Highlights
- •Ninety-three percent of healthy subjects exhibit a meaningful conditioned pain modulation (CPM) effect.
- •There is no gender difference in CPM effect.
- •CPM effect does not appear to depend on the intensity of the conditioning stimulus, provided it is sufficiently noxious.
Abstract
Conditioned pain modulation (CPM) encompasses the effects of inhibitory and facilitatory
pain modulatory systems and is inefficient in some chronic pain states. A proportion
of healthy subjects also exhibit little or no CPM, perhaps suggesting that inherent
factors such as gender or genetics may be influential. However, there is no consensus
on how best to determine a meaningful CPM effect. This study aimed to determine the
proportion of pain-free subjects exhibiting a meaningful CPM effect. Analyses of associations
between 5HTTLPR (serotonin transporter-linked polymorphic region) polymorphisms on
the serotonin transporter gene (SLC6A4), gender, and CPM effect were also carried out. A total of 125 healthy subjects (47
male; 78 female) underwent pressure pain threshold testing before, during, and after
a cold pressor conditioning stimulus. A buccal cell sample was collected for analysis
of 5HTTLPR genotype. Meaningful CPM effect was determined as an increase in pressure
pain threshold values from baseline greater than the inherent error of measurement,
calculated as 5.3%. During the conditioning stimulus, 116 subjects (92.8%) exhibited
a CPM effect whereas 9 did not. CPM effect did not differ significantly between genders
or between 5HTTLPR genotypes. This provides a clear basis on which to determine the
proportion of patients with a chronic pain disorder that exhibit a meaningful CPM
effect.
Perspective
This study proposes a method for calculating meaningful CPM effect and reports the
proportion and magnitude of effect elicited in a large sample. Associations between
CPM, gender, and genotype were also analyzed. Clarification of normal CPM response
may help to elucidate the mechanisms driving CPM inefficiency in chronic pain.
Key words
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Article info
Publication history
Published online: September 18, 2014
Accepted:
September 1,
2014
Received in revised form:
August 20,
2014
Received:
April 2,
2014
Footnotes
All work completed at Curtin University.
This study was supported by a Curtin University Faculty of Health Sciences, Bioscience and Clinical Sciences Collaboration Grant.
There were no benefits received in any form from a commercial party related directly or indirectly to the subject of this manuscript, nor will there be. No conflicts of interest exist for any of the authors.
Identification
Copyright
© 2014 Published by Elsevier Inc. All rights reserved.
