Transcutaneous Electrical Nerve Stimulation

Transcutaneous electrical nerve stimulation (TENS) is a modality frequently seen within the physical therapy clinic, particularly in the outpatient setting. Clinically, it has been traditionally seen as a way to stimulate the sensory nerves (Prentice, 2011). The thought behind its pain relieving mechanism being that the mind will be subsequently tricked into paying attention to the electrical stimulus rather than the painful stimulus of the affected area (Prentice, 2011). The theory is deemed the gate control theory, and by way of maximally stimulating the sensory nerves, the painful afferent impulses being sent to the spinal cord level will be perceived as less or even not at all (Prentice, 2011).  TENS can also be modified to work via the descending mechanisms or endogenous opiate mechanisms of pain control (Prentice, 2011).

            Low back pain is a common ailment seen within the physical therapy clinic, and as such TENS is often used to treat the condition. Numerous studies have addressed the use of TENS for the treatment of low back pain. Both supporting and refuting evidence has come from these studies. First we will take a look at a few of the current research surrounding TENS as a successful modality in the treatment of low back pain.

            In a study by Melzack, Vetere and Finch, the researchers wanted to address the effectiveness of two common treatments for low back pain: transcutaneous electrical nerve stimulation versus gentle massage over the affected area. The thought behind comparing the two treatments being that both methods provide stimulation to the area, so one sensory input should prove greater than the other. This was a double-blind, randomized study design, in which 41 patients participated. The McGill Pain Questionnaire was used to assess pain levels both before and after treatment. Additionally, the researchers assessed return to function and the affect of the modalities via a straight leg raises and ROM in the low back (specifically flexion). It was found that TENS significantly reduced pain relative to gentle massage(Melzack, Vetere, & Finch, 1983).

Additionally, straight leg raises were improved but no increase in ROM was seen with either modality. This suggests that healing was not stimulated but perhaps the use of TENS to decrease pain allows patients to complete tasks they were previously capable of but unable to do due to pain. Within the group receiving TENS, 85% showed improved pain scores, while only 38% showed improved pain within the gentle massage group. The researchers conclude that TENS is a superior method to pain treatment for low back patients.  One problem seen within this study is that one may question the “massage” employed within the treatment. The researchers applied 4 suction cups that administered specific pressure changes to the area. One could see this as more of a placebo to TENS rather than massage. Either way, TENS would be deemed better than massage or a placebo with the outcomes aforementioned (Melzack et al., 1983).

Another study supports the use of TENS in patients with nonspecific chronic low pain back for controlling pain intensity. Chronic low back pain was described as a duration of greater than three months. One hundred fifty patients were included in a single-blind randomized control trial and divided into three groups (50-50-50) for each TENS, Interferential Current (IFC), and controls.  Significant reductions in pain intensity were found in both the TENS and IFC groups such that 84% of the TENS group and 75% of the IFC group were able to stop using NSAIDs and analgesic drugs after treatment sessions compared with 34% of the control group (Facci, Nowotny, Tormem, & Trevisani 2011). However, most patients in each group were not using any drugs, so more investigation could be performed to solidify these results.

What was more of interest regarding the treatment of pain for subjects was the implied cumulative effect of pain relief over the treatment sessions. Patients were given ten treatment sessions over two weeks. Using a visual analog scale (VAS), patients were evaluated for pain both before and after each treatment session.  In both the TENS and IFC groups, patients had significant reduction in mean pain intensity at the beginning and end of each session and from over the course of treatments. In the IFC group, subjects had the greatest duration of pain relief after session nine and in the TENS group after session ten. It would be worth investigating what the maximal pain relief duration could be for the TENS group beyond session ten, however, only ten sessions were given in this study. The findings here imply that patients should see immediate reductions in pain intensity after each session as well as a cumulative effect of pain relief with more sessions. It is unknown the optimal number of sessions for maximal pain relief while utilizing TENS in treating chronic low back pain (Facci et al., 2011).

A study by Cheing and Hui-Chan examined if a single sixty minute treatment of TENS could modify chronic (clinical) LBP, acute (experimental) pain, and the flexion reflex, an objective pain measurement tool, versus a placebo. Multiple studies can be found that either refute or confirm the thought that placebo treatment is just as effective in modifying pain as TENS and other modalities. This study sought to compare the pain modification in experimental versus placebo group in just one sixty minute session of TENS.  Thirty subjects between the ages of 18 and 50 with chronic low back pain for more than 6 months and experiencing pain daily were included in the trial. Two visual analog scales were use for the subject to report their pain: the VAS (LBP) was used to indentify intensity of LBP and the VAS (FR) was used to record the electrical pain during the FR recording. Also, the flexion response was recorded electromyographically after elicitation by an electrical stimulus to the sole of the foot.

The results showed a decrease in pain to 63.1% using the VAS (LBP) value in the chronic LBP group, and there was no difference in the placebo group. This decrease in pain also remained for the next hour. There were no differences seen between group in the VAS (FR) and flexion response after treatment. These differences were also not seen in the acute experimental pain group. Therefore the researchers conclude that a single sixty minute treatment is indeed beneficial for reducing pain in patients with chronic low back pain as compared to placebo. They believe that this reduction in pain is not seen in patients with acute pain because different nociceptive pathways are used in modifying chronic versus acute pain (Cheing & Hui-Chan, 1999). 

From the above studies, we see that in some instances, TENS can be beneficial for patients with low back pain.  However, there is also current evidence that suggests otherwise. We will now review the studies that did not support the use of TENS for chronic low back pain.  

