DEVELOPING A COMPARATIVE SCALE OF DIFFERENT NOCICEPTIVE AND NEUROPATHIC PAIN THROUGH TWO PSYCHOPHYSICAL METHODS

O objetivo geral foi escalonar os diferentes tipos de dor existentes, comparativamente entre si, sendo investigados por meio de diferentes métodos psicofísicos. Os métodos psicofísicos utilizados foram o método de estimação de magnitudes e o de estimação de categorias. Participaram 30 pacientes ambulatoriais de diferentes clínicas, 30 médicos e 30 enfermeiros. Os resultados mostraram que a dor no câncer, dor por infarto do miocárdio, a dor por cólica renal, dor por queimadura e a dor no parto foram consideradas os tipos de dor de maior intensidade, independente do método psicofísico utilizado ou da amostra estudada. As ordenações de posições da intensidade dos diferentes tipos de dor, comparando os diferentes métodos psicofísicos utilizados, resultaram em níveis de concordância significativa com valores de Kendal próximos de 1,00. Houve divergências na percepção das intensidades de alguns tipos de dor, essas divergências foram observadas principalmente entre profissionais e pacientes.


INTRODUCTION
Health professionals' main function is to alleviate pain and suffering.For that, they need to get rid of beliefs, preconceptions and previous individual experiences, and understand the patient with pain in his(er) totality as a unique being with particular characteristics.
In addition to understanding someone's pain, it is also important to understand the person per se, what this person perceives and feels and how (s)he deals with these feelings (1)   .
Pain is composed of two elements: "the original sensation and the reaction to this sensation", that is, response to a painful sensation depends on a series of individual intrinsic and extrinsic aspects.Thus, measuring a painful sensation is a complex task (2) .
The history of pain measurement was analyzed and three branches of activity were identified, which are: psychophysics, multidimensional questionnaires using standardized descriptors and intensity scales (3) .The authors report that such historical concern arises from the need to establish reliable, valid and sensitive measures to define the efficacy of analgesics and other therapies.
There are some studies in the psychophysics area focusing on pain perception, which use experimental pain induction in different samples, aiming to compare "reactions to sensations".
Psychophysics defines the threshold and tolerance to pain by inducing experimental pain and comparing ethnical groups, genders at different ages and different life habits, among others variables (4)(5) .
In addition, the psychophysical method can be used in studies on clinical pain that results from pathological conditions.The psychophysical law is also known as Stevens' power law.It is related to the psychological magnitude and physical intensity of a stimulus and can be described by a power function, which relates stimulus and subjective response in a curve (6)(7) .
This function describes a situation in which a geometric increase in physical magnitude corresponds to a geometric increase on the subjective or psychological scale.Its exponent reflects a relative rate of increase between the two scales and, thus, the principle that equal ratios between stimuli produce equal ratios between responses (7) .
In the magnitude estimation method, elaborated by Stevens' Modern Psychophysics, individuals select and use a range of numbers that represent their subjective amplitude.Opposed to this method is the category estimation method, in which the experimenter arbitrarily chooses the amplitude of categories (6)(7) .
This method has important characteristics, such as the strategy to measure subjective concepts like pain.Some of these characteristics are: the production of scales as ratios increases the sensitivity of measurement; resulting scales and judgments are reproducible, stable, with records of test and re-test and reliability coefficients close to 0.908; the test is cost-efficient because there is no loss of data and data can be individually or collectively collected (6)(7)(8) .
The psychophysical method is used in this study to improve the knowledge on this subjective and perceptual phenomenon.

OBJECTIVE
Developing a comparative scale of different pain types through different psychophysical methods.In the second method, the participants' task was to score from one to seven, each different type of pain based on the perceived intensity of pain.

PAIN MEASUREMENT
Participants were asked to assign the maximum For the magnitude estimates, geometric averages and standard deviations of geometric averages for each type of pain were computed.For the category estimates, average and standard deviations were also calculated for each type of pain.
In addition, Kruskal-Wallis' non-parametric test and Mann-Whitney's test were computed to compare pain intensities between samples.Kendall's W was computed to compare concordance between the used methods.

