MPQ CLASSIC (C.J.Main) Supplementary Tables

MPQ CLASSIC (C.J.Main) Supplementary Tables

Table S1

A brief history of pain* prior to the GCT

In antiquity, pain,often in conjunction with suffering, was attributed to the will of the gods. There was some interest in the location, timing and prognostic value of pain, but both aetiology and treatment were framed in terms of the influence of the four humours and the need for balance amongst the pairs of opposites.

Bythe early 16th century, pain was being attributed to the wrath of God, with man a sinner saved only by the doctrine of grace. The classical age is characterised by the growth of science with the rejection of occultism.

The origins of the later specificity theory Von Frey (1922) can be found in the writings of Descartes et al (1664). and his well-known depiction of pain pathways (consisting of hollow neural tubes which serves as conduits for “animal spirits” which transmitted information on stimulus characteristics such as intensity and quality from the peripheral pain site to the pineal gland). However, according to Moayadi & Davis (2013), his depiction of the modality specific pathways (e.g. for pain and touch) may have been based on his understanding of how visual images registered in the brain. He postulated two sorts of nerves of feeling in skin and the experience of pain was taken to confirm the existence not only of the body but of external bodies and senses. However this knowledge allowed us only to become acquainted with what was useful or noxious but never with the precise nature of pain.

It was only through the order of succession of sensations that we could determine whether the origin of the pain was external or internal. His ideas of the origins of pain were interesting not only from an epistemological point of view, but also in terms of the perception of pain, and his concept of variations in sensations and the crossing of thresholds into a painful sensation and allowing the internal life to reach consciousness has some resonance with the later summation theory (discussed below)

By the beginning of the 18th Century, the problem of pain come had become progressively disentangled from ideas of sin, evil, and punishment. Interest developed in the nature and measurement of physiological sensibility and its possible relevance to the etiology of disease. Pain came to be seen as a warning signal and as having a preventative role. There was still fierce debate however about the nature and function of pain.

According to Rey (1995), a number of different types of pain began to be distinguished, with an attempt tried to align types of pain with types of illness. However communalities were also recognised and pain was also viewed as a quasi-universal symptom of all illness. Interest became focused not only on physical signs but also on physical symptoms, and this brought the nature of doctor-patient communication into clear focus. While this move towards more patient-centred communication might be viewed as an encouraging development, the search for “objectivity” also had its downside, and when the symptoms did not seem to map adequately onto the physical signs which were elicited, this could be viewed as suspicious. According to Rey (1995) “there was hardly a more difficult or controversial problem to solve than that of knowing what value to place on a patient’s complaints”, p101. Issues of veracity and possible exaggeration in people with pain are still evident today, and the legitimacy of pain has been at the heart of the conservative-liberaldebate central in the politics of pain in the USA (Wailoo, 2014), and featured strongly in Personal Injury litigation nin the U.K (Main, 2003)..

By the middle of the18th Century, advances in science stimulated investigations into human physiology which required reconsideration of the nature and significance of pain and suffering as facets of the human constitution, although the focus diverged sharply from the Aristotelian perspective on pain as an emotion The modern broad conceptualisation of pain as a biopsychosocial phenomenon, (Engel,1977; Waddell,1987, Gatchel et al,2007) however had still not emerged and developments over the next two centuries were dominated by physiology and anatomy with a focus primarily on the elucidation of pain pathways, and transmission of information in the peripheral and central nervous system. “Pleasure-pain” theorists such as Marshall (1895) re-awakened interest in the relationship between pain and emotion and Strong (1895) advocated a distinction between the original sensation of pain, and the psychological reaction to it, a distinction later adopted by Sherrington (1900) in his influential article on cutaneous sensation.

Principal pain theories

The most influential theories on current concepts of pain prior to the GCT have been the Specificity (or Labeled Line) theory, the Intensity (or Summation) theory and the Pattern theory, although there have been also a number of derivatives (Moayadi & Davis,2013).

The specificity theory postulated specific anatomical receptors, each responsive to a specific stimulus (such as touch or pain) which were transmitted ultimately to a specific region of the brain along distinct pathways. Its principal proponent was von Frey (1922), although, as previously discussed, its origins can be found in Descartes. In any event, according to Dallenbach (1939), later developments in physiology, such as the discovery by Goldscheider (1881) and Blix (1884) of sensory spots in the skin specific to warmth, cold, pressure and pain seemed to support the notion of specific receptors, although in a later elaboration the different sensations were attributed not to the receptors but to differing projection of the transmitting nerve fibres (Goldscheider,1920) and von Frey’s experimental studies identified receptors responsive to different intensities of pressure.

