How many dimensions are needed to describe pain properly? Accepted for publication 7 March 2015 doi:10.1002/ejp.706

€ffler, M., Flor, H. and Anton, F. This commentary accompanies the following article: Bustan, S., Gonzalez-Roldan, A.M., Kamping, S., Brunner, M., Lo (2015), Suffering as an independent component of the experience of pain. Eur J Pain 19, 1035-1048.

The International Association for the Study of Pain has defined pain as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’. We all know this definition clearly pointing out two different dimensions of pain. But can we describe the whole pain experience with only two dimensions or do we need more? In this issue of the European Journal of Pain you will find the following article by Bustan et al. (2015) entitled: The authors tried to give an answer to this old question and assess the value of a third dimension. They evaluated pain-related suffering in addition to the classical pain assessment relying on intensity and unpleasantness as measures of the sensory-discriminative and motivational-affective pain components. In their sample of healthy volunteers, they showed that suffering constitutes an integral component of pain processing that is distinct from intensity and unpleasantness. In addition, they showed that tonic, rather than phasic stimulations, were eliciting more pain and suffering. The findings of this study are potentially important since they point out that the simple two-dimensional evaluation does not incorporate the whole experience of pain. According to the authors, the addition of a third visual analogue scale (VAS) to quantify pain-related suffering seems to be a simple way to better characterize this experience, at least in healthy volunteers.

2. An old idea renewed In 1968, Melzack and Casey were already describing three dimensions of pain: sensory-discriminative, affective-evaluative and cognitive-evaluative (Melzack and Casey, 1968). Several other groups have studied multidimensional scaling of various innocuous or painful conditions (cancer pain, electrical or thermal stimuli) (Clark et al., 1986, 1989;

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Janal et al., 1991). Two dimensions emerged consistently and it was proposed to use pain intensity as a measure of its sensory-discriminative aspect and unpleasantness as a measure of its motivationalaffective aspect. Several other rating parameters were sometimes described, notably a third one referring to pain being ‘unbearable’, ‘excruciating’ and ‘threatening’. The corresponding ‘third dimension’ was found unreliable and ambiguous in the context of multidimensional scaling, leading to focus on what has since become the traditional two-dimensional assessment configuration. Nonetheless, every pain specialist evaluates patients’ pain with more than 2 VAS scores. Indeed, the interlink between pain and anxiety, depression, quality of life, impaired sleep or impaired cognitive function is well-known. In a perfect world, one could assess all these parameters, using for example the short form of the Mc Gill pain questionnaire (Melzack, 1987), the Brief Pain Inventory (Cleeland and Ryan, 1994), the SF-36 (Ware and Sherbourne, 1992), the hospital anxiety and depression scale (Zigmond and Snaith, 1983), the MOS sleep scale (Allen et al., 2009) and a neuropsychological assessment. But for the clinician, a real multidimensional evaluation of pain and pain consequences can be too much time-consuming. This multiplication of scales can only be done for research purposes but is hardly feasible in daily practice. Thus, evaluating the three principal components of pain experience could be an appropriate first step, even if it is imperfect. However, as seen in many studies in the past, only two parameters seem very robust in all painful conditions. And this is probably the most important point! If the third dimension was constant and reliable in various experimental and clinical conditions, it would have probably been described and used for years. Though, it is absolutely necessary to confirm the results of the present study in various samples of

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patients, both in acute or chronic pain conditions to see if this third dimension, surely gathering a multitude of subdimensions, is still an independent factor to better evaluate the pain experience.

3. Conclusion The multidimensional evaluation of pain is obviously necessary. As time is limited in everyday practice, the introduction of a new tool for a simple and fast evaluation of the multidimensional aspects of pain would be a good point. The addition of a third dimension to roughly evaluate pain suffering is an idea. This third dimension, easily evaluated via a VAS could be a first step towards more precise description of the factors influencing this suffering rating. However, the pertinence of this third component is questionable and it is necessary to validate its independence and reliability in patients. X. Moisset1,2,3,, D. Bouhassira1,4 Inserm U-987, Centre d’Evaluation et de Traitement de la Douleur, CHU Ambroise Par e, Assistance Publique H^ opitaux de Paris, Paris, France 2 Inserm U-1107, Clermont Universit e, Universit e d’Auvergne, Clermont-Ferrand, France 3 CHU Gabriel Montpied, Service de Neurologie, Clermont Universit e, Universit e d’Auvergne, Clermont-Ferrand, France 4 Universit e Versailles-Saint-Quentin, Versailles, France 1

Conflicts of interest None declared. References Allen, R.P., Kosinski, M., Hill-Zabala, C.E., Calloway, M.O. (2009). Psychometric evaluation and tests of validity of the Medical Outcomes Study 12-item Sleep Scale (MOS sleep). Sleep Med 10, 531–539. Bustan, S., Gonzalez-Roldan, A.M., Kamping, S., Brunner, M., Loeffler, M., Flor, H., Anton, F. (2015). Suffering as an independent component of the experience of pain. Eur J Pain 19, 1035–1048. Clark, W.C., Carroll, J.D., Yang, J.C., Janal, M.N. (1986). Multidimensional scaling reveals two dimensions of thermal pain. J Exp Psychol Hum Percept Perform 12, 103–107. Clark, W.C., Ferrer-Brechner, T., Janal, M.N., Carroll, J.D., Yang, J.C. (1989). The dimensions of pain: A multidimensional scaling comparison of cancer patients and healthy volunteers. Pain 37, 23–32. Cleeland, C.S., Ryan, K.M. (1994). Pain assessment: Global use of the Brief Pain Inventory. Ann Acad Med Singapore 23, 129–138. Janal, M.N., Clark, W.C., Carroll, J.D. (1991). Multidimensional scaling of painful and innocuous electrocutaneous stimuli: Reliability and individual differences. Percept Psychophys 50, 108–116. Melzack, R. (1987). The short-form McGill Pain Questionnaire. Pain 30, 191–197. Melzack, R., Casey, K (1968). Sensory, motivational, and central control determinants of pain: A new conceptual model. In The Skin Senses, D.R. Kenshalo, ed. (Springfield, IL: Thomas) pp. 423–443. Ware, J.E., Sherbourne, C.D. (1992). The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 30, 473–483. Zigmond, A.S., Snaith, R.P. (1983). The hospital anxiety and depression scale. Acta Psychiatr Scand 67, 361–370.

Correspondence Xavier Moisset E-mail: [email protected]

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How many dimensions are needed to describe pain properly?

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