Highlights
- •Lack of transcutaneous electrical nerve stimulation (TENS) induced thermal analgesia in the absence of capsaicin-evoked sensitization.
- •Capsaicin unmasks the analgesic effect of conventional TENS on thermal sensitivity.
- •TENS analgesia is possibly caused by interactions with sensitized small-diameter fibers.
- •Extrasegmental TENS had no effect on thermal sensitivity indicating spinal effect.
Abstract
Although nonnoxious, high-frequency electrical stimulation applied segmentally (ie,
conventional transcutaneous electrical nerve stimulation [TENS]) has been proposed
to modulate pain, the mechanisms underlying analgesia remain poorly understood. To
further elucidate how TENS modulates pain, we examined evoked responses to noxious
thermal stimuli after the induction of sensitization using capsaicin in healthy volunteers.
We hypothesized that sensitization caused by capsaicin application would unmask TENS
analgesia, which could not be detected in the absence of sensitization. Forty-nine
healthy subjects took part in a series of experiments. The experiments comprised the
application of topical capsaicin (.075%) on the left hand in the C6 dermatome, varying
the location of TENS (segmental, left C6 dermatome, vs extrasegmental, right shoulder),
and assessing rating of perception (numeric rating scale: 0–10) and evoked potentials
to noxious contact heat stimuli. The extrasegmental site was included as a control
condition because previous studies indicate no analgesic effect to remote conventional
TENS. Conventional TENS had no significant effect on rating or sensory evoked potentials
in subjects untreated with capsaicin. However, segmental TENS applied in conjunction
with capsaicin significantly reduced sensation to noxious thermal stimuli following
a 60-minute period of sensitization.
Perspective
The study indicates that sensitization with capsaicin unmasks the analgesic effect
of conventional TENS on perception of noxious contact heat stimuli. Our findings indicate
that TENS may be interacting segmentally to modulate distinct aspects of sensitization,
which in turn results in analgesia to thermal stimulation.
Key words
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Article info
Publication history
Published online: April 09, 2015
Accepted:
March 13,
2015
Received in revised form:
February 16,
2015
Received:
November 17,
2014
Footnotes
Supported by the Swiss National Science Foundation (SNF320030 135558) and the Clinical Research Priority Program “Neurorehab” of the University of Zurich, Switzerland. J.L.K.K. was supported by postdoctoral funding from the International Foundation for Paraplegia–Zurich.
The authors report no conflict of interests.
Identification
Copyright
© 2015 American Pain Society. Published by Elsevier Inc. All rights reserved.
