AUTHOR: Marc Mitnick DPM
REVIEWED BY: Podiatric Medical Review Board
home --> neuropathy
abnormal neurological sensations in the feet and legs
WHAT IS PERIPHERAL NEUROPATHY
Peripheral neuropathy also known as peripheral nerve disease is one of the most common diseases no one has ever heard of. An estimated 15-20 million Americans suffer from some form of neuropathic disorder.
It is caused by the deterioration of the nerves that lead to the ends of the limbs (hands and feet). This makes it impossible for the body and spinal column to communicate with the muscles, bone and other tissue that makes up the upper and lower extremity.
The peripheral nervous system is the body’s “electrical wiring system". Any disruption in this system will cause foot pain symptoms such as burning, tingling, numbness, itchiness, and occasional shooting pains all the way to unremitting pain. Peripheral neuropathy will also lead to an abnormal gait and eventual breakdown of the feet due to the inability of the body to “feel" the ground that you are walking on. If left untreated peripheral neuropathy can lead to permanent loss of nerve function, tissue damage and muscle atrophy.
Causes of peripheral neuropathy include: disease, nerve compression, nerve entrapment, laceration of a nerve through trauma or surgery, exposure to toxins, and inflammation. In many cases, especially in people over the age of 60, no cause can be determined and this is known as idiopathic neuropathy.
Early intervention is very important in treating neuropathy. Identifying the source of the neuropathy and rectifying the problem, if possible, will go a long way to eliminating the worst cases of neuropathy. Many sources of neuropathy are not treatable, but symptomatic relief of the neuropathy can be achieved.
Medication induced neuropathy, although rare is one type of neuropathy where once the offending medication is removed, the symptoms of neuropathy will subside. This is also true of toxic induced neuropathy, where exposure to a toxic agent is causing the peripheral neuropathy.
Some of the more common medications known to cause neuropathy include: statin drugs, colchicine, allopurinol, Taxol (a chemotherapeutic agent for ovarian and breast cancer), Amiodarone (an anti-arrhythmic drug), some antibiotics and even thalidomide which has come back into vogue for treatment of HIV related ulcers.
Neuropathy can be a consequence of dose regulation of the various drugs, in certain cases considered a minor side effect in an effort to fight a more potent disease, eg: cancer.
Other causes of neuropathy include:
- metabolic disorders
- autoimmune disorder
- chronic kidney failure
- rheumatoid arthritis
- infectious disease such as lyme disease
- vitamin deficiencies
- liver failure
The two most common forms of neuropathy that I see are diabetic neuropathy (See my discussion on diabetic neuropathy in the foot) and radiculopathy, which is a neuropathy that originates from the nerve roots as they come out of the spinal column. Pressure on the nerve from any number of sources as the nerve comes out of the spinal column can cause an adverse neurological event in the feet.
In instances where there has been trauma such as in a car accident or a fall the diagnosis is somewhat easier to make; it becomes much more difficult in the older individual where the radiculopathy is the result of degenerative arthritis of the spine. The picture can be further clouded when symptoms of neuropathy are actually the result of poor circulation as seen in older individuals.
Finding an exact cause of neuropathy can be very difficult, if not impossible, in many cases. Tools that are available in trying to isolate the cause include the following:
proper medical history- the two most important questions your doctor should be asking are your symptoms and location of your neuropathy.
Symptoms include: numbness, tingling, sharp shooting pain, burning pain, gait imbalance, muscle weakness, intolerance to heat, dry skin and feet that do not perspire, as well as skin atrophy.
Location would include both feet equally experiencing the same symptoms, or is it limited to one foot. Additionally, the area of the foot/feet that is involved. Are the symptoms spreading?
If the symptoms are occurring equally in both feet, a systemic cause should be investigated. If only one foot is involved then investigation should be geared toward conditions such as radiculopathy, trauma and nerve entrapments.
lab work- blood tests can be helpful in identifying or eliminating possible causes. A HemoglobinA1c reflects a person's average blood sugar over a period of three months. If this is elevated, diabetes has to be ruled out as a source.
A complete blood count, CBC, should be performed to rule out anemia as the culprit.
Nutritional testing may be considered to rule out Vitamin B and Vitamin D deficiencies.
Testing for elevated levels of heavy metals (lead, mercury, copper, zinc, chromium) as well as Lyme titer can be useful.
diagnostic testing- The standard tests over the years has been nerve conduction studies which essentially looks for a "break" in the conduction capacity of a nerve. These tests are especially helpful if the doctor suspects a nerve entrapment. This test offers little help in diagnosing neuropathy associated with systemic causes.
Epidermal nerve fiber density test ENFD is a relatively new test used to measure systemic causes of neuropathy. A small biopsy of skin is taken at the level of the outer foot and a second biopsy approximately 10 centimeters above the outside portion the ankle. Under a microscope, the amount of small nerve fibers are actually counted and compared against a standard. Most people with systemic sources of neuropathy will show a decrease in the number of nerve fibers. After therapy begins, the test is repeated to see if there is a quantitative improvement in the neuropathy.
TREATMENT FOR NEUROPATHY IN FEET
Treatment is geared to finding the cause of the neuropathy. As stated earlier many causes of neuropathy cannot be remedied so treatment becomes symptomatic.
