What are the causes of peripheral neuropathy?

Peripheral neuropathy is one of the prime causes of numbness in the toes and feet

What is neuropathy?

There are several different types and causes of peripheral neuropathy. Many of them lead to numbness, tingling and pain in the legs feet or toes. This can sometimes be confusing as these are also common symptoms of sciatica. The clue lies in the history and presentation which is different for this problem.

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Peripheral neuropathy is a global term for illness or injury to a peripheral nerve.

Peripheral nerves are the nerves that run from your spinal cord out into your limbs (as distinct from the central nervous system which is made up of your spinal cord and brain). The term explains itself if you break it down i.e. peripheral = edges, neuro= nerve, pathy= illness or pathology.

Peripheral nerves are made up of different type of nerve cells and fibres and they carry information to and from the brain via the spinal cord.

The three main types of fibre are:

• motor fibres that carry instructions about movement,
• autonomic fibres take care of the background business like sweating and hair growth
• sensory fibres that feedback information about feeling and touch

Signs and symptoms of peripheral neuropathy

Peripheral neuropathy can affect all these nerve fibres in different ways but the most common initial symptom is numbness and tingling or pain. This is because the sensory nerve fibres are affected and come to your notice first. The numbness and tingling often follows a pattern with this problem.

Numbness from an irritated sciatic nerve commonly follows the line of the nerve root called a dermatome. Peripheral neuropathy tends to be less defined or follows a sort of sock distribution. Imagine you have pulled on a pair of short socks. Sometimes the sock is just pulled on a little giving you a numb toe or toes, but sometimes the socks are pulled up more causing numb feet and legs all the way up to your knees.

Sock and glove distribution numbness seen with peripheral neuropathy - this is different to the lines of numbness seen with sciatica.

Sometimes the motor fibres are also affected leading to loss of power and control, like a drop foot for example.

What are the most common causes of peripheral neuropathy?

Anything that affects the nerve can lead to this type of problem. However it is helpful to split the causes of peripheral neuropathy into two broad categories

1. Diabetic neuropathy

2. Idiopathic and non-diabetic peripheral neuropathy

Diabetic Neuropathy Symptoms

This is one of the most common causes of peripheral neuropathy. It can affect all three different types of nerve in the limb and is caused by a variety of interlinked factors including metabolic, circulation and hormonal. Put very simply the nerves degenerate and they cannot repair themselves due to poor circulation as diabetes affects the blood supply.

Up to 20% of newly diagnosed diabetics will have these diabetic neuropathy symptoms rising to 50% in older diabetic people (Sherman 2009).

Non-diabetic and Idiopathic peripheral neuropathy

If the nerve is affected by trauma or entrapment anywhere along its length you can get symptoms of numbness and tingling. An example is meralgia paresthetica affecting the lateral cutaneous nerve in the thigh caused by entrapment at the groin.

There are a variety of other causes of peripheral neuropathy including alcoholism and vitamin B12 deficiency. Finally there is a large group of people where the cause of this problem is not clear. This is called idiopathic which means cause unknown.

Treatment for neuropathy

• First you need to make sure you have a correct diagnosis and not some other problem – go and see your doctor.
  
  
• Nerve conduction studies may be undertaken to determine the extent of the problem and get a proper diagnosis.
  
  
• Diabetic neuropathy is managed by tight blood sugar control with medication and lifestyle changes – see your doctor or diabetic nurse for advice.
  
• With other neuropathies finding the cause is the first goal, then controlling symptoms with medication and if needed using aids and supports that may help with weakness.

Don't confuse this condition with cervical myelopathy or lumbar spinal stenosis

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References and helpful web sites

Sherman, A.L., 2009. Diabetic Neuropathy: eMedicine Physical Medicine and Rehabilitation. Available at: http://emedicine.medscape.com/article/315434-overview

Patient.co.uk - good reliable patient centred information.

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Other Causes of Numbness

29-Jul-2017