Electrostimulation for the Management of Pain: TENS and IFC

What is pain?

“An unpleasant sensory and emotional experience associated with actual or potential tissue damage, ordescribed in terms of such damage.”

International Association for the Study of Pain

What influences pain perception?

Culture

Motivation

Emotion

Past experience

Purpose of pain

Protective sensation

• Encourages withdrawl

• Protects damaged area during healing

Indicator of pathology or injury

Acute Pain

• Lasting <12 weeks

• Well located and defined

• Results from injury or disease that causes tissue damage

• Infection, trauma, metabolic disorder

• Serves to protect against further injury

Chronic Pain

• Persistent or recurrent

• 3-6 months or beyond expected healing time

• Structural and functional changes in CNS

• Associated with central sensitization

• No longer protective

Referred Pain

Occurs at site removed from site of injury or disease

Thought to be due to convergence of cutaneous, visceral, and skeletal muscle nociceptors on a common nerve root in the spinal cord

Theories of Pain ControlGate Control Theory

• “Large diameter afferent stimulation activates local inhibitory circuits in the dorsal horn of the spinal cord and prevents nociceptive impulses carried by small diameter fibers from reaching the brain.”

  • Said another way: the spinal cord acts as a gate and determines if pain signals will reach the brain and lead to pain perception

• Opening/closing is influenced by

  • Stronger noxious stimuli (more activity in pain fibers)

  • Activity in other fibers (A beta can close the gait and inhibit pain perception. i.e.rubbing an area decreases pain)

  • Efferent pathways from brain

Gate control theory - Opening/closing is influenced by

• Stronger noxious stimuli (more activity in pain fibers)

• Activity in other fibers (A beta can close the gait and inhibit pain perception. i.e.rubbing an area decreases pain)

• Efferent pathways from brain

Gate Control Theory

• Stimulate large A-beta fibers to block A-delta or C fibers

• A-beta stimulate interneurons in substantia gelatinosa(in SC)

• Inhibits pre-synaptic transmission of A-delta and C

Additional Pain Theories

Endogenous Opioid Model

Biopsychosocialmodel

Why the Variety in Pt Response?

Gate control theory may explain “how”; sensitization may explain “when” it works

Peripheral sensitization-

• reduction in threshold and increased response at peripheral end of sensory nerve fiber

• Tissues are more sensitive

• Nociceptors have a lower threshold and fire more easily

• Occurs at the site of injury

Central sensitization

• Occurs at the brain and spinal cord

• Neurons become hyperexcitable and amplify the incoming signals

• Pain can persist after tissue healing and be triggered by non noxious stimuli (allodynia)

Peripheral senstiization

where: tissue/nociceptor level

primary issue: inflamed tissue → inc nociceptor sensitivity

pain pattern: local, proportional to movement/load

duration: often acute/resolves with healing

central sensitization

where: spinal cord and brain

primary issue: CNS amplication → inc. signal processing

pain pattern: widespread, disproportionate, persistent

duration: often chronic, persists, beyond healing

Type of Pain Can Impact Effectiveness of TENS and IFC

• TENS can reduce peripheral and central sensitization markers – can block pain or dampen sensitization processes

• Evidence is stronger for peripheral acute/local pain

  • Works best when pain is driven by tissue input

• More variable effects on central mechanisms- can influence central sensitization but less predictable

TENS - Transcutaneous electrical nerve stimulation

• Electrical impulses delivered to nerve fibers via surface skin electrodes

• Commonly used modality in clinic and home

• Technically can be any type of current that activates nerve fibers without skin disruption

• Clinically refers to e-stim for pain relief

• Activation of current to surface electrodes to activate peripheral nerves

• Typically for pain modulation

• Typically is sensory stimulation with or without small muscle twitches.

• Does not require tetany like NMES

TENS - contraindications

• Pacemaker

• Implantable device

• Pregnancy

• Seizures

• Over carotid

• Over damaged skin

• Over DVT

• Hemorrhage

• Malignant tumors

• Over eyes or reproductive organs

TENS - Precautions

• Undiagnosed pain

• Over active epiphysis

• Impaired sensation

• Impaired cognition

Indications for TENS

• Acute or chronic pain relief

  • Post surgical/incisional pain

  • Prior to painful technique

  • Phantom limb pain

  • MANY other painful conditions

• Used to overcome pain that prevents a pt from participating in therapeutic tasks

• Reduced reliance on pain meds

Good Evidence Support - TENS

• Chronic pain

  • TENS was more effective than placebo in managing chronic MSK pain (Lefebvre, 2020)

  • Short term pain relief and improved function

• Acute pain

  • Beneficial for reduced pain post surgery or injury (Cagnie, 2015)

• May be as effective as NSAID’s for pain relief in individuals with MSK pain (Zhong, 2017)