From the Guidelines
Transcutaneous Electrical Nerve Stimulation (TENS) treats chronic pain by delivering low-voltage electrical currents through electrodes placed on the skin near the painful area, working through the gate control theory and triggering the release of endorphins, as supported by a higher-quality Cochrane review 1.
Mechanism of Action
The mechanism of TENS in treating chronic pain involves two primary ways:
- Stimulating nerve fibers that block pain signals from reaching the brain (gate control theory)
- Triggering the release of endorphins, the body's natural painkillers A typical TENS treatment involves placing adhesive electrodes on clean, dry skin around the painful area and adjusting the device to deliver electrical pulses at comfortable intensity levels.
Treatment Sessions
Treatment sessions usually last 20-30 minutes and can be repeated several times daily as needed.
- Most TENS units allow adjustment of pulse frequency, with high-frequency settings (80-120 Hz) working best for acute pain and low-frequency settings (2-10 Hz) often more effective for chronic conditions.
- Proper electrode placement is crucial for effectiveness, and the device should never be placed over broken skin, near the eyes, across the chest, or during pregnancy without medical supervision.
Effectiveness
TENS effectiveness varies among individuals, with some experiencing significant relief while others notice minimal benefits, as noted in a systematic review of acupuncture for low back pain that found no difference in short- or long-term pain relief between TENS and acupuncture in 4 trials 1. Some key points to consider:
- A higher-quality trial found TENS superior to superficial massage 1
- Evidence from single, lower-quality trials is insufficient to accurately judge efficacy of TENS versus other interventions for chronic low back pain or for acute low back pain 1
- The Cochrane review found that one third of patients randomly assigned to either active or sham TENS had minor skin irritation, with 1 patient (in the sham group) discontinuing therapy because of severe dermatitis 1
From the Research
Mechanism of Transcutaneous Electrical Nerve Stimulation (TENS) in Treating Chronic Pain
- The exact mechanism of TENS pain relief is unknown, but it is believed that TENS impulses interrupt nociceptive signals at the dorsal horn of the spinal cord 2.
- TENS may modulate pain processing at the level of the dorsal horn, in brainstem centers mediating descending inhibition, and within the pain matrix 3.
- Remote analgesic effects of conventional TENS may occur through modulation of pain processing at the level of the dorsal horn, in brainstem centers mediating descending inhibition, and within the pain matrix 3.
- TENS can activate the descending pain-inhibitory pathway, leading to pain reduction 2.
- Periaqueductal gray (PAG) and lateral prefrontal cortex functional connectivity is increased by TENS, and modulated by testosterone and cortisol 2.
Types of Analgesia
- Three types of remote analgesia have been identified:
- at the contralateral homologous site
- at sites distant from stimulation but innervated by overlapping spinal segments
- at unrelated extrasegmental sites 3
Clinical Evidence
- Over 30 studies have reported remote analgesic effects of conventional TENS, including studies using animal models of pain, experimental pain in humans, and clinical studies in subjects with chronic pain 3.
- TENS has been shown to be effective in reducing pain intensity in some studies, but the evidence is generally considered to be of very low quality due to methodological limitations and small sample sizes 4, 5, 6.