Worldwide, 176 million women experience endometriosis.1 Endometriosis is a gynecologic chronic condition, characterized by the presence of endometrial-like tissue outside the uterus that induces an inflammatory reaction and frequently leads to painful symptoms and/or infertility.2,3 Despite increasing research interest, the pathogenesis of endometriosis is still poorly understood, and existing theories seem to show a range of limitations.4 As regards the pathogenesis of endometriosis, recent hypotheses suggest the involvement of: (a) genes and Wnt/β-catenin in the aberrant placement of stem cells4; (b) immune cells, adhesion molecules, extracellular matrix metalloproteinase and pro-inflammatory cytokines in the development of positive conditions for ectopic endometrial cells4; (c) endometrium and peritoneum5; (d) reactive oxygen species (ROS) and oxidative stress.6 Furthermore, giving an established diagnosis of endometriosis is a controversial issue. In this regard, there is an increasing medical interest to the importance of differential diagnosis between endometriosis and other medical conditions (eg, interstitial cystitis/painful bladder syndrome) with similar symptomatology, which are frequent comorbidities, and may lead to misdiagnosis and mistreatment.7,8
Women with endometriosis usually report pelvic or abdominal pain, dysmenorrhea, dyspareunia, dyschesia, and/or dysuria, vomiting, nausea, and heavy and/or irregular bleeding. Pain is usually described as “sharp,” “stabbing,” “horrendous,” “tearing,” “debilitating,” and “breath-catching.”9 The impact of pain is dynamic, and its experience differs between women, and it is independent of the stage of the disorder.10 Indeed, it may be reported every day, once a month, or rarely, and it changes individually over time and across life stages.11
Because of its features, pain is known to severely affect the quality of life and mental health of women with endometriosis.2,9,12–19 The influence of pain is so challenging that different authors have suggested that it is the painful symptomatology (and not the endometriosis itself) that negatively impacts women’s lives and causes distress.12,16,17,20
However, mechanisms that underlie pain in this population are still poorly understood. A recent study by Coxon et al21 has suggested that changes in both peripheral and central nervous systems might be involved. In particular, endometriosis-associated pain may include reduced innervation of the sympathetic nervous system, increased sensory innervation and changes in the inflammatory markers in the peritoneal fluid, and changes in the activity and connectivity of different brain areas, altered brain area volumes, dysfunctions of the hypothalamic-pituitary-adrenal axis (HPA), and altered psychology.21
Literature suggesting that psychological or cognitive factors may be involved in the pain experience is widening. According to the biopsychosocial model of chronic pain and disability, the experience of pain is the result of a dynamic interaction between physiological, psychological, and social factors. Complex factors such as emotions, cognition, and previous experiences may contribute to the variation and modulation of the pain experience.22 In particular, the relationship between psychological/cognitive factors and pain experience seems to be related to the following: (1) the fact that some individuals are more prone to respond to pain in an anxious and avoidant style23; (2) the mediation of neurophysiological mechanisms including the role of periaqueductal gray, amygdala, anterior cingulate cortex, and anterior insula24; and (3) increasing attentional focus on pain (ie, processing preferentially pain-related information and misinterpreting even ambiguous feelings as painful).25,26
Studies of women with endometriosis, studies have suggested that pain experience, pain-related distress, and treatment outcomes may be modulated by psychological and cognitive aspects,27 and high levels of emotional distress may intensify the severity of pain perceived.10 In particular, recently, a hypothesis has been advanced that personality and coping strategies may influence pain experience in this population. However, the role of these factors has not been investigated much, and it is still poorly understood. A few studies of personality traits have found a role of worry traits, assertiveness, harm avoidance, and novelty seeking in influencing pain experience in this population.15,28,29
In addition, coping strategies seem to play a significant role in endometriosis. Coping strategies refer to the specific behavioral, emotional, or cognitive efforts that individuals use to master, tolerate, reduce, or minimize stressful events.30 In order to cope with pain, patients with endometriosis are known to engage in the following coping strategies: scheduling everyday activities around menstrual cycle, engaging in self-management (eg, alleviating pain and discomfort through taking analgesics, relaxation, or controlling diet), seeking for social support, trying to think about the disorder in a different way, evoking spirituality, or adopting a positive attitude toward the condition.31–33
