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Diabetic Neuropathy

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Diabetic Neuropathy

What is diabetic neuropathy ?

Diabetic neuropathy means damage of nerve fibers in people with diabetes. How the nerves are injured is not entirely clear but research suggests that high blood glucose changes the metabolism of nerve cells and causes reduced blood flow to the nerve. There are different types of nerves in the body. These can be grouped as :

  • sensory (detect sensation such as heat, cold, pain)
  • motor (contract muscles to control movement)
  • autonomic (regulate functions we cannot control directly, such as heart rate and digestion)

The most common type of diabetic neuropathy affects the nerves in the legs and is usually known as peripheral neuropathy. This is the type of neuropathy that causes foot problems. It affects mainly the sensory nerves although the motor and autonomic nerves can also be involved with important consequences.

What problems can be caused by diabetic neuropathy ?

Neuropathy can result in two sets of what superficially appear to be contradictory problems. Most patients who have neuropathy have one of these problems but some can be affected by both.

  1. loss of ability to feel pain and other sensation which leads to neuropathic ulceration.
  2. symptoms of pain, burning, pins and needles or numbness which lead to discomfort.

A typical neuropathic ulcer is shown in the figure below. Patients with neuropathy lose their sensation of pain. As a result, they exert a lot of pressure at one spot under the foot when they walk, building up a callus at that site without causing discomfort. The pressure becomes so high that eventually it causes breakdown of tissues and ulceration. The patient hardly notices any pain.

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A typical neuropathic ulcer is painless, surrounded by callus, associated with good foot pulses (because the circulation is normal), at the bottom of the foot and tips of toes

Are you at high risk of developing a neuropathic ulcer?

This will be dealt with more thoroughly in the section on Foot examination.

Briefly, you are at risk if :

  • you have had a foot ulcer before
  • you have lost a lot of sensation in the feet when your doctor tested it
  • you do not follow advice to protect your feet with good footwear and hygiene

Remember that even if you have no pain in the feet, it does not mean you are not at risk. On the other hand, just because you have pain in the feet does not necessarily mean you are facing ulceration and amputation.

What sort of treatment is required for a neuropathic ulcer ?

Remove the precipitating cause eg. replace shoes that are too tight. Remove the callus regularly to relieve pressure. This usually needs to be done every week. It is best carried out by a podiatrist accustomed to treating diabetic foot ulcers because experience is important to ensure adequate removal of callus. See image below which shows adequate removal of callus.

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Before Callus Removal

It is better for healing if the wound is kept moist under a foam dressing which protects the ulcer from further trauma and yet allows oxygen to get through. The old edict of keeping a wound dry and painting it with antiseptics is no longer thought to be the treatment of choice. Do not clean the ulcer with anything that is too caustic (eg strong Eusol or hydrogen peroxide) because this can damage the tissue further.
 

A good rule of thumb is not to put anything on the ulcer that you wouldn't put in your eye.

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A properly dressed wound

Taking antibiotics if the ulcer is infected. Remember, most foot ulcers are infected.
Many weeks of antibiotics may be required if the ulcer is not completely healed or if there is underlying osteomyelitis.

Rest the feet as much as possible because this helps to reduce pressure on the ulcer. Walking is not a good exercise for someone who has a neuropathic ulcer (or someone who is at great risk of developing one).

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Wearing an Orthowedge

If a neuropathic ulcer does not heal with the above conservative measures, more specialised methods of relieving the pressure may be needed. These may include wearing an Orthowedge designed to reduce pressure at the front of the foot where most of the neuropathic ulcers are situated.

Sometimes when all the above measures have been tried but the ulcer still does not heal, it may be necessary to ask a surgeon to correct some foot deformities which are causing too much pressure. Examples of this include removal of a clawed toe or a prominent metatarsal head

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Deformed toes which are causing excessive pressure at the tip and at the top.

Although blood supply is normal in a purely neuropathic ulcer, in real life many ulcers are neuro-ischaemic. In other words, there is a combination of impaired nerve function and poor blood supply. Therefore it would also be wise to check that blood supply is normal. Sometimes a neuropathic ulcer will only heal when blood supply is improved.

 
 

Painful Diabetic Neuropathy

Neuropathy or nerve damage due to diabetes can present as insensate neuropathy (sensory loss) or painful neuropathy. The majority of people have the insensate type. However approximately 4-7% of patients with diabetes suffer chronic, often distressing symptoms of pain, pins and needles or numbness in their feet.

Why do people get painful neuropathy?

This question is yet to be fully answered and is the subject of ongoing research. People with poorly controlled diabetes for a long time are more likely to get chronic painful neuropathy. However, many patients with relatively well controlled diabetes also develop it.

Painful symptoms can be transient, eg. less than 12 months duration. These symptoms are often associated with periods of high blood glucose levels, or paradoxically, when the blood glucose level rapidly improves. In these acute situations, once the blood glucose has stabilised for a few months, the symptoms often spontaneously disappear.

