Neuropathy is one of the three most common complications suffered by people with diabetes (along with retinopathy and kidney disease). As its name implies, neuropathy affects the nervous system.
There are two major types of neuropathy: one affects the autonomic nervous system and the other targets the sympathetic nervous system.
The autonomic nervous system is like an electric generator. It controls the automatic functions (those unconscious bodily functions) like breathing and circulating the blood. Autonomic neuropathy leads to such problems as gastroparesis (delayed digestion), incontinence, cardiovascular irregularity, and sexual disfunction in both men and women. Impotence is the most common manifestation of autonomic neuropathy, affecting more than half of all men with diabetes.
The sensory nervous system is responsible for sensation and can be likened to household electrical wiring since it loops through the entire body. Sensory neuropathy may cause numbness and tingling in the extremities, slowed reflexes, and episodes of pain. The nerves of the fingers and toes are affected most often.Tingling and numbness may be worse at night and does not tend to fluctuate in response to changing blood sugar levels.
The Varieties of Neuropathy
Peripheral (in the hands and feet), symmetric (affecting both sides of the body) and poly (involving several nerves) neuropathy are typical forms of diabetic neuropathy. Other types include mononeuropathy, cranial neuropathy, proximal neuropathy, and entrapment neuropathy.
Mononeuropathies affect only one nerve. Cranial neuropathy affects the cranial nerves and is prevalent in older people with type 2 diabetes. It may occur suddenly without any of the other symptoms of neuropathy. The primary mononeuropathy occurs in the third cranial nerve, causing a sudden blinding headache behind the eyes, and drooping of the eyelids. The pain usually subsides within two to three months, but may recur again.
Compression mononeuropathy is the result of damage to a single nerve which becomes compressed due to anatomical structure or restricted blood flow. Carpal tunnel syndrome, which affects the hands and fingers, is the most typical form of compression neuropathy.
Taking Care of the Pain
Pain management for neuropathy is a complex issue. Many treatments are available, but the elimination of discomfort due to neuropathy has remained elusive.
In a study conducted by the Diabetes Research and Treatment Center at Southern Illinois University and School of Medicine, and the Diabetes Center of Excellence at Humana Hospital in Lexington, Kentucky, three distinct types of neuropathic pain were identified: superficial pain, characterized by burning and tingling; deeper pain experienced as “pins and needles;” and muscle pain, characterized by cramping, aching, and muscle tenderness (Diabetes Care, August 1993).
Large nerve fibers in the body carry impulses for voluntary actions or muscle reaction, while small nerve fibers carry impulses for pain. These allow us to sense hot and cold, according to Dr. Rup Tanden, associate professor in the department of neurology at the University of Vermont College of Medicine.
Most neuropathies involve damage to both large and small nerve fibers, resulting in numbness and loss of sensory detection. In cases where only small nerve fibers are damaged, however, the regeneration of those nerves causes hyper-excitability. These abnormally excitable regenerating nerve fibers correspond to the superficial pain described above.
Anyone who had frostbitten ears will understand this phenomenon; as ears with frostbite begin to warm up, the intensity of pain increases. In such cases, physicians often wait before prescribing pain killers since the discomfort often spontaneously disappears on its own.
However, it is important to distinguish between the disappearance of pain and numbness. The presumed spontaneous disappearance of neuropathic pain may actually be the result of a damaged nerve, which transmits pain while it is dying but ceases to transmit pain once it is completely dead.
As Aaron Vinik, MD, PhD, professor at the Diabetes Research Institute at Eastern Virginia Medical School writes: “The disappearance of pain may reflect improvement of nerve function or, alternately, indicate that neural function has deteriorated to the extent that it is no longer sufficient to transmit pain.” In other words, the end of nerve pain does not necessarily indicate the healing of neuropathy, but may instead indicate the transition to a more serious, though less painful, condition.
