Pain
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Recent studies indicate that aging is associated with dysfunctional changes in pain modulatory capacity, potentially contributing to increased incidence of pain in older adults. However, age-related changes in offset analgesia (offset), a form of temporal pain inhibition, remain poorly characterized. The purpose of this study was to investigate age differences in offset analgesia of heat pain in healthy younger and older adults. ⋯ Interestingly, offset analgesia was nonexistent on the palm for all subjects. The reduced offset found in older adults may reflect an age-related decline in endogenous inhibitory systems. However, although the exact mechanisms underlying offset remain unknown, the absence of offset at the palm suggests that peripheral mechanisms may be involved in initiating this phenomenon.
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Patients receiving opioids for pain may experience decreased effectiveness of the drug and even abnormal pain sensitivity-hyperalgesia and/or allodynia. We hypothesized that peripheral nociceptor hyperexcitability contributes to opioid-induced hyperalgesia and tested this using an in vitro mouse glabrous skin-nerve preparation. Mice were injected intraperitoneally with escalating doses of morphine (5, 8, 10, 15 mg/kg) or saline every 12 hours for 48 hours and killed approximately 12 hours after the last injection. ⋯ In morphine-treated mice, aberrant activity and hyperexcitability of nociceptors could contribute to increased pain sensitivity. Importantly, this activity is likely driving central sensitization, a phenomenon contributing to abnormal sensory processing and chronic pain. If similar changes occur in human patients, aberrant nociceptor activity is likely to be interpreted as pain and could contribute to opioid-induced hyperalgesia.
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The clinical effects of motor cortex stimulation (MCS) for neuropathic pain (NP) is thought to be mediated primarily by the secretion of endogenous opioids in humans and in animal models. Because opioid receptor density is itself decreased in patients with NP, we investigated whether the magnitude and distribution of the remaining opioid receptors in patients with NP could be biological predictors of the pain-relieving effects of MCS. Using (11)C-diprenorphine positron emission tomography scans, opioid receptor availability was assessed in 15 patients suffering refractory NP, who subsequently received chronically implanted MCS. ⋯ The levels of preoperative opioid-binding in the insula, thalamus, periaqueductal gray, anterior cingulate, and orbitofrontal cortex were significantly and positively correlated with postoperative pain relief at 7mo. Patients with receptor density values below the lower limits in age-matched controls in the thalamus, periaqueductal gray and contralateral insula were the least likely to benefit from MCS. Opioid-receptor availability as shown in preoperative positron emission tomography scans appears to be related to the efficacy of MCS in NP and may help clinicians to select the candidates most likely to benefit from this procedure.
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The expression of pain is altered in people with dementia (PWD), increasing the risk of undertreatment in that population. The objective of this study was to determine whether dementia and the absence of pain assessment in the patients' medical chart reduced the probability of analgesic use in a large sample of nursing home (NH) residents. This is a cross-sectional study using data from 6275 residents (mean age 86 ± 8.2 years; 73.7% women) from 175 NHs located in France. ⋯ Results remained fairly unchanged after performing several sensitivity analyses. Our results suggest that improvements are needed in pain management in NHs, particularly for PWD. Implementing systematic evaluations of pain in NHs' routine would contribute to a better management of pain, which can lead to important benefits for residents.