Once symptoms have persisted for more than 12 months, they are less likely to disappear on their own. Although good blood glucose control is important for many reasons, striving for very tight blood glucose control is less likely to make the painful symptoms get better when they have been present for this length of time.

A number of theories have been suggested as to why chronic pain or symptoms develop. It is thought that:

  1. high blood glucose causes changes to the nerve fibres which results in abnormal nerve signals
  2. high blood glucose causes changes to blood vessels which supply the nerves
  3. unknown factors release chemicals that irritate the nerves and activate pain receptors

What type of symptoms do people get?

There is a wide variety of symptoms that people describe. More often the feet are affected, but the legs and sometimes hands can be involved as well.

Commonly reported symptoms include:

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Burning, feeling like the feet are on fire

 

People with painful neuropathy may also complain of:

  • Allodynia which means feeling pain from a stimulus that would not normally be painful. An example of this is wearing shoes or having bed sheets touching the feet
  • Hyperalgaesia which means having an exaggerated response to a stimulus which is normally painful. This is often seen in response to heat
  • a feeling of tightness or pressure around the feet
  • vibration or tingling sometimes described as ants crawling under the skin

Does the pain increase my risk of serious foot problems or amputation?

Not necessarily. If you have normal sensation and good circulation, having pain on its own will not increase your risk of foot problems. This is important, as often just knowing this will help to ease the distress. However, if you also have sensory loss or poor circulation in addition to pain, your risk of foot problems is increased and you need to take proper care of your feet. See section on Foot Care for People with High Risk Feet.

How is it Treated?

Firstly it is important to determine if the pain is due to diabetes or some other cause. People with pain should have a thorough assessment.

Pain due to diabetes is usually:

  • present in both feet
  • of equal severity in each
  • often, but not always, worse at night

If the pain is in one foot only, it is likely from another cause such as arthritis, spinal problems, other neuropathies or peripheral vascular disease, which should be investigated by the appropriate medical personnel.

If diabetes is determined to be the cause, and is sufficiently distressing to warrant treatment, there are a number of options available. Unfortunately, neuropathic pain is not easy to treat and not all treatments are helpful for all people. It is important to understand that for some people, several treatments may need to be tried or used in combination to achieve acceptable symptom relief.

Some commonly used treatments include:

Acupuncture

This is particularly suitable for people who do not like taking tablets.

It is thought to work by suppressing painful signals from reaching the brain. More commonly these days, the treatment involves passing a small electric current through the needles.

Cream containing Capsaicin

Capsaicin is an ingredient found in chilli peppers. It is particularly helpful for people who experience burning pain. It reduces pain by removing a chemical called substance P from the nerves which is needed to transmit certain pain signals. To achieve symptom relief, a strength of 0.075% or greater should be used which is found in a number of preparations. The cream is applied topically to the feet, so is also good for people who do not like taking tablets. However, it needs to be applied several times per day, so the person needs to be motivated to apply it regularly, and able to reach their feet easily or have someone available to do it for them.

It is important to note that capsaicin may cause burning or discomfort when first applied. Treatment should persist for at least a month to determine its effectiveness.

Tricyclic Antidepressants

These agents are the tried and tested treatment for neuropathic pain. They are helpful in many cases but their use is often limited by side effects such as urine retention, dry mouth and daytime drowsiness, although some newer preparations are less likely to have these effects. They are usually taken at night, which helps to improve sleep. They should be used in caution with people with glaucoma or the elderly.

Antidepressants in other classes may also be proven to be successful, but at the moment there are few scientific studies to support their use.

Anticonvulsants

Have been shown to be helpful in some people. One agent Gabapentin, has proven to be promising but at this stage is only allowed for treating epilepsy. A drug related to Gabapentin is currently undergoing clinical trials. If successful, it will be marketed for use in treating painful neuropathy.

Anti-arrhythmic Agents

These drugs, primarily used for regulating heartbeat or local anaesthesia, are sometimes helpful in treating painful neuropathy. They work by blocking the electrical conduction of painful signals along nerve fibres. The main agent used is Mexiletine. Its use is contraindicated in people who have an arrhythmia, so an ECG should be performed prior to use if there is any doubt. It is generally well tolerated but side effects include dizziness and nausea. Sometimes people are given a test with lignocaine, another drug in this class, to determine if Mexiletine will be helpful in their situation.

Analgesics

For minor pain, simple analgesics, such as paracetamol or aspirin are often helpful. However, until now, it has been generally accepted that opiates or narcotic agents are not helpful in relieving neuropathic pain. A newer non-narcotic agent known has Tramadol, has been shown in a few small trials to have promising results.

Psychological considerations

Chronic pain is not just a product of physical abnormalities. Psychological factors have significant influence over how an individual perceives and deals with pain. As such, psychological support is integral to the treatment of chronic pain. Formal assessment and counseling should be made available to people who have difficulties in coping with their pain.

 

 

 

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Last modified: 01/21/16