Transcutaneous Electrical Nerve Stimulation: Too Experimental for PHN?

Transcutaneous electrical nerve stimulation, also known as TENS or TNS, involves placing tiny electrodes over the region experiencing pain. The electrodes deliver electrical impulses to nearby nerve pathways, relieving the pain (Mayo Clinic). Unfortunately, the process is very experimental: it does not work for everyone, and in fact can exacerbate the pain. The exact reason for relief is not known, although it is believed that the new electrical impulses trigger the release of endorphins, a natural painkiller.

On their website, Aetna lists the following as medically necessary for postherpetic neuraglgia (PHN): tricyclic antidepressants, gabapentin, pregabalin, opioids (oral), antivirals (oral), lidocaine patch, and intrathecal corticosteroids. However, it decrees TENS "experimental and investigational because their effectiveness for this indication has not been established" (Aetna clinical policy bulletin number 0725). According to the same site, there have been findings that report positive effects of TENS on some patients with PHN, but no validated, randomized and controlled study has been conducted. Additionally, in 1995 Reeve and Corabian evaluated evidence for clinical success of TENS on acute and chronic pain and found the results inconclusive.

Overall, TENS offers an interesting alternative to many PHN treatments; however, it raises the question, why use a treatment with significantly less conclusive results when you can use a less-questionable treatment? Admittedly, one positive reason to try TENS is its few side effects: it's not invasive, addictive, can be used for indeterminate amounts of time, and does not interfere with oral medications. It should not, however, be used with patients who have pacemakers because the electrical signals of the two devices could interfere with one another. The side effects that have been experienced with TENS include skin irritation from the electrode pads, and burns from extended exposure to stimulation. Yet, even with minor side effects, TENS has not proved to be any more revolutionary or helpful than other established treatments. Also, on a personal note, although I recognize that there are still many things about the body's processes that we do not understand, and this lack of comprehension does not prevent them from being effective, I would nevertheless favor a treatment that works through a known mechanism (particularly if it yields the same results).

But on the other hand, simply because we have not developed the treatment or the studies to their fullest extent does not mean we should dismiss it; there can be ample room for improvement. in an effort to give equal consideration to both sides of the TENS debate, it should be noted that although the treatment may be cumbersome and experimental, it nevertheless requires little effort from the patient and could be very manageable for people who do not need to travel much. And, of course, it would be very worthwhile if it eliminated PHN pain.

TENS can also be used to administer topical steroid medication through the skin to treat acute pain, because the electrical current it generates helps move the steroids into soft tissue, reducing inflammation. The TENS unit is battery-operated portable; it can be worn around the waist and can be turned on or off as needed for pain control. They can cost anywhere from approximately one hundred dollars, all the way up to six hundred dollars from the top manufacturers. The units are purchased or rented with a prescription, and a physical therapist should be consulted on the proper placement of the electrodes. Generally, TENS is used on a trial basis before being recommended as a long-term treatment. Of course, before using a TENS unit, be sure you have spoken to a physical therapist or doctor and know how to work the device and set the electrical signals at appropriate levels.

Lidocaine Patches and PHN

Postherpetic neuralgia is a complication of shingles, which occurs when the virus that causes chicken pox remains in the body, dormant in nerve cells. Shingles manifests as rash and blisters accompanied by pain, but sometimes the pain remains even after the skin condition has disappeared. This is postherpetic neuralgia. Although there are a number of treatments, including steroids, painkillers, and even antidepressants, lidocaine skin patches offer one easy-to-use alternative with (usually) no side effects.

In a 1999 blind study conducted by the Education and Research in Pain Medicine and Palliative Care (Beth Israel Medical Centre, New York), researchers found that 78% of the subjects preferred the lidocaine patch treatment over that of a placebo. Simply put, lidocaine patches are small patches (much like band-aids) that contain lidocaine, which can be applied directly to the skin to numb the areas experiencing pain.

Dermaflex and Lidoderm are two leading providers of lidocaine patches, with Dermaflex offering 2% lidocaine patches and Lidoderm offering 5%. Although PHN can be treated as effectively with pills (taken orally), which are absorbed internally, the patch has the positive feature of not requiring an increase in dosage. Another positive aspect of the patch is that it requires less attention: a patient can wear up to three patches at a time, for twelve hours without interruption (followed by twelve hours without the patch). Additionally, because the patch is not absorbed internally but through the skin, it carries an even smaller risk of interacting negatively with other medications. Side effects are minimal and rare; they include: Mild redness, swelling, burning, blisters, bruising, irritation, change in skin color, or numbness at the application site. Risk of cardiac arrest is increased for those on antiarrhythmic medications. Of course, if you experience any effects more serious than these (confusion, dizziness, allergic reaction), consult your doctor immediately.

On the other hand, the negative aspect of the treatment is that the patch needs to cover the skin where there is pain. If the region of pain is larger than the patch, it can still be effective (assuming size difference is not extreme and the lidocaine is applied to the most painful region), but the patch cannot be worn on the face, and many patients find it inconvenient to use the patch if the affected skin is not under clothing.

Lidocaine works by blocking sodium channels in the neuron (nerve cell) cell membrane. These sodium channels are responsible for nerve signal movement among nerve cells, and when blocked, the sodium cannot move in and out of the cell to amplify the sensory signals as they travel through the body. Thus, the action potential of the nerves is decreased and the lidocaine produces anaesthetic effects. The lidocaine patch, because it focuses the area being treated, can selectively treat postherpetic neuralgia.