Decreased Initial Peak Pain Sensation with Aging: A Psychophysical Study.

BACKGROUND AND PURPOSE: Aging is associated with an impairment of diverse physiological functions, including nociception. For example, older adults in comparison to young adults, show an overall increase in pain thresholds, reflecting a decline in pain sensitivity and changes in the nociceptive pathways. These results are, however, debated as they were not always replicated depending on the stimulus modality, duration, and location. The aim of the current study was to determine how the temporal evolution of pain intensity during a continuous tonic heat pain test is influenced by aging. More specifically, we wanted to 1) assess the effect of age on initial peak and late-phase pain and 2) determine whether potential age effects depend on the stimulation site. PARTICIPANTS AND METHODS: 13 young adults (average of 27.9 years old) and 13 older adults (average of 67.5 years old) participated in this study. Experimental heat pain was evoked on an appendicular (forearm) and axial (lower-back) body region, using a thermode (2-minute stimulation at a constant, individually-adjusted temperature). During the nociceptive stimulation, participants used a computerized visual analogue scale to continuously rate their pain. RESULTS: We show that initial peak (0-30 seconds) pain sensation was significantly lower in older adults compared to young adults, while late-phase (30-120 seconds) pain sensation was similar across the two age groups. These results hold true for both stimulation sites, suggesting the existence of an age effect on both appendicular and axial body regions. CONCLUSION: The lower magnitude of initial peak pain observed in older adults, which affects both appendicular and axial body regions, could reflect generalized peripheral or central alterations of the nociceptive system in older adults. These alterations in older adults could have significant clinical impacts, such as an increased vulnerability to injury or an underestimation of the severity of their pain condition.

Transcutaneous electrical nerve stimulation and placebo analgesia: is the effect the same for young and older individuals?

PURPOSE: Placebo analgesia refers to a perceived reduction in pain intensity following the administration of a simulated or otherwise medically ineffective treatment. Previous studies have shown that many factors can influence the magnitude of placebo analgesia. However, few investigations have examined the effect of age on placebo analgesia, and none have done it in the context of electrotherapeutic interventions. The objective of this study is to compare the placebo response induced by sham transcutaneous electrical nerve stimulation (TENS) between young and older individuals, using an experimental heat-pain paradigm. PATIENTS AND METHODS: Twenty-two young (21-39 years) and 22 older (58-76 years) healthy adults participated in this comparative study. Experimental heat pain was evoked with a thermode (2-min stimulation at a constant individually adjusted temperature) applied on the lumbar region. Participants were asked to evaluate the intensity of their pain using a computerized visual analog scale. Experimental pain was induced before and after an unconditioned placebo intervention (placebo TENS) applied for 25 min. RESULTS: In young individuals, no significant pain reductions were noted, whereas in older individuals, a statistically significant pain reduction was observed after the placebo stimulation (P<0.01). Between-group analyses revealed that placebo analgesia was greater in older individuals (40% pain reduction) compared with young individuals (15% pain reduction) (P<0.05). However, sham TENS increased heat-pain thresholds in the young group (P<0.01), but not in the older group (P=0.43). CONCLUSION: Our results indicate that placebo analgesia is influenced by age, with older individuals showing larger placebo analgesia than young adults. Although these results should be confirmed in clinical pain populations, the current observations bear potentially important consequences for the design of future placebo-controlled trials and for healthcare professionals working with elderly patients.

Adjusting Pulse Amplitude During Transcutaneous Electrical Nerve Stimulation Does Not Provide Greater Hypoalgesia.

OBJECTIVES: Transcutaneous electrical nerve stimulation (TENS) is an electrotherapeutic modality commonly used in rehabilitation to relieve pain. Adjusting pulse amplitude (intensity) during TENS treatment has been suggested to overcome nerve habituation. However, it is still unclear if this procedure leads to greater hypoalgesia. The aim of this study was to determine if the hypoalgesic effect of TENS is greater when pulse amplitude is adjusted throughout the TENS treatment session in chronic low-back pain patients. DESIGN: Randomized double-blind crossover study. SETTING: Recruitment and assessment were conducted at the Clinique universitaire de réadaptation de l'Estrie (CURE) of the Faculty of Medicine and Health Sciences of the Université de Sherbrooke. PARTICIPANTS: Twenty-one volunteers with chronic low-back pain were enrolled and completed this investigation. INTERVENTIONS: Each patient received two high-frequency TENS treatments on two separate sessions: (1) with adjustment of pulse amplitude and (2) without pulse amplitude adjustment. MAIN OUTCOME MEASURES: Pain intensity and unpleasantness were assessed before, during, and after TENS application with a 10 cm visual analog scale. RESULTS: Both TENS conditions (with and without adjustment of intensity) decreased pain intensity and unpleasantness when compared with baseline. No difference was observed between the two stimulation conditions for both pain intensity and unpleasantness. CONCLUSION: The current results suggest that adjustment of pulse amplitude during TENS application does not provide greater hypoalgesia in individuals with chronic low-back pain. Future studies are needed to confirm these findings in other pain populations.

