European journal of pain : EJP
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This study aims to assess whether the antinociceptive actions of methadone are mediated solely through opioid mechanisms, or whether its reported affinity for NMDA receptors has physiological relevance in vivo. Methadone is a mu-opioid receptor agonist reported to relieve pain unresponsive to other opioids. It is a racemic mixture comprising d- and l-optical isomers; the d-isomer has a lower affinity for opioid receptors, and both also exhibit NMDA receptor binding, likely to indicate antagonist activity. d -Methadone is antinociceptive in behavioural studies via non-opioid mechanisms, which could include functional NMDA receptor-blocking activity. ⋯ The inhibitory effects of both d - and dl -methadone on noxious-evoked activity were naloxone reversible. The naloxone reversibility of d -methadone inhibitions is best interpreted as indicative of a purely opioid mechanism of action. However, the ability of naloxone to reverse the effects of d -methadone may also reflect a degree of synergy between weak NMDA antagonist and opioid agonist activity.
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Despite the increasing popularity of intrathecal infusions to treat patients with long-term non-cancer-related pain, this therapy is not without serious side-effects. Five out of 23 patients who had intrathecal infusions of opiates for longer than 24 months developed leg and feet edema. As predisposing factors, cardiovascular disease, deep venous thrombosis, peripheral vascular disease, and venous stasis of the lower extremities were considered. ⋯ This complication was severe enough to limit their physical activity, and to produce lymphedema, ulcerations and hyperpigmentation of the skin. Reduction of the edema occurred when the dose of the opiate was decreased, and in two cases in which the infusion was discontinued, there was almost complete resolution of the syndrome. It appears that the pre-existence of pedal edema and of venous stasis is a relative contraindication to the long-term intrathecal infusion of opiates in patients with chronic non-cancer pain.
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To investigate the effect of chronic nociceptive pain on somatosensory perception, quantitative sensibility testing was performed in the most painful area and the homologous contralateral side in 14 patients with painful osteoarthritis of the hip. Twelve patients were reassessed in a painfree state 6-14 months following surgery. Von Frey filaments were used to test low-threshold mechanoreceptive function. ⋯ Compared to controls, patients had increased sensitivity to pressure pain in the most painful area (p < 0.002), bilaterally increased sensitivity to innocuous warmth (p < 0.03), cold pain (p< 0.05) and a tendency toward bilaterally increased sensitivity to heat pain (p = 0.054) before surgery. In the painful area, patients' sensitivity to pressure pain decreased (p < 0.04) and, remaining within normal limits, sensitivity to light touch increased (p < 0.006) compared to values prior to surgery. No statistically significant differences between the groups were seen following surgery, indicating that the sensibility changes had been maintained by chronic nociceptive pain.
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Comparative Study
Low frequency TENS is less effective than high frequency TENS at reducing inflammation-induced hyperalgesia in morphine-tolerant rats.
Both transcutaneous electrical nerve stimulation (TENS) and morphine are commonly used for relief of pain. Extensive research has been done on the effectiveness of each of these two methods for pain relief when given independently. However, very little literature exists examining the effectiveness of their combined use. ⋯ Both high (100 Hz) and low (4 Hz) frequency TENS caused nearly 100% inhibition of secondary hyperalgesia in animals receiving placebo pellets. In contrast, the hyperalgesia in morphine-tolerant animals with knee joint inflammation was unaffected by low frequency TENS but fully reversed by high frequency TENS. These results suggest that patients who are tolerant to morphine may respond better to high frequency TENS than to low frequency TENS.
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Historical Article
Validation of the German version of the Fear-Avoidance Beliefs Questionnaire (FABQ).
Fearful avoidance of physical activities is a major factor in low back pain (LBP) and disability. In 1993 Waddell et al. developed the Fear-Avoidance Beliefs Questionnaire (FABQ) focusing on patients' beliefs about how physical activity and work affect LBP. The focus of our study was to analyse and validate the German version of the FABQ. ⋯ Patients out of work demonstrated more fear-avoidance beliefs in comparison to those who were still working. It can be concluded that the German version of the FAQB is a reliable and valid instrument, but it shows a different factor structure from the original English version. The FABQ has been proven to identify patients with maladaptive beliefs which have to be focused on in proper treatment.