Pain
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Patellofemoral pain (PFP) is a common and recurrent knee condition in young females, characterized by pressure hyperalgesia and reduced pain inhibitory control. This study investigated antinociceptive and pronociceptive profiles in young females with long-standing (>5 years) PFP (current-PFP), those who recovered from adolescent PFP (recovered-PFP), and pain-free controls. This preregistered, assessor-blinded, cross-sectional study included 87 females younger than 25 years: 36 current-PFP, 22 recovered-PFP, and 29 pain-free controls. ⋯ Compared with controls, the recovered-PFP also had reduced pressure pain thresholds at the knee, which were higher than the current-PFP (mean difference: 110-225 kPa; P < 0.05). In conclusion, both current-PFP and recovered-PFP displayed altered pain mechanisms compared to controls with no history of knee pain, despite resolution of symptoms in the recovered-PFP group. The implications of these findings in the recurrent nature of PFP requires further studies.
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Conditioned pain modulation (CPM) and temporal summation of pain (TSP) are 2 experimental paradigms capturing endogenous pain modulation, which have repeatedly demonstrated clinical relevance. Conditioned pain modulation describes the inhibition of the pain response to a test stimulus (Ts) when a second noxious stimulus, the conditioning stimulus (CS), is concurrently applied. Temporal summation of pain describes the enhanced pain response to a series of stimuli compared with single stimuli. ⋯ Interestingly, this interaction was modality-dependent: TSP for heat Ts was completely abolished by CPM, whereas this was not the case for pressure Ts. Our findings suggest different forms of central sensitization induced by TSP using either heat or pressure stimuli, which differ in their susceptibility to CPM. Clinical implications and directions for future research are discussed.
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The placebo effect is considered the core example of mind-body interactions. However, individual differences produce large placebo response variability in both healthy volunteers and patients. The placebo response in pain, placebo analgesia, may be dependent on both the opioid system and the dopaminergic system. ⋯ Participants with OPRM1 Asn/Asn combined with COMT Met/Met and Val/Met reported significant pain relief after placebo administration, whereas those with other combinations of the OPRM1 and COMT genotypes displayed no significant placebo effect. Neither OPRM1 nor COMT had any significant influence on affective changes after placebo administration. As shown in this study, genotyping with regard to OPRM1 and COMT may predict who will respond favorably to placebo analgesic treatment.
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Interindividual differences in pain sensitivity vary as a function of interactions between sensory, cognitive-affective, and dispositional factors. Trait mindfulness, characterized as the innate capacity to nonreactively sustain attention to the present moment, is a psychological construct that is associated with lower clinical pain outcomes. Yet, the neural mechanisms supporting dispositional mindfulness are unknown. ⋯ Whole brain analyses revealed that higher dispositional mindfulness was associated with greater deactivation of a brain region extending from the precuneus to posterior cingulate cortex during noxious heat. These novel findings demonstrate that mindful individuals feel less pain and evoke greater deactivation of brain regions supporting the engagement sensory, cognitive, and affective appraisals. We propose that mindfulness and the posterior cingulate cortex should be considered as important mechanistic targets for pain therapies.