palsy can cause drooping of part of the face. It usually affects only one side of the face.
• Microvascular cranial nerve palsy can cause double vision, droopy eyelid, and other problems with eyesight.
• Third nerve palsy can cause an eyelid to sag and droop, double vision, trouble moving the eye, and a pupil that is bigger than normal.
• Fourth nerve palsy causes the eye or eyes to turn abnormally. It sometimes makes you see double. It may force you to tilt your head when looking.
• Sixth nerve palsy can cause abnormal movement of the eye and double vision.

A doctor will often do several tests to diagnose neuropathy. Depending on the type of neuropathy your doctor suspects, you may need:

• A nervous system exam to test sensation, reflexes, balance, and mental status.
• Blood tests to look for infections or health conditions, such as diabetes.
• Electromyography, which measures the electrical activity of muscles when working and at rest.
• CT or MRI scans, which are imaging tests of the brain.
• Nerve conduction velocity tests to help find out how and where the nerve is damaged.
• Biopsies of the skin and nerves to find out how severely nerves are damaged.
• Hearing tests.
• Spinal tap (lumbar puncture) to look for infection or inflammation in the spinal fluid.
• Angiography, which is a special X-ray that uses contrast dye and takes pictures of your heart and blood vessels.

A cranial neuropathy could be the sign of a life-threatening emergency. It should be assessed by a doctor right away. Many types of cranial neuropathies will get better with time, without any treatment. Sometimes medicines can be used to treat an infection, help reduce swelling in or near a nerve, or help if the neuropathy is causing pain. For some types and in some cases, surgery may help. Other times, the nerve damage can't be treated or fixed.

But it's important to diagnose and treat any health conditions that are causing the neuropathy. Treating common causes like high blood pressure, infections, and diabetes can help to treat the neuropathy. Eating nutritious foods, not smoking, and limiting alcohol can also help manage it.

Cranial neuropathy can't always be prevented. But controlling common causes can help to reduce the risk of having it. You can:

• Reduce your risk factors for diabetes, stroke, and head injury.
• Manage your diabetes well, if you have the disease.
• Lower your blood pressure, if needed.
• Follow a healthy lifestyle that includes not smoking, getting regular exercise, staying at a healthy weight, and eating a balanced diet.

Many cranial neuropathies are not dangerous. They may get better on their own with time. But they can be bothersome.

The best way to manage a cranial neuropathy is to manage possible causes. These include diabetes, high blood pressure, infections, and brain tumors. You should also prevent head injury.

If the symptoms do not go away on their own, your health care team might recommend physical therapy, occupational therapy, or other choices to help with them. Talk with your doctor about other possible choices, such as surgery, if the condition affects your quality of life.

If you have been diagnosed with a cranial neuropathy, talk with your doctors about when you might need to call them. They will likely advise you to call if your symptoms get worse or if you develop new symptoms, such as pain, numbness, weakness, or changes in vision.

• Cranial neuropathies are caused by damage to one or more cranial nerves. These are nerves that arise directly from the brain. They affect movement and feeling in the eyes and face.
• The causes of cranial neuropathies include poorly controlled diabetes or high blood pressure, head injuries, infections, strokes, and brain tumors.
• Common symptoms can include weakness or loss of sensation in part of the face, or changes in vision.
• Some cranial neuropathies go away on their own. But others might be permanent. Controlling diabetes and high blood pressure can sometimes help. If symptoms do not go away, medicines, surgery, or other treatments might be helpful.

Tips to help you get the most from a visit to your doctor:

• Know the reason for your visit and what you want to happen.
• Before your visit, write down questions you want answered.
• Bring someone with you to help you ask questions and remember what your doctor tells you.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.
• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.
• Ask if your condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if you do not take the medicine or have the test or procedure.
• If you have a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your doctor if you have questions, especially after office hours or on weekends.