Individual responder analyses for pain: does one pain scale fit all?

Pain sensitivity can be assessed by self-rating: Development and validation of the Pain Sensitivity Questionnaire

Experimental determination of pain sensitivity has received increasing attention because of emerging clinical applications (including prediction of postoperative pain and treatment response) and scientific implications (e.g. it has been proposed that above-average pain sensitivity is a risk factor for the development of chronic pain disorders). However, the use of experimental pain sensitivity assessment on a broad scale is hampered by its requirements on time, equipment and human resources and the fact that it is painful for the tested subject. Alternatives to experimental pain testing are currently lacking. Here we developed a self-rating instrument for the assessment of pain sensitivity, the Pain Sensitivity Questionnaire (PSQ) that is based on pain intensity ratings of daily life situations and takes 5-10min to complete. Adequate reliability of the PSQ was confirmed in 354 subjects. In a validation study comprising 47 healthy subjects, the results of comprehensive experimental pain testing, including different modalities (heat, cold, pressure, and pinprick) and different measures (pain thresholds, pain intensity ratings), were compared to the results of the PSQ. PSQ scores were significantly correlated to experimental pain intensity ratings (r = 0.56, p < 0.001) but not to pain thresholds (r = 0.03). Prediction of experimental pain intensity ratings by the PSQ was better than by pain-associated psychological factors (pain catastrophizing, depression, anxiety). This shows that the PSQ may be a simple alternative to experimental pain intensity rating procedures in healthy subjects and makes the PSQ a highly promising tool for clinical and experimental pain research.

Genetic contributions to clinical pain and analgesia: avoiding pitfalls in genetic research

Understanding the genetic basis of human variations in pain is critical to elucidating the molecular basis of pain sensitivity, variable responses to analgesic drugs, and, ultimately, to individualized treatment of pain and improved public health. With the help of recently accumulated knowledge and advanced technologies, pain researchers hope to gain insight into genetic mechanisms of pain and eventually apply this knowledge to pain treatment.

PERSPECTIVE

We critically reviewed the published literature to examine the strength of evidence supporting genetic influences on clinical and human experimental pain. Based on this evidence and the experience of false associations that have occurred in other related disciplines, we provide recommendations for avoiding pitfalls in pain genetic research.

Sex differences in prior pain experience

Sex differences in clinical and experimental pain experiences are well documented. However, there has been little work investigating men's and women's experiences with common painful events. This study examined sex differences in the nature and intensity of common pain experiences. Participants (102 women and 85 men) completed the Prior Pain Experience Questionnaire, which is a 79-item assessment of an individual's pain experience, recalled pain ratings, and imagined pain ratings. Analyses of variance were conducted to assess for sex differences in overall pain experience and pain ratings. Men and women did not have significant differences in the overall number of reported pain experiences or in the overall mean pain rating of those experiences. However, they differed in specific pain events experienced (eg, men experienced concussions more than women) and pain ratings (eg, women rated minor surgery as significantly more painful than men). Individuals who imagined pain events tended to rate them as equally or more painful than individuals who experienced those pain events.

PERSPECTIVE

Results of this study demonstrate that men and women have varying types of pain experiences without evidence that the overall pain experience differs between sexes. It was also found that imagined pain ratings are often worse than experienced pain ratings, lending support for the tendency of individuals to catastrophize.

Pain responder analysis: use of area under the curve to enhance interpretation of clinical trial results

Interpretation of results on patient-reported pain outcomes from clinical trials should be meaningful to patients and healthcare providers. This study applied an area-under-the-curve (AUC) analysis to responder profiles in a clinical trial of pregabalin for the treatment of fibromyalgia (FM). Data were from a 14-week, randomized, placebo-controlled trial of pregabalin (300, 450, or 600 mg/day) for the treatment of FM in patients meeting American College of Rheumatology criteria for FM and with a baseline pain score of at least 40 mm on the 100-mm pain visual analogue scale. Pain was evaluated in a daily diary by patients using an 11-point numeric rating scale (0 = no pain, 10 = worst possible pain). Response profiles on pain improvement scores and their differences between pregabalin and placebo were assessed using the AUC (derived using the trapezoidal rule) from the responder curve (vertical axis, proportion of subjects; horizontal axis, minimum percent improvement in pain). The AUC can be interpreted as if all responders were improved by the same percentage equal to the AUC divided by 100. The AUCs (2,100 for placebo, and 2,944, 3,170, and 3,349 for pregabalin 300, 450, and 600 mg, respectively) can be considered as if every responder improved by 21, 29, 31, and 33.5% in the responder's respective treatment group. Pain improvement was significantly better with pregabalin (P < 0.05), with pregabalin responders improving by 8.4% (300 mg/day), 10.7% (450 mg/day), and 12.5% (600 mg/day) more than placebo responders. This novel approach demonstrates that responder profiles can provide an enhanced interpretation of pain outcomes for patient care and symptom management.