Coping strategies in this context are central, as the way an individual copes with a stressor may mitigate or exacerbate the levels of stress experienced, leading to a series of positive or negative mental and physical outcomes. The literature has suggested a significant role of some coping strategies in influencing the experience of pain. A recent critical narrative review of Zarbo et al33 on women with endometriosis reached the following conclusions: (1) women with pelvic chronic pain related to endometriosis are more likely to repress emotions than healthy women; (2) suppression of emotions, pain catastrophizing, and passive coping style are associated with higher self-reported pain; and (3) some positive coping styles (eg, detached, rational, focused on the problem) are related to better mental health and adaptation to stress. In addition, a crucial role of beliefs and thoughts in this population has been suggested for a wide range of domains (eg, quality of life related to infertility, sexual distress).34,35
However, even though the interest on the mental and cognitive component of pain experience of this chronic condition has widen in the last few years, no study has deeply focused with a mixed-method study on the association between psychological/cognitive factors and pain experience in women with endometriosis. In recent years, interest in mixed-methods research is expanding in different disciplines.36 When used in combination, quantitative and qualitative methods complement each other and allow for more robust analysis, taking advantage from the strengths of each.37 In this field, qualitative and quantitative data integration may help generate new insights, such as the identification of the pattern of relationships between different variables.
Therefore, the purpose of this study was to investigate the association between pain experience and psychological/cognitive factors (ie, worry personality traits and coping strategies) in a sample of women with endometriosis.
MATERIAL AND METHODS
The present mixed-method sequential explanatory study consists of 2 different phases: quantitative followed by qualitative. According to Creswell et al,38 we first collected and analyzed the quantitative data. Thereafter, the second qualitative phase was built on the basis of the first quantitative one, with the aim to refine and explain statistical results by exploring participants’ views more deeply.39,40 After these 2 phases, both quantitative and qualitative analyses have been connected in a third one, which combines both, leading to the metainference of the study.41
The entire study was conducted in accordance with APA42 ethical standards for the treatment of human experimental volunteers; each participant provided consent in compliance with the Declaration of Helsinki.43 The study was approved by the ethical committee of the local institution.
Participants and Procedure
From December 2016 to April 2018, women with a diagnosis of endometriosis were recruited. We included women with a diagnosis of endometriosis, without past or concurrent neurological and psychiatric disorders or severe medical conditions, and who were able to write and read in the Italian language. Women who accepted to participate completed a battery of self-reported validated questionnaires, through paper-and-pencil or web-based administrations.
A total of 162 women were enrolled in this first quantitative phase and completed the battery. Sixty of them were recruited from a Hospital in North Italy, while 102 were recruited from virtual mutual support groups, medical forums, and web associations.
From October to November 2018, participants who were allocated to the high-pain group in the first quantitative phase were contacted to request participation to the qualitative step of the study. In this phase, we used a multiple case study approach44 to help explain the pain, its manifestations, its consequences, and its association with coping strategies and worry traits. A case study can be defined as an intensive study about a person, a group of people, or a unit, that has the aim to generalize over several units.45 A multiple case study design includes >1 case, and the analyses are performed at 2 levels: within each case and across the cases.44
A total of 6 women accepted to take part in this phase. They were subjected to a semistructured interview performed face-to-face in Hospital or by telephone. Interviews were audiotaped and transcribed. The interviews lasted about 45 minutes and were carried out by trained clinical psychologists.
Sociodemographic and clinical information were collected by means of a structured ad hoc questionnaire. We collected information about age, civil status, nationality, occupational status, education, family status, body mass index, and lifestyle (ie, smoking habits). Moreover, we assessed the presence of past and present chronic medical conditions in comorbidity with endometriosis, and clinical information about endometriosis (eg, previous and current treatments, localization, stage, symptomatology history).
