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TENS Gate Control Mechanism — FRCA Final MCQ

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EasyPain MedicineTENS Gate Control MechanismFRCA Final

A 55-year-old man (ASA III) has chronic neuropathic pain from a brachial plexus injury. He is on pregabalin 300 mg BD and duloxetine 60 mg OD. His pain is 5/10. He is offered a trial of transcutaneous electrical nerve stimulation (TENS). What is the mechanism of analgesia from TENS?

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Correct answer: B — Gate control theory – stimulation of large Aβ fibres inhibits nociceptive C-fibre transmission at the spinal cord dorsal horn

TENS provides analgesia primarily through the gate control mechanism (Melzack & Wall, 1965). Electrical stimulation of large-diameter Aβ (touch/pressure) sensory fibres activates inhibitory interneurons in the dorsal horn of the spinal cord (substantia gelatinosa), which then inhibit transmission of nociceptive signals from small-diameter C-fibres and Aδ-fibres. High-frequency TENS (80-100 Hz) primarily acts through this segmental mechanism. Low-frequency TENS (2-4 Hz) may also activate descending pain modulation pathways and endogenous opioid release.

Reference: Faculty of Pain Medicine – 2021 – Non-pharmacological pain management; NICE – 2020 – CG173 Neuropathic pain