RESULTS
The results presented in Tables 1 and 2 correspond to the scaling of different pain types in decrescent order, that is, from the pain considered of highest intensity to the one considered of lowest intensity.The scaling is presented according to t h r e e s t u d i e d s a m p l e s : o u t p a t i e n t s ' g r o u p , physicians' groups and nurses' group.Scaling was performed through two measurement methods: m a g n i t u d e e s t i m a t e s ( Ta b l e 1 ) a n d c a t e g o r y estimates (Table 2).
The types of pain the outpatients considered of highest intensity, both in the magnitude estimation and category estimation methods, were cancer pain, renal colic, myocardial infarction pain and pain in AIDS.The types of pain considered of highest intensity by the physician and nursing groups were equivalent.They were: cancer pain, renal colic, labor pain, myocardial infarction pain and burn-injury pain (Tables 1 and 2).
It is worth mentioning that cancer pain was considered by the three samples as one of the most intense pain types in the two methods used (magnitude estimation and category estimation) and was considered the most intense in the outpatients' and nurses' groups and the second most intense in the physicians' group.
The types of pain considered of lowest intensity by the outpatient group, both in the magnitude estimation and in the category estimation methods, were pain by repetitive motion disorder, pain in TMJ disorder, low back pain and headache; for the physicians' group, they were repetitive motion disorder pain, joint pain, fibromyalgia, low back pain and menstrual colic; and for the nurses' group, they were menstrual colic, low back pain, repetitive motion disorder pain, pain in TMJ disorder and tooth pain.
Kruskal-Wallis' non-parametric test was used for each type of pain, comparing the studied samples in each of the methods used.When the difference between samples was statistically significant, with p<0.05,Mann-Whitney's paired test was used to compare pain scores between samples (patientsphysicians; patients-nurses; nurses-physicians).
Tables 1 and 2 show the p-values for each type of pain.Next, the types of pain that presented scores with statistically significant differences between the studied samples are presented.
Table 1 -Geometric average of magnitude estimates (ME) for the different types of pain by ranking (R) according to outpatients, physicians and nurses HCFMRP/USP, 2007 1-Pain in AIDS -statistically significant differences between patients-physicians and between patients-nurses, p<0.017.2-Myocardial infarction pain -statistically significant differences between patients-nurses, p<0.017.
3-Biliary colic -statistically significant differences between patients-nurses, p<0.017.4-Fibromyalgia -statistically significant differences between patients-physicians, p<0.017.5-Peripheral neuropathy pain -statistically significant differences between patients-physicians, p<0.017.6-Joint pain -statistically significant differences between patients-nurses, p<0.017.1-Pain in AIDS -statistically significant differences between patients-physicians, between patients-nurses and between physicians-nurses, p<0.017.2-Fibromyalgia -statistically significant differences between patients-physicians and between physicians-nurses, p<0.017.3-Joint pain -statistically significant differences between patients-physicians and between physicians-nurses, p<0.017.4-Low back pain -statistically significant differences between patients-physicians, p<0.017.5-Repetitive motion disorders -statistically significant differences between physicians-nurses, p<0.017.There were important divergences between studied samples in both methods and differences between patients and professionals are highlighted (patients-physicians, patients-nurses).These data suggest that professionals and patients have different perceptions regarding these types of pain.We observe that numerical values in both methods are underestimated by professionals.Compared to patients, professionals almost always presented smaller values.
We highlight that pain in AIDS presented the highest number of divergences between samples.There were differences between patients and physicians and patients and nurses in the magnitude estimation method and differences between patients and physicians, patients and nurses and also between physicians and nurses in the category estimation method.
Cancer pain was considered the most intense pain in the majority of the studied samples and in the different psychophysical methods used.Cancer pain is a frequent symptom in patients with cancer and presents significant intensity.This daily pain manifests itself in more than one place in the body and, when it is not continuous, it remains for several hours per day.Pain occurs in patients with cancer through several discomforts, such as "cutaneous lesions, unpleasant odors, anorexia, cachexia, lack of sleep, fatigue, anxiety, depression, experience of feeling mutilated and disfigured, anticipatory mourning, economic hardship, spiritual distress" (9) .
This author stresses that metaphors linked to cancer imply processes linked to a sentence of death, a "curse", a disease considered an "invincible destructor" (11) .
An interesting comparison between cancer and cardiovascular diseases corroborates the results of this study: "of all diseases, cancer is the one that causes the strongest psychological impact.Not only because of imminent death, which is the destiny of all of us, but because of its progressive and painful approximation, with potential natural or post-therapy mutilation.The risk of sudden death of cardiovascular diseases is less scaring.The perception that cancer is incurable, coupled with fear of its potential radical therapy and images of body alterations caused by its treatment, is terrifying" (12) .
Observing Tables 1 and 2, one can perceive that, for the outpatients' group, pain in AIDS occupies the third position, both in the magnitude estimation and category estimation methods.It is interesting to notice the outpatient group's concern with this type of pain.
Pain in AIDS does not figure among the ten most intensive types of pain in any of the methods used for the physician group and occupies the ninth place according to the nurses' group in the category estimation method.This type of pain presented statistically significant differences between patients and physicians and between patients and nurses in the magnitude estimation method.There were statistically significant differences in all samples (patients-physicians; patients-nurses and physiciansnurses) in the category estimation method.These findings reveal divergences between the perception of patients and professionals.
Greater concern with cancer pain than pain in AIDS is perceived.The individual with cancer, according to the stigma created for such diseases, "does not deserve" such suffering and, thus, is worthy of pity and attention.Individuals with AIDS, on the other hand, are not worthy of such feelings because of their "behaviors that could potentially lead to the disease".
A recent study (13) found that 67% of a sample representative of a population of adults with HIV reported pain during the four weeks previous to the interview.The authors stress that the pain related to HIV is caused by direct effects of the virus on the central and peripheral nervous system, immune suppression, treatments and several disorders associated to the virus presence.
Pain in AIDS has other important aspects to be taken into account, such as prejudice related to the syndrome, disfigurement, self-esteem disorders, rejection of family and friends, removal from work and leisure activities.Cancer pain and pain in AIDS present similar aspects.
However, the social aspect of pain perception should be kept in mind.Based on the analysis of results found in the study, we can infer that the meaning of this painful phenomenon is also influenced by the society itself, that is, it is affected by the stigma created for the disease that causes it.
Labor pain also occupies the third and fifth positions when considering physicians and nurses, respectively.For the outpatients' group, it occupies the eighth position.An anthropological study, carried out through the ethnographic method with participant observation and semi-structured interview, aimed to examine childbirth at a public maternity of a Brazilian capital, focusing on the perspective of young women and adolescents.Results revealed that women report that labor is dominated by fear, loneliness and pain.
"By the way, it confirms stories these women heard about labor pain out of the hospital, whether from relatives and friends, or the media in general".They stress the absence of a companion during labor for institutional reasons, which would produce a greater sense of security and better coping.The authors consider that cultural meanings are inseparable from physical sensations (14) .
The study mentioned above can help in the discussion of the results appointed here.Although labor pain is related to childbirth and not to a disease or life-threatening process, it was considered one of the most intense pain types.We have to bear in mind that the approach of the childbirth process in Brazil is precarious and generates feelings of fear, loneliness and abandonment, which lead to higher tension levels and increased painful perception.Another observation is that pain considered of lower intensity, like those caused by repetitive motion disorders, joint pain and low back pain, are types of pain with high prevalence in the population, with high frequency in daily life, and cause physical and social incapacity (15)(16)(17) .However, It indicates that the rank of pain intensity obtained from the estimation of the two methods presents concordance for the three groups and also that the estimates are statistically significant, p<0.001.
There are some essential differences in the obtained scales.It is possible to establish the rank, the differences and especially the ratios between the degrees of pain intensity in the magnitude estimation method.In the category estimation method, on the other hand, it is only possible to establish the rank and differences between pain intensities.In the rank estimation method, only the rank of pain intensities can be obtained.
Authors of a previous study (18) stress that there are two main problems with the use of category scales.First, because the number of categories with which stimuli are judged is fixed the method introduces some biases.This is the reason why category scales are especially sensitive to contextual effects, such as amplitude of categories and frequency of stimuli.In the case of pain measurement, a large source of error is the embarrassment caused to the participant by the imposition of an upper limit at the end of the continuum of pain, that is, at the end of the pain measurement scale.Second, category scales do not permit statements regarding difference ratios between the obtained measures.It is possible to say that a measure is larger than the other or subtract one from the other, but it is not possible to infer to what extent one measure is larger or smaller than the other.
In the category estimation method, it is not possible to know the ratios between pain intensities, that is, one cannot tell to what extent cancer pain is considered more or less intense than burn-injury pain.
We can say, by observing score (seven) to the type of pain with the highest intensity and assign the minimum score (one) to the type of pain with the lowest intensity.The other intermediary scores, two to six, should be used to indicate intermediary degrees of intensity according to participants' perceptions.The different types of pain were randomly presented to each individual.Each individual established one score for each type of pain.

