Diabetic neuropathies are a family of nerve disorders that are a long-term complication of diabetes. The highest rates of neuropathy are found in people who have poor glucose control and have had the disease for more than 25 years.1 Cigarette smoking, alcohol consumption, age, height, and high cholesterol levels also are independent risk factors for neuropathy.2
Diabetic neuropathy affects sensory, autonomic, and motor neurons. Every organ system in the body is vulnerable to damage. The lower extremities are most commonly affected. The heart, gastrointestinal tract, and genitourinary system are commonly affected as well, however.
Most health care providers can easily recognize diabetic peripheral neuropathy, which is characterized by symptoms ranging from slight changes in sensation to the excruciating pain associated with focal neuropathy. The disease develops slowly and begins with a painless loss or change of sensation. The pattern of neuropathy begins in fingers and toes and progresses to a "glove and stocking" distribution.3 Patients may complain of burning, tingling, aching, numbness, sharp pain, or cold sensation. These painful symptoms occur in a minority of patients (11%-32%).4 The majority of patients experience a progressive lack of ability to feel pain or judge temperature. These problems can lead to limb amputation because of nonhealing foot ulcers.
Focal neuropathy appears suddenly and affects specific nerves, usually in the head, torso, or leg. It is very painful and unpredictable. Yet, it usually improves by itself over a period of weeks or months and does not cause long-term damage.
Treatment of neuropathy is notoriously difficult. There are 3 facets to treatment of diabetic neuropathy: primary prevention, symptom management, and disease modification. Prevention of the disease is critical. Prevention can be accomplished with optimal control of blood sugar and management of modifiable risk factors such as smoking, weight, and hypertension. The Diabetes Control and Complications Trial and the UK Prospective Diabetes Study demonstrated a marked reduction in neuropathic complications with tight glucose control.5,6
Treatments designed to control symptoms often turn into polypharmacy nightmares and are only moderately effective. These medication regimens may include tricyclic antidepressants; tramadol; anticonvulsives such as gabapentin, carbamazepine, and lamotrigine; selective serotonin reuptake inhibitors; bupropion; venlafaxine; and various narcotics. All of these agents have the potential for significant side effects and drug interactions.
Topical agents such as capsaicin cream and isosorbide dinitrate (ISDN) spray have been shown to be useful in pain management, although capsaicin cream must be used frequently and causes a burning sensation that may be intolerable in people who are already in pain. ISDN spray is not available in the United States.
OTC treatments such as NSAIDs have demonstrated efficacy in patients who rated their pain as "moderate." These drugs must be used carefully, however, due to the possibility of renal impairment in a population that is already at high risk for this complication. They are not generally used as monotherapy for diabetic neuropathy.
Complementary and alternative therapies also have been studied for peripheral neuropathy, with varying degrees of success. Electrostimulation, used transcutaneously or percutaneously, has had positive results in clinical trials. Yet, the trials had very strict exclusion criteria, which prohibited a large segment of the diabetic population from participating.7
Thioctic acid (also known as alpha-lipoic acid) has been shown to be useful for short-term relief of neuropathy. It requires daily 30-minute intravenous infusions, however which may limit its usefulness.1 Herbal manufacturers are promoting this compound in oral preparations, but these products are unlikely to be useful, given that the half-life of thioctic acid is 2 to 4 minutes.
Carnitine supplementation proved beneficial in 2 recent trials. Patients who took 1000 mg 3 times daily reported significant improvement in pain after 52 weeks of treatment. It took a minimum of 26 weeks, however, to notice any improvementwhich might lead patients to discontinue therapy prior to an adequate trial.8
Primary prevention is the most important part of diabetic neuropathy treatment. This aim can be achieved by optimal glucose control and modification of other risk factors.
Dr. Garrett is a clinical pharmacist practitioner at Cornerstone Health Care in High Point, NC.
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