Abstract
Although chronic pain affects all age ranges, it is particularly common in the elderly. One potential explanation for the high prevalence of chronic pain in the older population is impaired functioning of the descending pain inhibitory system which can be studied in humans using conditioned pain modulation (CPM) paradigms. In this study we investigated (i) the influence of age on CPM and (ii) the role of expectations, depression and gender as potential modulating variables of an age-related change in CPM. 64 healthy volunteers of three different age groups (young = 20–40 years, middle-aged = 41–60 years, old = 61–80 years) were studied using a classical CPM paradigm that combined moderate heat pain stimuli to the right forearm as test stimuli (TS) and immersion of the contralateral foot into ice water as the conditioning stimulus (CS). The CPM response showed an age-dependent decline with strong CPM responses in young adults but no significant CPM responses in middle-aged and older adults. These age-related changes in CPM responses could not be explained by expectations of pain relief or depression. Furthermore, changes in CPM responses did not differ between men and women. Our results strongly support the notion of a genuine deterioration of descending pain inhibitory mechanisms with age.
Highlights
Chronic pain represents one of the largest medical health problems in the developed world and affects about 19% of the adult population [1]
In these paradigms pain intensity ratings of test stimuli ( = TS, e.g. heat pain stimuli applied to the arm) are obtained with and without concomitant application of a second pain stimulus that is applied to another part of the body
Positive conditioned pain modulation (CPM) responses, which are defined by a lower pain intensity rating for the test stimuli when they are applied in combination with the conditioning stimulus, are indicative of endogenous analgesia
Summary
Chronic pain represents one of the largest medical health problems in the developed world and affects about 19% of the adult population [1]. Chronic pain affects all age groups, it is common in the elderly population affecting more than 50% of the older adults and up to 80% of nursing home residents [2]. A well-established tool to study the descending pain control system in humans is the use of conditioned pain modulation (CPM) paradigms. In these paradigms pain intensity ratings of test stimuli ( = TS, e.g. heat pain stimuli applied to the arm) are obtained with and without concomitant application of a second pain stimulus (i.e., the conditioning stimulus = CS) that is applied to another part of the body (e.g. a cold pressor task applied to the leg). CPM responses in humans have been shown to underlie cognitive manipulations [8] and to involve higher cortical brain areas such as the cingulate and frontal cortex [9,10,11]
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