Pain intensity over the last 3 months, worry traits, and coping strategies were assessed by means of the Italian version of validated questionnaires.
The Short-Form McGill Pain Questionnaire (SF-MPQ46) is a self-report scale for the evaluation of pain severity that includes 15 items and 2 subscales: affective and somatic. A total score, ranging from 0 to 45, can be obtained summing all items. Pain intensity for each adjective related to pain experience is assessed on a scale from 0 (none) to 3 (severe). In this study, we decided to ask the participants to answer the questions referring to their experience of the last 3 months.
The Penn State Worry Questionnaire (PSWQ47,48) is a self-report questionnaire including 16 items that allows the assessment of worry traits (ie, the habit of worrying in general, regardless of the circumstances). The total score of the scale ranges from 16 to 80. Higher scores suggest the higher presence of worry trait. The cutoff of 45 identifies the worry trait with 99% sensitivity and 98% specificity.49 Both the original version and the Italian validation showed good internal consistency.47,48
The Cognitive Emotion Regulation Questionnaire—Short Version (CERQ-short50) is a self-report multidimensional scale that includes 18 items aimed at assessing coping strategies in terms of individuals’ thoughts after having experienced a negative event. Cognitive coping strategies refer to rather stable styles of dealing with negative life events. The scale includes 9 subscales, which are self-blame, acceptance, rumination, positive refocusing, refocus on planning, positive reappraisal, putting into perspective, catastrophizing, and other blame. Each subscale may obtain a score ranging from 2 to 10. A higher score in each scale suggests the higher presence of that cognitive coping strategy. The scale has demonstrated good reliability and validity.50
On the basis of findings obtained from quantitative analyses, an ad hoc semistructured interview was developed. The interview consisted of 6 open-ended questions concerning clinical history, pain experience, its manifestations, emotions and beliefs related to pain, and coping strategies used to face it with. The interview began with the clinical psychologist introducing herself and the general aim of the study and was followed by “small talk” to create a relaxed atmosphere. No detailed information about the core aim of the study was provided to participants in order to not influence their narrations. Before starting the interview, the interviewer collected the pain experience severity over the last 3 months, by means of a Numeric Rating Scale from 0 to 10.
Questions were developed on the basis of previous literature, and findings emerged from the first phase. Examples of questions are “try to focus on the pain related to the pathology. How does it manifest? Which characteristics does the pain have? Which adjectives would you use to describe it?” or “Usually, how do you react to pain? Are there recurring behaviors or thoughts/emotions?”. During the interview, the clinical psychologist let each woman describe her experience as spontaneously as possible. Moreover, probe questions such as “Can you give an example?” or “Can you clarify this concept?” were used to reach a deep understanding of the matter and to clarify parts of the interviews.
Preliminary analyses were performed to ensure no violation of the assumptions of normality, linearity, multicollinearity, singularity, homoscedasticity, and independence of residuals. Standardized scores and box plots were used to identify univariate outliers. Variables with values ±3.29 SD from the mean were considered outliers.51 Outlier values were brought into the range.51 Normality was assessed for each variable by examining box-plots, stem and leaf plots, histograms, and skewness and kurtosis values.
First, we calculated Pearsons’ P correlation in order to investigate relationships between variables. Thereafter, independent sample t tests have been performed for assessing coping and personality differences on the basis of pain severity. Low and high-pain groups were created on the basis of median score on SF-MPQ total score. The 2 groups (low pain [LP]; high pain [HP]) were inserted as independent variables, and CERQ-short subscales and PSWQ total score as dependent variables. Effect sizes were evaluated using Hedges g and interpreted according to the guidelines (ie, small effect >0.2; medium effect >0.5; large effect >0.8).52
All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) version 23.0. All statistical tests were 2-sided; a P-value ≤0.05 was considered significant.
