Pain
-
Comparative Study
Individual differences in pain sensitivity: genetic and environmental contributions.
Large individual differences in pain sensitivity present a challenge for medical diagnosis and may be of importance for the development of chronic pain. Variance in pain sensitivity is partially mediated by genetic factors, but the extent of this contribution is uncertain. We examined cold-pressor pain and contact heat pain in 53 identical (MZ) and 39 fraternal (DZ) twin pairs, and 4 single twins to determine the heritability of the two phenotypes, and the extent to which the same genetic and environmental factors affect both pain modalities. ⋯ These findings demonstrate that cold-pressor pain and contact heat pain are mainly distinct phenomena from both a genetic and an environmental standpoint. This may partly explain disparate results in genetic association studies and argues for caution in generalizing genetic findings from one pain modality to another. It also indicates that differences in pain scale usage account for a minor portion of the variance, providing strong support for the validity of subjective pain ratings as measures of experienced pain.
-
The nocebo effect consists in delivering verbal suggestions of negative outcomes so that the subject expects clinical worsening. Here we show that nocebo suggestions, in which expectation of pain increase is induced, are capable of producing both hyperalgesic and allodynic responses. By extending previous findings on the placebo effect, we investigated the role of learning in the nocebo effect by means of a conditioning procedure. ⋯ Therefore, in contrast to placebo analgesia, whereby a conditioning procedure elicits larger effects compared to verbal suggestions alone, learning seems to be less important in nocebo hyperalgesia. Overall, these findings indicate that, by defining hyperalgesia as an increase in pain sensitivity and allodynia as the perception of pain in response to innocuous stimulation, nocebos can indeed produce both hyperalgesic and allodynic effects. These results also suggest that learning is not important in nocebo hyperalgesia compared to placebo analgesia.
-
Descending modulation of pain can be demonstrated psychophysically by dual pain stimulation. This study evaluates in 31 healthy subjects the association between parameters of the conditioning stimulus, gender and personality, and the endogenous analgesia (EA) extent assessed by diffuse noxious inhibitory control (DNIC) paradigm. Contact heat pain was applied as the test stimulus to the non-dominant forearm, with stimulation temperature at a psychophysical intensity score of 60 on a 0-100 numerical pain scale. ⋯ Importantly, pain scores of the conditioning stimuli were not correlated with EA extent. The latter is based on both our study population, and on additional 82 patients, who participated in another study, in which EA was induced by immersion at 46.5 degrees C. DNIC testing, thus, seems to be relatively independent of the stimulation conditions, making it an easy to apply tool, suitable for wide range applications in pain psychophysics.
-
Randomized Controlled Trial Comparative Study
Predicting outcome of TENS in chronic pain: a prospective, randomized, placebo controlled trial.
Transcutaneous electrical nerve stimulation (TENS) is an easy to use non-invasive analgesic intervention applied for diverse pain states. However, effects in man are still inconclusive, especially for chronic pain. Therefore, to explore the factors predicting result of TENS treatment in chronic pain we conducted a prospective, randomized, placebo-controlled trial (n=163), comparing high frequency TENS (n=81) with sham TENS (n=82). Patients' satisfaction (willingness to continue treatment; yes or no) and pain intensity (VAS) were used as outcome measures. The origin of pain and cognitive coping strategies were evaluated as possible predictors for result of TENS treatment. ⋯ Fifty-eight percent of the patients in the TENS group and 42.7% of the sham-TENS group were satisfied with treatment result (chi square=3.8, p=0.05). No differences were found for pain intensity. Patients diagnosed with osteoarthritis and related disorders (especially of the vertebral column) or peripheral neuropathic pain were less satisfied with high frequency TENS (OR=0.12 (95% CI 0.04-0.43) and 0.06 (95% CI 0.006-0.67), respectively). Injury of bone and soft tissue (especially postsurgical pain disorder) provided the best results. Treatment modality or interactions with treatment modality did not predict intensity of pain as a result of treatment. We conclude, that predicting the effect of high frequency TENS in chronic pain depends on the choice of outcome measure. Predicting patients' satisfaction with treatment result is related to the origin of pain. Predicting pain intensity reflects mechanisms of pain behavior and perceived control of pain, independent of treatment modality. Pain catastrophizing did not predict TENS treatment outcome.
-
In many countries timely access to care is a growing problem. As medical costs escalate health care resources must be prioritized. In this context there is an increasing need for benchmarks and best practices in wait-time management. ⋯ It was concluded that wait-times for chronic pain treatment of 6 months or longer are medically unacceptable. Further study is necessary to determine at what stage the deterioration begins from the onset of pain to treatment and the impact of waiting on treatment outcomes. Most important is the need to improve access to appropriate care for patients with chronic pain, an escalating public health care problem with significant human and economic costs.