Do interference-based cut-points differentiate mild, moderate, and severe levels of 16 cancer-related symptoms over time?

In our previous work, we established interference-based cut-points to differentiate moderate from mild, and severe from moderate levels of severity for 16 symptoms as reported by cancer patients undergoing chemotherapy. This work examines how consistent the differentiation is over time. If the levels of severity successfully differentiate interference scores over time, then anchor-based categories can be developed to evaluate patients' responses to the intervention. To test the differentiation of the interference scores by the three severity categories, data from two symptom management trials were used. Five hundred and ninety-nine patients were queried at each of the six contacts that occurred over eight weeks as to the severity of each of the 16 symptoms on the scale from 0 (not present) to 10 and the extent to which each symptom interfered with enjoyment of life, relationships with others, general daily activities and emotions. Longitudinal models that related interference scores to severity levels of symptoms were used. Differences among adjusted mean interference scores for mild, moderate, and severe levels were tested at each contact. Differences among interference-based severity categories were consistent over time and clinically important, and thus can be used to anchor changes in symptom severity.

Metallic taste phantom predicts oral pain among 5-year survivors of head and neck cancer

Chronic pain following cancer-related treatment is emerging as a major concern. Heretofore, the pain level among 5-year survivors of head and neck cancer has received limited attention. This study proposes a predictive model for understanding factors associated with the elevated levels of chronic oral pain. Cancer survivors were drawn from a pool of 5-year survivors. A listed sample matched on sex, age, and zip code was purchased and served as a comparison group. Telephone interviews were conducted by a professional call center. Oral pain levels and the presence of metallic taste phantoms were significantly higher in the cancer survivor group than among the comparison group. The prevalence of chronic oral pain among the 5-year survivors was 43% compared to 13% for the comparison group. Hierarchical linear regression showed that among the 5-year survivors, the predictive model for spontaneous pain accounted for 24% of the variance, and for function-related pain the model accounted for 34% of the variance, with the presence of a phantom metallic taste making a significant independent contribution in both models. In the function-related pain model, depression and level of oral function quality of life (QOL) made significant independent contributions. The presence of oral pain is a significant problem among head and neck cancer survivors. The presence of metallic phantoms is an important new piece of evidence suggesting neural damage following cancer-directed treatment. Routine assessment of oral pain levels could improve current analgesic approaches among head and neck cancer survivors.

Ethnic differences in diffuse noxious inhibitory controls

Substantial evidence indicates that the experience of both clinical and experimental pain differs among ethnic groups. Specifically, African Americans generally report higher levels of clinical pain and greater sensitivity to experimentally induced pain; however, little research has examined the origins of these differences. Differences in central pain-inhibitory mechanisms may contribute to this disparity. Diffuse noxious inhibitory controls (DNIC), or counterirritation, is a phenomenon thought to reflect descending inhibition of pain signals. The current study assessed DNIC in 57 healthy young adults from 2 different ethnic groups: African Americans and non-Hispanic whites. Repeated assessments of the nociceptive flexion reflex (NFR) as well as ratings of electrical pain were obtained before, during, and after an ischemic arm pain procedure (as well as a sham procedure). The DNIC condition (ie, ischemic arm pain) produced substantial reductions in pain ratings as well as electrophysiologic measures of the NFR for all participants when compared with the sham condition (P < .001). The DNIC condition produced significantly greater reductions in verbal pain ratings among non-Hispanic whites when compared with African Americans (P = .02), whereas ethnic groups showed comparable reductions in NFR. The findings of this study suggest differences in endogenous pain inhibition between African Americans and non-Hispanic whites and that additional research to determine the mechanisms underlying these effects is warranted.

PERSPECTIVE

This study adds to the growing literature examining ethnic differences in experimental pain perception. Our data suggest that these variations may be influenced by differences in descending inhibition.

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. An estimated 60% of the variance in cold-pressor pain and 26% of the variance in heat pain was genetically mediated. Genetic and environmental factors were only moderately correlated across pain modalities. Genetic factors common to both modalities explained 7% of the variance in cold-pressor and 3% of the variance in heat pain. Environmental factors common to both modalities explained 5% of variance in cold-pressor and 8% of the variance in heat pain. The remaining variance was due to factors that were specific to each pain modality. 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.

Establishing mild, moderate, and severe scores for cancer-related symptoms: how consistent and clinically meaningful are interference-based severity cut-points?