Treatment options for reducing pain include:
physical therapy- this is usually reserved for neuropathy involving one limb as a result of nerve compression or nerve entrapment
injection therapy- in the foot, at least, injection of steroids is indicated for local entrapment of nerves.
surgical intervention (tarsal tunnel, decompression spinal surgery)- Along the lines of decompression surgery (where the tissue surrounding the affected nerve is removed to take pressure off the nerve) there is a school of thought that neuropathy that is often diagnosed as diabetic neuropathy may actually be compression neuropathy. It has been theorized that peripheral nerves in diabetics "swell" more than non-diabetics and that the swelling of these nerves puts excessive pressure on the nerves as they pass thru tight spaces in the leg and foot. Such would be the case with tarsal tunnel where the tibial nerve, once swollen, is trapped on the inside of the foot below the ankle resulting in neuropathic symptoms.
Further proof of this theory would be the fact that the tarsal tunnel counterpart in the wrist known as carpal tunnel is much more prevalent in diabetics.
The idea here is for your doctor to rule out tarsal tunnel and other lower extremity nerve entrapments first before making a diagnosis of diabetic neuropathy and going forward with oral medication.
oral medication- Cymbalta is an FDA approved medication for neuropathy. Side effects include constipation, diarrhea, headaches, dry mouth , nausea and dizziness. Neurontin, although not FDA approved is an off label use for neuropathy. Side effects include low blood pressure, dizziness, drowsiness and fatigue. Lyrica is another oral medication usually best served in diabetic neuropathy.
Metanx, a prescription medication is a combination of folate and vitamin B components which has been shown to be effective in treating diabetic neuropathy.
Recent research has suggested that some nutritional supplements may help reduce neuropathic pain.
Specifically acetyl l-carnitine, 600mg. per day has demonstrated the ability to reduce neuropathic symptoms in some individuals. This supplement will probably have to be taken for a couple of months before any relief is noticed.
In the November, 2006 issue of "Diabetes Care" reference is made to the benefits of alpha-lipoic acid in oral doses for the reduction of diabetic neuropathy. Various doses were tested but it was found that a once daily dose of 600 mg. was enough to see relief in as little as two weeks. The nutritional supplement was effective in reducing the stabbing and burning symptoms of neuropathy but had little effect on numbness. In clinical practice I have found a minimum dose of 1200mg per day is necessary in reducing symptoms of peripheral neuropathy. Once again it is important to point out that if you are going to try nutritional supplements make sure you purchase quality supplements as this industry is not completely regulated by the FDA and therefore many vitamins on the market are of poor quality.
"Whether the observed favorable short-term effect of ALA on neuropathic symptoms and deficits can be translated into slowing the progression of diabetic polyneuropathy in the long term is unknown," the authors write. (Dr. Dan Ziegler from Heinrich Heine University, Duesseldorf, Germany and colleagues) "However, our finding that neuropathic deficits such as impaired sensory function were improved is encouraging, because these are major risk factors in the development of neuropathic foot ulcers."
topical medication-lidocaine patches applied locally may also relieve the symptoms of neuropathy. Side effects include lightheadedness, dizziness and drowsiness.
A topical preparation called capsaicin, known commercially as Zostrix neuropathy cream, has been used with some degree of success. Made from a pepper derivative, when applied topically to the affected area a few times a day, over the course of a few weeks many patients begin to feel a reduction in their symptoms.
Other topical prescription preparations have become popular in recent years. Compounding pharmacies have put together compounds containing the same medication that is usually taken orally. This makes for a safer, but possibly less effective, way to try various medications. Most compounding pharmacies have their own formulas and in many cases they can be modified by orders from your doctor. Topical medication has less chance of having systemic side effects.
combined electrochemical treatment- this relatively new treatment modality combines electrostimulation with nerve blocks performed on the nerves running into the feet. Both methods are not new treatments, but only recently have clinicians started performing them together.
The combination of the two treatments reduces pain signals into the feet, increases blood flow to the feet and reduces inflammation to the nerves. The treatment is done over a period of 8-16 weeks and many patients have reported relief long after the treatments have ended.
The companies offering the electrostimulation units advertise upwards of an 80 percent success rate, but these results have been performed on small samplings. Larger studies are needed to confirm these initial findings.
BIG TOE NUMBNESS
One of the more common neuropathies I see in the office is the patient's complaint that their big toe is numb, either in one toe or both great toes.
Initially, my first thought is either that of a local irritation of the nerves that affect the big toes such as may occur after wearing a certain pair of shoes, or after doing a certain activity that perhaps the patient does not do on a regular basis.
My second consideration is that of a radiculopathy which is an irritation of a specific nerve that comes out of the spinal column. The cause of a radiculopathy can be from a number of factors, most of which, are mechanical in nature.
I mention this because many people will present with big toe numbness and immediately think they have diabetes. While I suppose diabetic neuropathy might cause those symptoms, most neuropathy related to diabetes is more broad based in the feet and constant regardless of what the patient is doing.
Additionally diabetic neuropathy will be present regardless of the activity of the patient, while big toe numbness from other sources will either be better or worse depending on what the patient is doing at any given moment, such as lying in bed vs. hiking (as an example).
Many people have written in to me with this complaint, click here to read about their experiences with big toe numb
National Institutes of Health
Want more information? CLICK HERE