The intensity (or summation) theory (Dallenbach,1939; Goldschneider,1920) postulated low- and high- threshold stimuli , so that whether or not a stimulus was perceived as painful depended not on stimulation of a particular pathway, but on whether the extent of the neural stimulation reached a threshold, thereby stimulating second-order neurons in the dorsal horn. Livingston (1943), in support of the intensity theory, put forward the idea of central summation in which prolonged abnormal activity bombarded the spinal transmission (T) cells which projected up to the brain and resulted in the perception of pain.

The peripheral pattern theory (Nafe,1929; Sinclair,1965; Weddell,1955; Livingston,1943)emphasised patterns of neural firing whereby barrages of impulses produced in different sensory fibers initiated a computation in the central nervous system that was decoded into a somesthetic experience based in part on other ongoing brain activity. The important departure from the specificity theory was that the fibres were not viewed as having specific responsibilities for a particular sensory modality such as heat or touch. Mendell (2014) and Bonica & Loeser (2011) also make specific mention of the sensory interaction theory (Noordenbos (1959) which can be viewed as a refinement of the intensity theory.This put forward the key distinction between myelinated and unmyelinated fibres (anticipating different roles in the fast and slow transmission of nerve impulses).

A contemporary view(1977)of pain mechanisms

According to Mendall (2014), Melzack’s early animal research into the reaction to pain and subsequent avoidance had led him to suspect that the response to pain could not be explained simply on the basis of the frequency/intensity of stimulation or on reflex

responses alone, but required consideration of previous experience. Further research with Wall on pain processing (Melzack & Wall,1962) had not fully supported either the specificity or the intensity theories, but had established that the “psychological dimension of the somesthetic experience could not be fully explained from the activity of differences in specific skin receptor types”.

How things looked at the time of the MPQ can be gleaned from a contemporary account (Dennis and Melzack, 1977) which outlined the lateral and medial ascending systems thought to transmit nociceptive information from the spinal cord to the brain.The “lateral” group though similar in function, differedinthe precise modes ofterminationandroutes ofascension and appeared to be controlled differently by the inhibitorysystems descending from the brain. The "medial"group, appeared to havethe samemodalityspectrum, but they differed from the lateral group inconductingmoreslowly; their cell bodies tended to belocated more deeply inthe spinal greymatter;and,most importantly,their patternsof termination weregrossly differentfrom those of the lateral group. In attempting to explain interactions among the pathways and differences in function they considered two main factors: (1)thepossibleinfluenceofon-going behavioral sequenceson the relative activity among thesystems; and(2)the possible effects of existing tissue damage on themediation ofsubsequent noxious stimuli.

Pain signalling pathways and influences on them

They stated that in addition to the major pain tracts in the ventral cord, there are small, functional pain-signalling pathwaysin the dorsal cord .For example, under the Melzack-Casey conceptualization (Melzack & Casey,1968),the fast, direct systemsmediatesensory-discriminativeand centralcontrol triggering functions, while the medial systemsmediatethe affective-motivational dimensionof pain. They opined further that pain-signalling processes may vary accordingto the organism'sbehavior and behavioral state.On the one hand, proprioceptiveand tactile stimuli occurringduring particular behavioral patternsmight havespecific inhibitoryeffects onpaintransmission.On the otherhand, it ispossible that, concomitant with the behavioral patterns themselves and the motorcommandsthat producethem, differentialeffects were exerteddirectly on the multiple pain-signalling systemsto change the relativeactivity among them. Thiscould alter not only the perceived intensity of noxiousstimulation,but also the form of the organism'sreactionto it. Thus, the individual's environment and psychological history,both ofwhich areantecedentsof behavior, might inpart controlthephysiological mechanismswhich mediate pain, perhaps even at the levelof the first synapse.

Conclusion

The core advance in theory underpinning the GCT was that pain was evoked when brain activity reached a certain level as a result of sensory and/or central inputs (Mendell,2014)(my italics). This paved the way for the integration of physical and psychological factors in pain perception, crystallised in the concept of the neuromatrix (Melzack,1990, Melzack,2005)and opened the door for research specifically into the nature and influence of psychological factorson pain perception and the response to pain, an aspect of which was the identification and interpretation of the way in which people describe and report their experience of pain.

*Acknowledgement

In preparation of this brief precis, I have relied in particular to Rey’s textbook (1995)and the reviews by Bonica & Loser (2011); Moayedi & Davis (2013); and Mendell,(2014)

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TableS2

General description of the MPQ, the SF-MPQ and the SF-MPQ2

MPQ (Melzack,1975)

The original McGill Pain Questionnaire (MPQ), sometimes described as the LF-MPQ or long-form MPQ, is illustrated in Figure 1a. It comprises a list of 78 words grouped into twenty classes of adjective, grouped in turn into one of four categories (Sensory, Affective, Evaluative and Miscellaneous) yielding a set of scale scores.

