Diabetic peripheral neuropathic pain (DPNP) affects an estimated 10% to 20% of the more than 20 million people in the United States who have diabetes mellitus.1,2 The pain can be severe and can markedly interfere with functioning. Although there is no cure for DPNP, for many patients the pain can be controlled to a degree sufficient to improve their quality of life.
Here I outline a variety of effective management strategies, including topical agents, oral medications, and nonpharmacological therapies (eg, acupuncture and transcutaneous nerve stimulation).
ETIOLOGY
As with most types of neuropathic pain, the cause of DPNP is unknown. Although DPNP appears to be related to pathological changes in the peripheral nerves, why pain develops in some patients with demonstrable peripheral neuropathy but not in others remains unclear. This disparity has resulted in more attention being paid to the role of the brain and the rest of the CNS in the development and perpetuation of pain.3
Improved glucose control seems to reduce the overall risk of diabetic peripheral neuropathy, but whether good control specifically decreases the incidence of DPNP has yet to be determined.4
DIAGNOSIS
Symptoms. Patients usually describe DPNP as a burning or electric shock sensation, usually in the feet and lower limbs, although the hands may be affected as well.5 Patients may also experience allodynia, in which ordinarily nonpainful stimuli induce pain, or hyperalgesia. Even when patients are experiencing pain, they may also feel numbness over the affected area.
Although patients with lower extremity pain usually report that placing weight on their feet exacerbates the pain, DPNP frequently worsens at night. This can cause or exacerbate sleep disorders. Insomnia has been associated with abnormal glucose tolerance test results and may precipitate diabetes mellitus.6
Evaluation. DPNP is the most likely diagnosis in a patient with diabetes mellitus who has foot or lower limb pain. A 2-hour oral glucose tolerance test is recommended for patients who have this type of pain but who have not yet been evaluated for diabetes mellitus.7 However, there are other potential causes of peripheral pain that should be considered, including pain related to vitamin B12 deficiency, claudication, and osteoarthritis. These causes can usually be differentiated from DPNP by appropriate testing.8
In patients with DPNP, neurological studies (such as nerve conduction velocity and quantitative sensory tests) usually demonstrate a reduction peripheral nerve function. However, there is minimal correlation between the results of these tests and the presence or severity of DPNP; thus, they provide limited assistance in making the diagnosis. These tests should not routinely be ordered for patients who are believed to have DPNP.
TREATMENT
There are now several published guidelines on neuropathic pain in general and more specifically on DPNP.5,9-11 These guidelines provide extensive references to support their recommendations. For the most part, the guidelines are in agreement about which therapies appear to be most effective. Treatment recommendations based on these guidelines are provided in the Table. Note that only 2 medications have an FDA-approved indication for the treatment of DPNP: pregabalin(Drug information on pregabalin) and duloxetine(Drug information on duloxetine).
Topical analgesics. If the pain is relatively localized, I recommend beginning treatment with the lidocaine(Drug information on lidocaine) patch 5%. Although it has an FDA-approved indication only for the treatment of postherpetic neuralgia, the patch is also effective for DPNP.12 Furthermore, as I explain to patients, the patch has a localized action and therefore is very unlikely to cause systemic adverse effects or to interact with other medications. This is a significant advantage for many persons with diabetes, who often have comorbid conditions.
The lidocaine patch is recommended for localized pain because only up to 3 patches can be applied at a time. The patches are worn for 12 hours and then removed. Since the analgesia continues for 12 hours after they are removed, it usually does not matter when they are applied; for ease of use, most patients put them on in the evening and then remove them the next morning.
The patch also provides a physical barrier between the outside environment and the painful area. This is an added benefit for patients with DPNP who have allodynia or hyperalgesia, in which external stimuli may exacerbate the pain. However, it is important to caution patients that the lidocaine patch should be placed only over intact skin; therefore, the patches should not be applied to the painful ulcers that many patients with diabetes experience.
The other topical analgesic that is commonly used for DPNP is capsaicin. Before the lidocaine patch 5% was introduced, I frequently prescribed this medication, but I have found the lidocaine patch to be more effective. Also, many patients with DPNP are unable to tolerate the sensation of heat that occurs at the site where capsaicin (which is made from chili peppers) is applied, especially if allodynia is present.13
