Peripheral nerve damage

The central nervous system controls everything that we do and every thought that we have but these central nerves are encased in the skull and spine.

To get nerve signals between the central nervous system and the rest of the body, long nerve cells named peripheral nerves extend into the more distant tissues.

This peripheral nervous system consists of nerves that take signals to the fingers, toes, legs, hands and abdomen, and then carry information back to the central nervous system.

Peripheral nerves convey many types of messages to and from the central nervous system:

• Sensory nerves allow us to feel sensations, some transmit the sensation of touch, some conduct pain signals and others carry messages about temperature
• Motor nerves carry messages from the brain to the muscles to initiate movement. These nerves can also be called somatic nerves
• Autonomic nerves carry messages to tissues and organs such as the heart and hormone producing glands to control heart rate and release of key hormones such as adrenalin

The peripheral nerves carry messages in the form of electrical impulses. So, in structure, peripheral nerves are like wires: they have a central core through which electrical impulses run and are surrounded by insulation to help in conduction.

In peripheral nerves this insulation is called myelin.

Peripheral nerves carry all of the information to and from the central nervous system, so if they are damaged, this can lead to many conditions – in fact, more than 100.

Peripheral nerve damage usually affects either motor or sensory nerves but rarely both types.

Peripheral nerve damage can occur at several locations:

Peripheral nerves that are some distance away from the central nervous system

This can stop the transmission of signals between the body and the brain. The damage can be due to nerves being cut in an accident, or because of other diseases that kill the nerve cells (this is called neuropathy).

Neuropathy can happen after a viral infection; it is common after shingles, or as a result of chronic diabetes. It can also be due to deficiency of some vitamins, such as vitamin B.

The myelin sheath in any peripheral nerve

This type of peripheral nerve damage can arise in some autoimmune conditions like Guillain–Barre syndrome or multiple sclerosis. The lack of the myelin sheath reduces the speed and efficiency of signal transmission along the peripheral nerve.

Peripheral nerves as they exit the spine

This is often due to a herniated vertebral disc, an accident, or a cancerous tumour, that presses on the nerves. It can result in a blockage of nerve transmission, with loss of movement and/or sensation, and often causes extreme pain.

Peripheral motor nerves where they meet muscles.

This can be caused by syndromes like myasthenia gravis and stops the muscles working, causing mobility problems and paralysis.

Specific disorders and peripheral nerve damage

Peripheral nerve damage is involved in several specific disorders:

Pinched nerves or trapped nerves

That develop after an injury or accident can cause peripheral neuropathy, which can lead to severe neuropathic pain.

Restless leg syndrome

Where nerve damage in the lower limbs causes an irresistible urge to move the legs, particularly when in bed at night.

Sciatica

Usually felt as severe shooting pains down one side of the body, is due to peripheral nerve damage at the point where the nerve exits the spine.

Diabetic neuropathy

In which chronically high levels of blood sugar in diabetics leads to widespread peripheral nerve damage. This usually causes pain and a loss of sensation in the limbs and is also accompanied by blood vessel damage, which can lead to foot ulcers and leg ulcers that are slow to heal.

Damage to specific motor peripheral nerves

This can cause paralysis and neuropathy in sensory nerves can lead to numbness, stopping you feeling sensations like touch or pain.

Autonomic peripheral nerve damage

This can interfere with hormone production; this can cause poor function of the pituitary gland, leading to acromegaly, or to the hypothalamus, causing Cushing’s syndrome or to the thyroid gland, causing hyperthyroidism or hypothyroidism.

As you might expect, the symptoms of peripheral nerve damage vary greatly. However, they can be generally divided into:

• Feeling numb in a specific area of the body
• Pain that can range from mild through to severe and debilitating
• Getting a burning or tingling sensation, like pins and needles, but worse
• Feeling as though your muscles have become very weak
• Being over-sensitive to touch to the extent that even a light touch can cause pain

With such a range of disorders affecting the peripheral nerves, getting a firm diagnosis of exactly what the problem is can take time.

As well as doing a thorough examination and talking in detail about your different symptoms, your GP or neurologist may also recommend some tests.

These can include nerve conduction studies, CT scans, and MRI scans to discover the full extent of the peripheral nerve damage that you have.

Do peripheral nerves regenerate?

Generally, nerve cells do not regenerate well but peripheral nerves can repair themselves, depending on where they are damaged.

This means that you can expect a full recovery if you develop some types of peripheral nerve damage.

In other cases, the damage cannot be repaired and symptoms are instead controlled using medication and lifestyle changes.