Can We Quickly and Thoroughly Assess Pain with the PACSLAC-II? A Convergent Validity Study in Long-Term Care Residents Suffering from Dementia.

A previous study found that the modified version of the Pain Assessment Checklist for Seniors with Limited Ability to Communicate (PACSLAC-II) is a valid tool to assess pain in elderly individuals suffering from dementia and who are unable to communicate verbally. The primary objective of this study was to confirm the convergent validity of the PACSLAC-II using direct evaluation of long-term care residents in real-life situations, using two other well-validated pain assessment scales (i.e., PACSLAC and Pain Assessment in Advanced Dementia [PAINAD]). A secondary objective was to document and compare the time required to complete and score each assessment scale. During two potentially painful procedures (i.e., transfer/mobilization), 46 long-term care residents (mean age = 83 ± 10 years) suffering from dementia were observed by three independent evaluators, each using one of the assessment scales (randomly assigned). Correlational analyses and analysis of variance were used to evaluate the association between each scale and to compare scoring time. The PACSLAC (r = 0.61) and the PAINAD (r = 0.65) were both moderately associated with the PACSLAC-II (all p values < .001). The PAINAD's average scoring time (63 ± 19 seconds) was lower than the PACSLAC-II's (96 ± 2 seconds), which was lower than the PACSLAC's (135 ± 53 seconds) (all p values < .001). These results suggest that the PACSLAC-II is a valid tool for assessing pain in individuals with dementia. The time required to complete and score the PACSLAC-II was reasonable, supporting its usefulness in clinical settings.

Can we improve pain and sleep in elderly individuals with transcranial direct current stimulation? - Results from a randomized controlled pilot study.

BACKGROUND: The prevalence of chronic pain and sleep disturbances substantially increases with age. Pharmacotherapy remains the primary treatment option for these health issues. However, side effects and drug interactions are difficult to control in elderly individuals. AIMS: The objective of this study was to assess the feasibility of conducting a randomized sham-controlled trial and to collect preliminary data on the efficacy of transcranial direct current stimulation (tDCS) to reduce pain and improve sleep in older adults suffering from chronic pain. METHODS: Fourteen elderly individuals (mean age 71±7 years) suffering from chronic pain and sleep complaints were randomized to receive either anodal tDCS, applied over the primary motor cortex (2 mA, 20 minutes), or sham tDCS, for 5 consecutive days. Pain was measured with visual analog scales, pain logbooks and questionnaires, while sleep was assessed with actigraphy, sleep diaries and questionnaires. RESULTS: There were no missing data for pain and sleep measures, except for actigraphy, that generated several missing data. Blinding was maintained throughout the study, for both the evaluator and participants. Active but not sham tDCS significantly reduced pain (P<0.05). No change was observed in sleep parameters, in both the active and sham tDCS groups (all P≥0.18). CONCLUSION: The present study provides guidelines for the implementation of future tDCS studies in larger populations of elderly individuals. M1 anodal tDCS in this population appears to be effective to reduce pain, but not to improve sleep.

High- and low-frequency transcutaneous electrical nerve stimulation does not reduce experimental pain in elderly individuals.

Despite its widespread clinical use, the efficacy of transcutaneous electrical nerve stimulation (TENS) remains poorly documented in elderly individuals. In this randomized, double-blind crossover study, we compared the efficacy of high-frequency (HF), low-frequency (LF), and placebo (P) TENS in a group of 15 elderly adults (mean age: 67 ± 5 years). The effect of HF-, LF-, and P-TENS was also evaluated in a group of 15 young individuals (26 ± 5 years; same study design) to validate the effectiveness of the TENS protocols that were used in the elderly group. Each participant came to the laboratory on 3 separate occasions to receive, in random order, HF-, LF-, and P-TENS. Pain intensity and pain perception thresholds were assessed before, during, and after TENS, using an experimental heat pain paradigm. For the young group, there was a significant decrease in pain intensity during and after HF- and LF-TENS when compared with baseline, with both HF- and LF-TENS being superior to P-TENS. In the older group, HF- and LF-TENS did not reduce pain when compared with baseline and no difference was observed between the 2 active TENS sessions and P-TENS. High-frequency, LF-, and P-TENS all increased pain thresholds in young individuals, whereas in older individuals, only LF-TENS increased pain thresholds. Taken together, these results suggest that TENS is effective in young, but not in older, individuals. Future studies should be conducted to confirm these results in pain populations and to identify strategies that could enhance the effect of TENS in the elderly.