Pain
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In different fields of neuroscience research, illusions have successfully been used to unravel underlying mechanisms of stimulus processing. One such illusion existing for the field of pain research is the so-called thermal grill illusion. Here, painful sensations are elicited by interlacing warm and cold bars, with stimulus intensities (temperatures) of these bars being below the respective heat pain or cold pain thresholds. ⋯ Induction of sad, but not neutral mood states, resulted in higher pain and unpleasantness ratings of the painful illusion. These findings might be of importance for the understanding of pain processing in healthy volunteers, but putatively even more so in patients with major depressive disorder. Moreover, our results might indicate that central nervous structures involved in the affective domain or cognitive domain of pain processing might be involved in the perception of the illusion.
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The objective of this paper is to better understand the relationship of pain and mood in patients with fibromyalgia and comorbid major depressive disorder (MDD). Pooled data from 4 double-blind, placebo-controlled, randomized trials of duloxetine hydrochloride 60-120mg/day in patients with fibromyalgia were included (N=1332). Of these, 350 (26% [147 placebo, 203 duloxetine]) had comorbid MDD (per Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition Text Revision criteria) and were included in these analyses. ⋯ Results indicated that 69% of improvement in pain was a direct effect of treatment, with improvement in mood accounting for 31% of pain response. In conclusion, consistent with our hypothesis, duloxetine produced a substantial direct effect on pain improvement and change in mood exerted a modest indirect effect on pain improvements in patients with fibromyalgia and MDD. Hence, both direct and indirect analgesic and antidepressant properties appear to be relevant for the treatment of these comorbid patients with duloxetine.
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This is a revision of guidelines, originally published in 2004, for the assessment of patients with neuropathic pain. Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system either at peripheral or central level. Screening questionnaires are suitable for identifying potential patients with neuropathic pain, but further validation of them is needed for epidemiological purposes. ⋯ Skin biopsy to measure the intraepidermal nerve fiber density should be performed in patients with clinical signs of small fiber dysfunction. The intensity of pain and treatment effect (both in clinic and trials) should be assessed with numerical rating scale or visual analog scale. For future neuropathic pain trials, pain relief scales, patient and clinician global impression of change, the proportion of responders (50% and 30% pain relief), validated neuropathic pain quality measures and assessment of sleep, mood, functional capacity and quality of life are recommended.
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Multiple pathological mechanisms at multiple sensory sites may underlie the pain that follows nerve injury. This provides a basis for recommending more than one agent, either sequentially or in combination, for its treatment. According to this premise, new drugs that combine different mechanisms of analgesic action in a single molecule are gaining momentum, such as tapentadol which stimulates mu-opioid receptors (MOR) and acts as a noradrenaline reuptake inhibitor (NRI) in the CNS. ⋯ In particular, we performed a series of in vivo electrophysiological tests in spinal nerve ligated and sham-operated rats to show that systemic tapentadol (1 and 5mg/kg) dose-dependently reduced evoked responses of spinal dorsal horn neurones to a range of peripheral stimuli, including brush, punctate mechanical and thermal stimuli. Furthermore, we showed that spinal application of the selective α(2)-adrenoceptor antagonist atipamezole, or alternatively the mu-opioid receptor antagonist naloxone, produced near complete reversal of tapentadol's inhibitory effects, which suggests not only that the spinal cord is the key site of tapentadol's actions, but also that no pharmacology other than MOR-NRI is involved in its analgesia. Moreover, according to the extent that the antagonists reversed tapentadol's inhibitions in sham and SNL rats, we suggest that there may be a shift from predominant opioid inhibitory mechanisms in control animals, to predominant noradrenergic inhibition in neuropathic animals.
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Although various measures of low back pain (LBP) recurrence have been proposed, none have been tested to determine if they are consistent with what those with LBP perceive a "recurrence" to be. To further the understanding of LBP recurrence and how to measure it, we examined how individuals with a history of LBP describe their back pain experiences. A qualitative approach was chosen and six mixed-gender focus groups were conducted. ⋯ Three states were defined: "normal," "flared-up," and "attack." "Normal" could include experiencing pain, but generally represented a tolerable state. "Flared-up" was associated with increased pain, the use of strategies to overcome difficulties, and modified participation. "Attack" state was described as severely disabled: "I just have to lay there." Participants described their experiences in a way that is consistent with the idea that LBP is a fluctuating and disabling health condition. Results cast doubt on the validity of currently available measures of LBP recurrence. Focusing on recurrence of pain without consideration of broader contextual factors will result in an incomplete understanding of the meaning of the pain experience.