Transcutaneous Electrical Nerve Stimulation

Introduction

• TENS is a noninvasive, peripheral stimulation technique to relieve pain. During TENS, pulsed low voltage electrical currents are delivered using electrode pads attached to the skin surface to stimulate the underlying nerves.¹
• TENS is a nonpharmacological technique for pain relief. As a result, there is no direct potential for abuse, although there may be benefits when used as an adjunct with pharmacotherapy.²
• Patients are able to self-administer TENS as needed, with the ability to adjust the pulse amplitude to alter the analgesic effect.¹
• Intensity of TENS is a critical factor in efficacy. Applications of TENS at inadequate intensities has been shown as one of the primary factors attributing to conflicting reports of TENS efficacy.²

TENS Device

• The TENS device consists of a battery-powered, hand-held device with electrode pads that attach to the skin surface. The user can adjust the current’s amplitude, frequency, duration, and pattern to achieve the desired effect.¹
• There are three different TENS techniques: conventional TENS, acupuncture-like TENS, and intense TENS.

Mechanism of Action

Conventional TENS

• Conventional TENS utilizes low-intensity (paresthesia, not painful), short-duration (pulse width of 50-200μs), and high-frequency (50-100 Hz) current.¹
• The conventional method elicits segmental analgesia by stimulating large diameter, nonnoxious, A-beta nerve fibers.¹
  • A-beta fibers activate interneurons within the dorsal horn of the spinal cord, specifically the substantia gelatinosa. These activated interneurons inhibit the second order neurons of the spinothalamic pathway. As a result, the painful stimuli is not transmitted to the primary somatosensory cortex (gate control theory of pain).³
• There is a reduction in nociceptor activity at a segmental/dermatologic level for a localized analgesic effect.³
• Conventional TENS is the least intense of the three techniques. As a result, the conventional method is the most common. Patients typically start with the conventional method and then move on to the acupuncture-like or intense method if adequate pain control is not achieved.

Acupuncture-like TENS (AL-TENS)

• AL-TENS uses high-intensity (to tolerance threshold), longer-duration (pulse width of 100-400μs), and low-frequency (2-4 Hz) current to produce strong but comfortable muscle twitches.¹
• AL-TENS stimulates A-delta nerve fibers.¹
  • The A-delta fibers activate the descending pain modulatory system of the brain. The periaqueductal gray within the midbrain becomes activated by input from the cortex; neurons from the periaqueductal gray descend to the rostral ventral medulla. Neurons from the rostral ventral medial medulla descend to stimulate neurons within the substantia gelatinosa of the spinal cord. The neurons from the descending pain modulatory system will activate interneurons within the substantia gelatinosa, as well as inhibit the A-delta fibers.^2,3
• This technique leads to a diffuse analgesic effect. AL-TENS is used when the conventional method does not provide adequate pain relief.

Intense TENS

• Intense TENS also stimulates A-delta nerve fibers. Its analgesic effect also arises from its ability to activate the descending pain modulatory system.
• Intense TENS utilizes both high-intensity and high-frequency currents.¹
• It is the most intense of the three TENS methods.

Usage

• The patient should initially be started on conventional TENS with a continuous pulse pattern and mid-range frequencies (80-100 Hz) and duration (100-200μs).¹
• The settings can be adjusted as needed by the patient. Finding the settings that provide the best analgesic effect is done by trial and error.
• The electrodes should be placed on healthy sensate skin near the painful area.
• There is rapid onset and offset of pain relief with the use of TENS.

Clinical Indications

• TENS has been shown to be useful in the management of acute and chronic pain of nociceptive, neuropathic, and musculoskeletal origin.¹
• There are divided opinions for the use of TENS in alleviating acute pain.²
  • In cases of severe to moderate pain, TENS may be useful in combination with pharmacotherapy.
  • Negative outcomes have been reported in postoperative pain and labor pain management.
  • TENS may be beneficial for acute orofacial pain, painful dental procedures, fractured ribs, and acute lower back pain.
• Clinical experience supports the use of TENS for chronic pain management.¹ Randomized control trials have suggested benefits in cases of
  • localized muscle pain;
  • postherpetic neuralgia;
  • trigeminal neuralgia;
  • phantom limb and stump pain;
  • diabetic neuropathies and entrapment neuropathies;
  • radiculopathies (cervical, thoracic, and lumbar);
  • complex regional pain syndromes type I (reflex sympathetic dystrophy) and type II (causalgia);
  • cancer-related pain;
  • fibromyalgia; and
  • spinal cord-related injury, etc.

Adverse Effects and Contraindications

• Common adverse effects of TENS include contact dermatitis and skin irritation. Nausea and syncope have also been reported. Serious adverse effects from TENS are rare.¹
• The electrodes should not be placed over skin with dermatitis or eczema. The electrodes should also not be placed on the anterior neck near the carotid sinus, over the eyes, through the chest (anterior and posterior positions) or internally.¹
• TENS is contraindicated in patients with a pacemaker or any other form of implanted electrical devices.¹
• Pregnancy and epilepsy are other contraindications for the use of TENS.¹