An evidenced based review by Dubinsky and Miyasaki shows that TENS is ineffective overall in the treatment of chronic low back pain. Two Class I studies were analyzed. In one scenario, TENS was compared to a TENS-sham group, and no benefit was found for TENS using a visual analog scales.  The TENS-sham group was given an apparent “treatment”, however no electrical current was delivered (Dubinsky & Miyasaki, 2010). This particular study was looking for a 20% significant improvement in pain, but this threshold was not reached.  Twenty percent is a liberal definition of significance in pain relief; some studies require 25% or even 50% to be considered significant. The authors of this review did not identify the specific percentage of relief attained (if any) in this scenario.  In the second study, TENS and TENS-sham were administered for patients with multiple sclerosis and chronic low back pain. There were no significant differences in pain relief. Thus, the authors concluded from both Class I studies that TENS is not a good treatment choice for chronic low-back pain (Dubinsky & Miyasaki, 2010). The authors did not indicate how many subjects were included in each study; that would have been helpful to determine the reliability of these studies.

In a different study by Chou and Huffman, researchers again wanted to explore the common modalities used within the physical therapy practice to treat low back pain. The researchers began by identifying common treatments including exercise, massage, diathermy, superficial head, transcutaneous electrical nerve stimulation and more. The authors then performed a review of literature surrounding the topic and included studies through 2006 (Melzack, Vetere & Finch’s study previously discussed in our article was included in this study).  They chose to only include randomized trials, which included outcomes for the treatment of low back pain. In summary, the study found that cognitive-behavioral therapy, exercise and spinal manipulation were moderately effective in chronic low back pain. In contrast, acute low back pain was only found to significantly improve via superficial heat and possibly spinal manipulation. Overall, through the review of 16 clinical trials specifically addressing low back pain and TENS, there is insufficient evidence to suggest TENS is superior to “sham TENS” or any other intervention. The systematic review also suggests that minor skin irritation occurs in 1/3 of patients receiving TENS (Chou & Huffman, 2007).

A study by Deyo et al, sought to determine if TENS was more effective than a general stretching and exercise program with sham TENS, and if the addition of TENS to an exercise program adds any benefit. One hundred forty- five patients were randomly assigned to 1 of 4 groups: TENs alone, TENS plus exercise, sham TENs alone, or sham TENS with exercise. The patients were assessed at follow ups on functional performance, pain (using VAS scales as well as self- rating intensity and frequency), and physical performance. The results found no additive benefit of TENS.  At a one month follow up there was no significant effect of TENS on functional performance, pain, or physical performance, and there was no additional effect seen when adding TENS to exercise. Also, there was no significant difference between the TENS and sham TENS treatments. The most significant result is that at the one month follow up, the exercise alone group showed decreased VAS scores, frequency of pain, and improved functional performance. However, it is important to note that at the two month follow up, if the subject in the exercise group had stopped doing their exercises, the before seen improvement were no longer there. Thus it is important to stress to patients that they need to continue their exercises if they want continued improvements in pain reduction (Deyo et al., 1990).

In analyzing the evidence both in support of and refuting the use of TENS for chronic low back pain; it is our opinion that TENS may have some pain relieving benefits for a certain patient group. The decrease in pain seems to be immediate, but not long too long in duration.  None of the studies reviewed claimed that the pain was nonexistent, but rather that the pain was decreased.  Whether you choose to use TENS or an alternative analgesic modality, we believe it is important to refer to current evidence and utilize best judgment for each patient situation.  

References

 
Cheing, G. & Hui-Chan, C. (1998). Transcutaneous electrical nerve stimulation: nonparallel           antinociceptive effects on chronic clinical pain and acute experimental pain. Archives of               Physical Medicine and Rehabilitation, 80(3), 305-312.

Chou, R., & Huffman, L. H. (2007). Nonpharmacologic Therapies for Acute and Chronic Low Back Pain: A Review of the Evidence for an American Pain Society/American College of Physicians Clinical Practice Guideline. Ann Intern Med, 147(7), 492-504. Retrieved from http://www.annals.org/cgi/content/abstract/147/7/492.

Deyo, R., Walsh, NE, Martin, DC, Schoenfeld, LS, & Ramamurthy, S. (1990). A Controlled Trial of Transcutaneous Electrical Nerve Stimulation (TENS) and Exercise for Chronic Low Back Pain. The New England Journal Of Medicine, 322: 1627–34.

Dubinsky, Richard M. & Miyasaki, Janis. (2010). Assessment: Efficacy of transcutaneous electric nerve stimulation in the treatment of pain in neurologic disorders (an evidence-based review): Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology 2010; 74;173.  doi: 10.1212/WNL.0b013e3181c918fc.

Facci, Ligia M., Nowotny, Jean P., Tormem, Fabio, & Trevisani, Virginia F.M. (2011). Effects of transcutaneous electrical nerve stimulation (TENS) and interferential currents (IFC) in patients with nonspecific chronic low back pain: randomized clinical trial. Sao Paulo Med Journal 129(4), 206-16.

Melzack, R., Vetere, P., & Finch, L. (1983). Transcutaneous electrical nerve stimulation for low back pain. A comparison of TENS and massage for pain and range of motion. Physical therapy, 63(4), 489-93. American Physical Therapy Association. Retrieved from http://ptjournal.apta.org/content/63/4/489.abstract

Prentice, William E. (2011). Therapeutic Modalities in Rehabilitation. (4^th ed.). China: McGraw-Hill Companies, Inc.