CONCLUSIONS-
Cancer pain, myocardial infarction pain, renal colic, burn-injury pain and labor pain were considered the most intense types of pain, regardless of the method used or sample studied, in addition to pain in AIDS, considered by the outpatients' group one of the most intense pain types.-Pain in temporomandibular joint disorder, joint pain, repetitive motion disorder pain, menstrual colic and low back pain were considered the least intense types, regardless of the method used or sample studied.-Ranking of intensities for different types of pain, comparing the different psychophysical methods used, resulted in a significant level of concordance.-This study permitted deeper reflections on the perception of the painful phenomenon and its meaning in our culture, comparing professionals and patients through a valid and reliable method.There were divergences in the perception of intensities of some types of pain, mainly between professionals and patients (physicians-patients, nurses-patients).-A profile of perception of different types of pain in our society was established.The data collected raised original characteristics for this study.Such characteristics are shown through the comparison of different types of pain judged by different samples.

Table 2 -
Geometric average of category estimates (CE) for the different types of pain by ranking (R) according to outpatients, physicians and nurses.HCFMRP/USP, 2007 are not life threatening and are related to work, gender, age, stress, sedentariness, among others.

Table 2
, that menstrual colic (ME=317.31) is considered by the physicians' group about twice more intense than preoperative pain (ME=159.83);while the nurses' group considered cancer pain (ME=310.50)twicemore intense that pain in peripheral neuropathy (ME=154.24).These comparisons can also be carried out between the groups.For example, we can state that pain in AIDS is considered two and a half times more intense by the outpatients' group (ME=303.60)