Abstract
Intramuscular injection of hypertonic saline produces a dull ache that is felt in
the muscle belly but also often refers into distal structures. We have previously
observed in 2 subjects that the pattern of pain referral alters during painful stimuli
separated by a week. In this investigation, we tested the hypothesis that the intensity
and area of pain in the local and referred regions exhibits plasticity when an identical
noxious stimulus is delivered to the same site over sequential trials. Bolus 1 mL
intramuscular injections of 5% hypertonic saline were made into the same site of the
tibialis anterior (TA) muscle on the same day each week for 4 consecutive weeks. Twenty-one
subjects mapped the areas of local and referred pain and rated the intensities on
a visual analog scale every 30 seconds until the cessation of pain. Over 4 weeks there
was a progressive reduction in the area and intensity of local pain and a reciprocal
increase in the expression of referred pain. We conclude that the decrease in perceived
local pain and increase in perceived referred pain reflects plastic processes occurring
centrally.
Perspective
What happens to the intensity of pain induced by repeated noxious stimuli over time?
Does it stay the same, increase or decrease? Here we show that weekly injections of
hypertonic saline into the tibialis anterior cause decreases in local but increases
in referred pain, suggesting central changes in processing noxious inputs.
Key words
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Article info
Publication history
Published online: March 15, 2010
Accepted:
November 9,
2009
Received in revised form:
October 17,
2009
Received:
June 8,
2009
Footnotes
Supported by the National Health and Medical Research Council of Australia (Project Grant 350889).
Identification
Copyright
© 2010 American Pain Society. Published by Elsevier Inc. All rights reserved.