The Pain Rating Index (PRI) is based on the rank value of the preferred word in

each of the 20 sub-classes. The rank values are summed across sub-classes 1-10 to give a Sensory score (PRI-S); summed across sub-classes 11- 15 to give an Affective score (PRI-A); a single Evaluative score (PRI-E) from sub-class 16, and a miscellaneous score (PRI-M), summed across sub-classes 17-20). The PRI-T, is the total score obtained from all 20 classes.

A fifth score obtained from the pain descriptors is the NWC or the number of words chosen, irrespective of their scale value.

Finally, the Present Pain Intensity (PPI) is obtained from an additional overall rating on a six-point scale of the current pain at the time of administration.

In addition to the six scores, there is a body diagram (front and back) on which the location of pain can be depicted the sites categorised as external (E) or internal (I) and an indication of temporal features can be obtained from the endorsement of nine words grouped into three sets. The layout is shown in Figure 1a

Figure 1a about here

Variants in format

In an early meta-analysis five different variants of the MPQ were identified with differences in content, layout and format options (Wilkie et al, 1990, p37, Table 1).

Common features were the incorporation of pain descriptors, the overall 6-point rating of pain intensity and use of a body outline. However there were differences among the studies in administrative procedure and in the inclusion of additional clinical descriptors, with 60% of the studies either not reporting the version used or modifying it in some way make comparisons problematic. When the MPQs were compared across seven different pain conditions by constructed grand weighted mean scores and adopting specific criteria in data reporting, chronic conditions were differentiated from acute conditions primarily by higher affective scores and of the 78 quality descriptors, only 19 were selected by >20% of the participants (Wilkie et al,1990a).

Studies have usually adopted the original MPQ scoring system but empirically derived groupings based on similarity of choices have also been proposed (Yerkes et al, 1989)

The Short-Form MPQ (SF-MPQ) (Melzack,1987)

Accordingly to Melzack (1987), a shortened version of the MPQ was desirable for some typesof research (such as pharmacological studies) requiring more rapid acquisition ofdata.He therefore selected the most commonly used sensory and affective descriptors in all the clinical studies he had performed up to that time (Melzack,2005) to constitutea “small, representative set of words from the sensory and affective categories of the standard form which had been endorsed by at least 33% of patients with a range of pain conditions (Melzack,1987), but he added “splitting” since it was reported to be a key discriminative work for dental pain. The resulting main component of the SF-MPQ consists of 15 descriptors (11 sensory; 4 affective) which are rated on an intensity scale as 0 = none, 1 = mild, 2 = moderate or 3 = severe. Three pain scores are derived from the sum of the intensity rank values of the words chosen for sensory, affective and total descriptors. The PPI from the original MPQ and a visual analogue scale (VAS) of overall intensity were also added.Preliminary cross-comparisons with the original MPQ were also undertaken and the correlations were reported to be “consistently high and significant” and the SF-MPQ was similarly sensitive to treatment as the original.

The layout is shown in Figure 1b.

Figure 1bThe SF-MPQ (Melzack, 1987)

The revised Short-Form (SF-MPQ-2) (Dworkin et al,2009)

The SF-MPQ-2 was developed in response to a perceived need to expand the number of sensory descriptors characteristic of neurogenic pain (Dworkin et al,2009).The stated intent was to develop a single measure of the major symptoms of both neuropathic and non-neuropathic pain that could be used in studies of epidemiology, natural history, pathophysiologic mechanisms, and treatment response. The authors state explicitly however that the objective was not designed to produce another neuropathic pain scale but rather “to revise the SF-MPQ so that it would provide a comprehensive assessment and characterization of the symptoms of both neuropathic and non-neuropathic pain”, p 40. They state further that they compared the responses of individuals with self-reported neuropathic and non-neuropathic pain “solely to identify new items relevant to the assessment of neuropathic pain, not to evaluate group differences that would provide a basis for selecting items that could be used in screening for neuropathic pain.

A preliminary list of 24 items was included in a large web-based survey (Turk et al, 2008) of people with painful conditions and the particapants were then classified as having neuropathic or non-neuropathic pain. Further clinmetric data was obtained from a sample of patients participating in an RCT of post-diabetic neuropathy and the final list of items was reduced to 22. Seven additional descriptors were added to the 15 in the SF-MPQ, the word pain was added to a number of the descriptors, the response format was changed to a 0–10 numerical rating scale to provide increased responsiveness in longitudinal studies and clinical trials, and the instructions for rating were made slightly more explicit. It is shown in Figure 1c