Transcutaneous electrical nerve stimulation
A transcutaneous electrical nerve stimulation is a device that produces mild electric current to stimulate the nerves for therapeutic purposes. TENS, by definition, covers the complete range of transcutaneously applied currents used for nerve excitation, but the term is often used with a more restrictive intent, namely, to describe the kind of pulses produced by portable stimulators used to reduce pain. The unit is usually connected to the skin using two or more electrodes which are typically conductive gel pads. A typical battery-operated TENS unit is able to modulate pulse width, frequency, and intensity. Generally, TENS is applied at high frequency with an intensity below motor contraction or low frequency with an intensity that produces motor contraction. More recently, many TENS units use a mixed frequency mode which alleviates tolerance to repeated use. Intensity of stimulation should be strong but comfortable with greater intensities, regardless of frequency, producing the greatest analgesia. While the use of TENS has proved effective in clinical studies, there is controversy over which conditions the device should be used to treat.
Medical uses
Pain
Transcutaneous electrical nerve stimulation is a commonly used treatment approach to alleviate acute and chronic pain by reducing the sensitization of dorsal horn neurons, elevating levels of gamma-aminobutyric acid and glycine, and inhibiting glial activation. Many systematic reviews and meta-analyses assessing clinical trials looking at the efficacy of TENS for different sources of pain, however, have been inconclusive due to a lack of high-quality and unbiased evidence. Potential benefits of TENS treatment include its safety profile, relative affordability, ease of self-administration, and availability over-the-counter without a prescription. In principle, an adequate intensity of stimulation is necessary to achieve pain relief with TENS. An analysis of treatment fidelity—meaning that the delivery of TENS in a trial was in accordance with current clinical advice, such as using "a strong but comfortable sensation" and suitable, frequent treatment durations—showed that higher-fidelity trials tended to have a positive outcome.Acute pain
For people with recent-onset pain i.e., fewer than three months, such as pain associated with surgery, trauma, and medical procedures, TENS may be better than placebo in some cases. The evidence of benefit is very weak, though.Musculoskeletal and neck/back pain
There is some evidence to support a benefit of using TENS in chronic musculoskeletal pain. Results from a task force on neck pain in 2008 found no clinically significant benefit of TENS for the treatment of neck pain when compared to placebo. A 2010 review did not find evidence to support the use of TENS for chronic low back pain.Another study examining knee osteoarthritis patients found that TENS demonstrated efficacy and a better safety profile relative to weak opiates. Given the age, comorbidity frequency, tendency toward polypharmacy, and sensitivity to adverse reactions among individuals most frequently reporting osteoarthritis, TENS could be a non-pharmacological alternative to analgesics in the management of knee osteoarthritis pain.
Neuropathy and phantom limb pain
There is tentative evidence that TENS may be useful for painful diabetic neuropathy. As of 2015, the efficacy of TENS for phantom limb pain is unknown; no randomized controlled trials have been performed.A few studies have shown objective evidence that TENS may modulate or suppress pain signals in the brain. One used evoked cortical potentials to show that electric stimulation of peripheral A-beta sensory fibers reliably suppressed A-delta fiber nociceptive processing. Two other studies used functional magnetic resonance imaging : one showed that high-frequency TENS produced a decrease in pain-related cortical activations in patients with carpal tunnel syndrome, while the other showed that low-frequency TENS decreased shoulder impingement pain and modulated pain-induced activation in the brain.
Labor and menstrual pain
Early studies found that TENS "has been shown not to be effective in postoperative and labour pain." These studies also had questionable ability to truly blind the patients. However, more recent studies have shown that TENS was "effective for relieving labour pain, and they are well considered by pregnant participants." One study also showed that there was a significant change in laboring individuals' time to request analgesia such as an epidural. The group with the TENS waited five additional hours relative to those without TENS. Both groups were satisfied with the pain relief that they had from their choices. No maternal, infant, or labor problems were noted. There is tentative evidence that TENS may be helpful for treating pain from dysmenorrhoea, however further research is required.Cancer pain
Non-pharmacological treatment options for people experiencing pain caused by cancer are much needed, however, it is not clear from the weak studies that have been published if TENS is an effective approach.Bladder function
and transcutaneous electrical nerve stimulation in the tibial nerve have been used in the treatment of overactive bladder and urinary retention. Sometimes it is also done in the sacrum. Systematic review studies have shown limited evidence on the effectiveness, and more quality research is needed. A major trial found that in a care home context transcutaneous posterior tibial nerve stimulation did not improve urinary incontinence.Dentistry
TENS has been extensively used in non-odontogenic orofacial pain relief. In addition, TENS and ultra low frequency-TENS are commonly employed in diagnosis and treatment of temporomandibular joint dysfunction. Further clinical studies are required to determine its efficacy.Tremor
A wearable neuromodulation device that delivers electrical stimulation to nerves in the wrist is now available by prescription. Worn around the wrist, it acts as a non-invasive treatment for those living with essential tremor. The stimulator has electrodes that are placed circumferentially around a patient's wrist. Positioning the electrodes on generally opposing sides of the target nerve can result in improved stimulation of the nerve. In clinical trials reductions in hand tremors were reported following noninvasive median and radial nerve stimulation.Transcutaneous afferent patterned stimulation is a tremor-customized therapy, based on the patient's measured tremor frequency, and is delivered transcutaneously to the median and radial nerves of a patient's wrist. The patient specific TAPS stimulation is determined through a calibration process performed by the accelerometer and microprocessor on the device.
The Cala ONE delivers TAPS in a wrist-worn device that is calibrated to treat tremor symptoms. Cala ONE received de novo FDA clearance in April 2018 for the transient relief of hand tremors in adults with essential tremor and is currently marketed as Cala Trio.
Contraindications
People who have implanted electronic medical devices including pacemakers and cardiodefibrillators are not suggested to use TENS. In addition, caution should be taken before using TENS in those who are pregnant, have epilepsy, have an active malignancy, have deep vein thrombosis, have skin that is damaged, or are frail. The use of TENS is likely to be less effective on areas of numb skin or decreased sensation due to nerve damage. It may also cause skin irritation due to the inability to feel currents until they are too high. There is an unknown level of risk when placing electrodes over an infection, but cross contamination with the electrodes themselves is of greater concern.There are several anatomical locations where TENS electrodes are contraindicated:
- Over the eyes due to the risk of increasing intraocular pressure
- Transcerebrally
- On the front of the neck due to the risk of an acute hypotension or even a laryngospasm
- Through the chest using anterior and posterior electrode positions, or other transthoracic applications understood as "across a thoracic diameter"; this does not preclude coplanar applications
- Internally, except for specific applications of dental, vaginal, and anal stimulation that employ specialized TENS units
- On broken skin areas or wounds, although it can be placed around wounds
- Over a tumor or malignancy, based on in vitro experiments where electricity promotes cell growth
- Directly over the spinal column
Cardiac pacemakers