Methods are presented to separate 16 frequently occurring cancer symptoms measured on 10-point symptom severity rating scales into mild, moderate, and severe categories that are clinically interpretable and significant for use in oncology practice settings. At their initial intervention contact, 588 solid tumor cancer patients undergoing chemotherapy reported severity on a standard 11-point rating scale for 16 symptoms. All reporting a one or higher were asked to rate on an 11-point scale how much the symptom interfered with enjoyment of life, relationship with others, general daily activities, and emotions. Factor analysis revealed that these items tapped into the same dimension, and the items were summed to form an interference scale. Cut-points for mild, moderate, and severe categories of symptom severity were defined by comparing the differences in interference scores corresponding to each successive increases in severity for each symptom. The cut-points differed among symptoms. Pain, fatigue, weakness, cough, difficulty remembering, and depression had lower cut-points for each category compared to other symptoms. Cut-points for each symptom were not related to site or stage of cancer, age, or gender but were associated with a global depression measure. Cut-points were related to limitations in physical function, suggesting differences in the quality of patients' lives. The resulting cut-points summarize severity ratings into clinically significant and useful categories that clinicians can use to assess symptoms in their practices.

Stimulating the development of mechanism-based, individualized pain therapies

Biomedical science has greatly improved our understanding of pain in recent decades, but few novel molecular entities that address fundamentally new pain mechanisms have entered the clinic, despite dramatically increased pharmaceutical investment. Indeed, virtually all new analgesics approved over the past 25 years are derivatives or reformulations of opioids or aspirin-like drugs, existing drugs given for a new indication or older drugs given by a different route of administration. Here, we discuss factors contributing to this lack of innovation in therapies for pain and advocate public-private partnerships (PPPs) to translate new knowledge into more efficacious and safer treatments.

Trial of a new pain assessment tool in patients with low education: the full cup test

AIMS AND SCOPE

Pain is subjective and pain assessment depends on the patient's self-report. The measurement of pain needs simple tools, especially in patients with low education. There are limited reports about pain assessment in this type of patient. The aims of the present study were to develop a pain scale that is easy for patients with low education to understand and to evaluate its usefulness in these patients.

METHODS

A total of 128 adult non-demented patients presenting with headaches or rheumatologic pain were included in this study. The first phase of the study involved 114 patients and aimed to estimate the usefulness of the full cup test (FCT) compared with the visual analogue scale (VAS). The second phase of the study involved 23 patients with headaches selected randomly from the 114 patients and assessed the usefulness of the FCT for detecting changes in pain levels. The third phase of the study involved 14 patients with low education suffering from headaches and examined the usefulness of the FCT in these patients.

RESULTS

The mean VAS and FCT scores were statistically correlated and reliable and did not differ significantly. Patients with low education understood the FCT more easily than the VAS.

CONCLUSION

We concluded that the FCT is useful for both assessing and differentiating changes in pain, and is suitable for assessing pain in patients with low education.

Maternal separation leads to persistent reductions in pain sensitivity in female rats

We determined responses to noxious thermal stimuli, before and after morphine, and mu-opioid receptor binding in brain regions involved in nociception in maternally separated (MS), neonatally handled (H) and nonhandled (NH) female rats. Long-Evans dams were randomly assigned to either 180-minute (MS) or 15-minute (H) minute daily separations from their litters or left undisturbed (NH). At 120 days of age, paw lick latency (50 degrees C hot plate) was determined in offspring during diestrous. Rats were then given 1, 2, 5, or 10 mg/kg morphine and paw lick latency was measured. Rats were killed during diestrous and mu-opioid receptor binding was determined in discrete brain regions, using [(3)H]DAMGO autoradiography. MS rats had significantly longer (P < .05) paw lick latencies compared with H rats. The percent maximal possible effect of morphine was significantly (P < .05) lower in MS compared with H rats for the 5 mg/kg dose. Mu-Opioid receptor binding capacity was significantly greater (P < .05) in MS rats compared with H rats in the medial preoptic nucleus. In conclusion, MS and H treatments led to antipodal differences in pain sensitivity in female rats and differential mu-opioid receptor binding in the medial preoptic nucleus.

PERSPECTIVE

This article describes the persistent impact of early life adversity on pain sensitivity and the analgesic potency of morphine. Clinically, early life history may play an important role in pain symptoms and responses to opioid analgesics.

