The individual feeling of suffering and the personal translation of that experience into a patient’s daily living is the signature of the heterogenous subjectivity of chronic pain. By definition, a painful experience is always a personal interpretation. Yet, despite this knowledge, clinicians, pain physicians and clinical researchers still often use oversimplifications and minimizations of a patient’s health status through unidimensional constructs such as pain intensity.
Pain intensity can be reported in various ways such as written, visual or verbal reportings. The most frequently used scales in chronic pain settings to measure pain intensity are the Numerical Rating Scale (NRS), the Visual Analogue Scale (VAS), the Verbal Rating Scale (VRS), and the Faces Pain Scale-Revised (FPS-R)1,2. The two most popular scales are the VAS and NRS, whereby the NRS (an 11-point scale ranging from 0 (“no pain”) to 10 (“worst pain imaginable”)) is sometimes mistaken for a VAS (100 mm scale on a 10 cm line) and vice versa3. Additionally, scores from one scale are sometimes converted to another pain intensity scale, especially in the context of meta-analyses4,5. Yet, the ongoing ICD-11 guidelines consider NRS and VAS as separate measurement instruments, each with their own cut-off values to code pain severity6. Within a chronic pain setting, a study in 366 patients with chronic pain revealed that VAS and NRS scores are not in agreement with each other, despite the fact that one-dimensionality has been proven for both pain measures7. This means that the disagreement between NRS and VAS scores could not be explained by measuring different information with both scales. The disagreement between two pain intensity scores that are widely implemented in both clinical research and clinical practice, seriously questions the value of pain intensity scores as gold standard outcome variable in chronic pain settings and limits the translation of scores on one scale towards another8.
In line with the broad impact of chronic pain on daily patient functioning, a less narrow evaluation is proposed by measuring a combination of concepts such as pain interference, functioning, health-related quality of life, medication usage, patient satisfaction, etc. These findings could be combined in a composite score to serve as outcome measure to evaluate chronic pain9,10. Composite scores can combine several constructs into one overall measure thereby providing a more comprehensive assessment and presumably a more clinically relevant measure of multiple domains compared to a single pain intensity score10. The use of composite measures drastically increased during the last years to provide a more in-depth evaluation of the broad impact of pain on individual patients. Presumably, the search towards reliable and valid biomarkers for pain will also reveal this shift and will focus on finding biomarkers for composite measures of pain.
Nevertheless, one could question the value of pain intensity scores and composite scores in light of precision pain medicine. This concept focuses on employing methods to assess each patient individually, identify the risk profile of individual patients for the presence of disproportionate pain and/or the development of chronic pain, and optimize treatment to target specific pathological processes underlying chronic pain11. Perhaps the use of composite measures consisting of self-reported (subjective) measures is a first step towards precision pain medicine, but still an oversimplification.
Lisa Goudman
FWO junior postdoctoral researcher and assistant Professor at STIMULUS research group, VUB.
2024Pain in Motion
References and further reading:
1. Euasobhon P, Atisook R, Bumrungchatudom K, Zinboonyahgoon N, Saisavoey N, Jensen MP. Reliability and responsivity of pain intensity scales in individuals with chronic pain. Pain 2022; 163(12): e1184-e91.
2. Thong ISK, Jensen MP, Miro J, Tan G. The validity of pain intensity measures: what do the NRS, VAS, VRS, and FPS-R measure? Scandinavian journal of pain 2018; 18(1): 99-107.
3. Bielewicz J, Daniluk B, Kamieniak P. VAS and NRS, Same or Different? Are Visual Analog Scale Values and Numerical Rating Scale Equally Viable Tools for Assessing Patients after Microdiscectomy? Pain Res Manag 2022; 2022: 5337483.
4. Hjermstad MJ, Fayers PM, Haugen DF, et al. Studies comparing Numerical Rating Scales, Verbal Rating Scales, and Visual Analogue Scales for assessment of pain intensity in adults: a systematic literature review. J Pain Symptom Manage 2011; 41(6): 1073-93.
5. Choi HY, Lee CH. Can Beta-Endorphin Be Used as a Biomarker for Chronic Low Back Pain? A Meta-analysis of Randomized Controlled Trials. Pain medicine (Malden, Mass) 2019; 20(1): 28-36.
6. Treede RD, Rief W, Barke A, et al. Chronic pain as a symptom or a disease: the IASP Classification of Chronic Pain for the International Classification of Diseases (ICD-11). Pain 2019; 160(1): 19-27.
7. Goudman L, Pilitsis JG, Billet B, et al. The level of agreement between the numerical rating scale and visual analogue scale for assessing pain intensity in adults with chronic pain. Anaesthesia 2023.
8. Jensen MP, Miró J, Euasobhon P. Assessing pain intensity: critical questions for researchers and clinicians. Anaesthesia 2024; 79(2): 114-8.
9. Patel KV, Allen R, Burke L, et al. Evaluation of composite responder outcomes of pain intensity and physical function in neuropathic pain clinical trials: an ACTTION individual patient data analysis. Pain 2018; 159(11): 2245-54.
10. Gewandter JS, McDermott MP, Evans S, et al. Composite outcomes for pain clinical trials: considerations for design and interpretation. Pain 2021; 162(7): 1899-905.
11. Chadwick A, Frazier A, Khan TW, Young E. Understanding the Psychological, Physiological, and Genetic Factors Affecting Precision Pain Medicine: A Narrative Review. Journal of pain research 2021; 14: 3145-61.