One of the primary dangers of numbness due to advanced peripheral sensory neuropathy is the increased risk of undetected trauma to the area of numbness. The feet are especially at risk, since they are prone to injuries and diabetic ulcers. For this reason, proper attention and care of the feet is extremely important for people with neuropathy in order to reduce or prevent the incidence of gangrene and amputation. It is benificial to test the feet regularly for loss of sensation.
In the study described above (Diabetes Care, August 1993), each of the three types of pain were treated differently, based on the understanding of its cause. Superficial pain, attributed to the hyper-excitability of regenerating nerve fibers was treated with capsaicin (Zostrix-a topical cream). Deep electric pain, which is thought to result from some form of nerve cell body or nerve root dysfunction, was treated systematically, using a combination of imipramine, an antidepressant, and mexiletine, a heartbeat regulator. And muscle pain, thought to be caused by a feedback loop (in which nerve stimuli creates a muscle spasm, which causes more nerve stimuli, which creates more muscle spasm, and so forth), was treated with a combination of stretching exercises and metaxalone, a muscle relaxant.
The results of the study demonstrated dramatic pain improvement for all three categories of pain, suggesting that proper diagnosis is a key to successful treatment.
The Earlier, the Better
Early detection is of critical importance. It has been found that if impotence due to autonomic neuropathy is treated early (before nerve fibers have deteriorated to the point where there is no function at all),there is a chance that the damaged nerves can regenerate, and the impotence can be reversed by treatments such as direct drug injections (intracavernosal therapy).
However, if the neuropathy remains untreated for six months or more, there is little hope of reversal. A study conducted by the American Diabetes Association examining the relationship of diabetic neuropathy to glycemic control over a five-year period has shown that normalization of blood glucose levels in newly-diagnosed patients prevents deterioration of nerve conduction. Improvement in later stages of the disease does not return nerve function to normal levels, but may prevent future damage and alieve symptoms (Clinical Diabetes, March-April 1993).
Causes of Neuropathy
Dr. Aaron Vinik describes neuropathy as a complex disease with multiple causes including: metabolic dysfunction, involving both hyperglycemia and essential fatty acid deficiency; autoimmune response involving antibodies discovered in the nerve tissue of people with diabetes which actually destroys the nerve tissue itself; and hypoxia (a lack of sufficient oxygen leading to nerve damage). (Diabetes Review 3:139-157, 1995).
In a study of 48 patients, Zvi Ram and associates found a connection between poor blood circulation due to vascular disease and peripheral neuropathy (Archives of Neurology, December, 1991). However, Dr. Vinik suggests that while hypoxia is clearly involved in mononeuropathies and is prevalent among older people with type 2 diabetes, its role in polyneuropathies is unclear. It is not known whether hypoxia causes nerve damage in polyneuropathies, or is instead the result of already deteriorating nerves which cause blood supply to diminish.
Vinik argues that both genetic and environmental causes, such as tobacco and alcohol use, play a more primary role than hypoxia in the development of neuropathy. Newer studies also implicate autoimmune self-destruct mechanisms in nerve damage for certain people.
Constant Care is Best
Neuropathy is a multi-faceted condition and treatment requires a clear understanding of the specific type of nerve damage involved.
In addition, studies linking high blood sugar levels to neuropathic and circulatory problems clearly suggest that the best treatment for neuropathy is prevention by normalization of blood sugar levels. Research on a variety of nutritional supplements suggests that supplements may facilitate the normalization of blood sugar levels. In particular, magnesium, vitamin B, vitamin E, and gamma linoleic acid have all shown positive results, as have the reduction or elimination of alcohol and tobacco use.
Other forms of treatment, such as the use of antidepressants (imipramine, amitriptyline) and anti-convulsants, are helpful in pain management but unpleasant side effects may outweigh benefits. Massage and stretching exercises can also help.
Regardless, due to the prevalence of numbness and related foot trauma, proper attention and care of the feet is important for anyone with neuropathy.
The most effective kinds of treatment are those aimed toward the specific type of neuropathy involved and those which address the causes of the neuropathy, rather than its symptoms.