The use of a responder analysis to identify differences in patient outcomes following a self-care intervention to improve cancer pain management

Previously, we demonstrated, in a randomized clinical trial, the effectiveness of a psychoeducational intervention to decrease pain intensity scores and increase patients' knowledge of cancer pain management with a sample of oncology patients with pain from bone metastasis. In the present study, we evaluated for changes in mood states (measured using the Profile of Mood States), quality of life (QOL; measured using the Medical Outcomes Study Short Form-36 (SF-36)), and pain's level of interference with function (measured using the Brief Pain Inventory (BPI)) from baseline to the end of the intervention first between the intervention and the standard care groups and then within the intervention group based on the patients' level of response to the intervention (i.e., patients were classified as non-responders, partial responders, or responders). No differences were found in any of these outcome measures between patients in the standard care and intervention groups. However, when patients in the intervention group were categorized using a responder analysis approach, significant differences in the various outcome measures were found among the three respondent groups. Differences in the physical and mental component summary scores on the SF-36 and the interference items on the BPI, among the three respondent groups, were not only statistically significant but also clinically significant. The use of responder analysis in analgesic trials may help to identify unique subgroups of patients and lead to the development of more effective psychoeducational interventions.

Revisiting sugar-fat mixtures: sweetness and creaminess vary with phenotypic markers of oral sensation

Genetic variation in oral sensation presumably influences ingestive behaviors through sensations arising from foods and beverages. Here, we investigated the influence of taste phenotype [6-n-propylthiouracil (PROP) bitterness, fungiform papillae (FP) density] on sweet and creamy sensations from sugar/fat mixtures. Seventy-nine subjects (43 males) reported the sweetness and creaminess of water or milk (skim, whole, heavy cream) varying in sucrose (0-20% w/v) on the general Labeled Magnitude Scale. Sweetness grew with sucrose concentration and when shifting from water to milk mixtures--the growth was greatest for those tasting PROP as most bitter. At higher sucrose levels, increasing fat blunted the PROP-sweet relationship, whereas at lower levels, the relationship was effectively eliminated. Perceived sweetness of the mixture exceeded that predicted from the sum of components at low sucrose concentrations (especially for those tasting PROP most bitter) but fell below predicted at high concentrations, irrespective of fat level. Creaminess increased greatly with fat level and somewhat with sucrose. Those tasting PROP most bitter perceived greater creaminess in the heavy cream across all sucrose levels. Perceived creaminess was somewhat lower than predicted, irrespective of PROP bitterness. The FP density generally showed similar effects as PROP on sweetness and creaminess, (but to a lesser degree) and revealed potential taste-somatosensory interactions in weakly sweet stimuli. These data support that taste phenotype affects the nature of enhancement or suppression of sweetness and creaminess in liquid fat/sugar mixtures. Taste phenotype effects on sweetness and creaminess likely involve differential taste, retronasal olfactory, and somatosensory contributions to these perceptual experiences.

Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives

Psychophysical comparisons seem to show that obese individuals experience normal sweet and fat sensations, they like sweetness the same or less, but like fat more than the non-obese do. These psychophysical comparisons have been made using scales (visual analogue or category) that assume intensity labels (e.g. extremely) which denote the same absolute perceived intensity to all. In reality, the perceived intensities denoted by labels vary because they depend on experiences with the substances to be judged. This variation makes comparisons invalid. Valid comparisons can be made by asking the subjects to rate their sensory/hedonic experiences in contexts that are not related to the specific experiences of interest. Using this methodology, we present the evidence that the sensory and hedonic properties of sweet and fat vary with body mass index. The obese live in different orosensory and orohedonic worlds than do the non-obese; the obese experience reduced sweetness, which probably intensifies fat sensations, and the obese like both sweet and fat more than the non-obese do. Genetic variation as well as taste pathology contribute to these results. These psychophysical advances will impact experimental as well as clinical studies of obesity and other eating disorders.

Rational multidrug therapy in the treatment of neuropathic pain

Multidrug therapy (MDT) has been widely accepted and used as a standard of practice in most areas of medical practice, including neuropathic pain. Because neuropathic pain is a new field of medical science and practice, standards for its treatment including MDT are still evolving. In this article, we present rationale and principals for the MDT of neuropathic pain based on our best understandings of the underlying mechanisms of the disease processes and the actions of drugs, the goal being to maximize benefits and minimize adverse effects. MDT for neuropathic pain is based on a comprehensive clinical neuropathic pain assessment and ongoing monitoring of the drug therapy's efficacy and adverse effects, administering one drug at the time.

Individual differences in pain responses

The experience of pain is characterized by tremendous inter-individual variability. Indeed, an identical noxious stimulus can produce vastly different pain responses across individuals. Historically, scientists have regarded this variability as a nuisance; however, substantial data suggest that these individual differences may provide valuable information that can be used to enhance clinical management of pain. This paper discusses several factors that contribute to individual differences in pain perception, including demographic (ie, sex, age, and ethnicity), genetic, and psychosocial variables. These factors are discussed in the context of the biopsychosocial model of pain, which posits that pain perception is influenced by interactions among biologic, psychosocial, and sociocultural factors. Finally, the clinical and scientific implications of individual differences in pain are discussed.