Verbatim transcripts of the semistructured interviews were analyzed using Interpretative Phenomenological Analysis (IPA), an approach that allows investigating “how individuals make sense of their lived experiences.”53,54 In particular, it permits to analyze, interpret, and represent the personal world of participants exploring beliefs, attitudes, and feelings.54 According to IPA methodology, each transcript was read numerous times, and then the researchers inserted keywords and notes of thoughts, observations, and reflections on the left side of the transcripts. Thereafter, the keywords were grouped into themes. After this, researchers looked at patterns across cases and grouped themes into “clusters” or higher-order themes.
According to the convergence model, which represents the traditional model of mixed-method triangulation design,55 data obtained from the first and the second phases were collected and analyzed separately and then combined at the point of interpretation into a meta-matrix, comparing and contrasting the findings emerging from the same phenomenon.36,56,57 Meta-matrix, a second-level analysis used for triangulation, facilitated data examination and allowed recognition of pattern across data sets.58
Preliminary analyses revealed no issues with normality, linearity, multicollinearity, singularity, homoscedasticity, and independence of residuals.
Correlation analyses revealed high statistically significant correlations between almost all measures (Table 1). Almost all subscales of the CERQ-short highly correlated with each other. Furthermore, positive statistically significant correlations were found between SF-MPQ total and PSWQ (r=0.320), self-blame (r=0.154), and catastrophizing (r=0.268). Therefore, a high correlation emerged between pain severity over the last 3 months and worry traits, self-blame (ie, thoughts of blaming for what one has experienced), and catastrophizing (ie, negative emphasize of experiences).
Independent sample t test revealed significant effect of group (ie, HP; LP) for PSWQ (t=−3.764, P<0.001, Hedges g=0.591), rumination (t=−2.125, P=0.035, Hedges g=0.332), and catastrophizing (t=−2.582, P=0.011, Hedges g=0.406). Results evidenced that the HP group had significantly higher scores on worry traits, rumination, and catastrophizing than the LP group (Table 2).
The high-order themes that emerge from IPA analyses are pooled by the concept of “control,” which emerged in several narrations and from different perspectives. High-order themes that emerged by the narrations, described in detail below, were as follows: (1) pain controls women’s lives; (2) medical control of the pathology and symptomatology; (3) individual attempts to control pain; and (4) thoughts’ control (Fig. 1).
Pain Controls Women’s Lives
Pain, differentiated as chronic and acute, has been reported as one of the main concerns of women with endometriosis. Chronic pain refers to a general unlocated ache maintained almost all days. Conversely, acute pain manifests as an unpredictable intense localized short cramp.
Acute pain is described with adjectives such as stinging, hot or which burns, pounding, shooting, sharping, tiring, devastating, terrible, and disabling. It has been compared with an “unpredictable shake,” “like a tight knot,” “like a tight ball,” “as if something is going to explode,” and “like a dagger which plugs.”
In addition, both acute and chronic pain are usually related to fatigue, swelling, dizziness, fainting, pressure problems, colic, leg pain, difficulty in walking, and headache. The pathology in some cases leads to other medical complications, such as issues during pregnancy, difficulties getting pregnant, miscarriages, loss of teeth, bleeding from the rectum, body and weight change, and bladder and evacuation problems.
It’s just like if that part of my body is going to swelling (…) as if there is something that is going to explode
It was annoying, pungent and I do not know how, it hammered
The pathology is so significant that several women reported a range of psychosocial negative consequences, such as reduction of time invested in education/work/hobbies, economic and social dependence on others, loss of interest and desire, embarrassing situations that led to frustration or anxiety, body changes and subsequent negative image of oneself, and difficulty in everyday planning. Furthermore, participants declared to usually report negative feelings like fear, agitation, anxiety, tension, anguish, powerlessness, guilt, hate, jealousy, despair, and anger, and also disgust and shame toward oneself and one’s body. In particular, anger has been reported as a positive emotion, which makes one alive and stimulates to react, as the opposite of powerlessness. In addition, the pain has been described to be part of oneself, of the person’s own identity.
It (the pain) influenced many aspects (…) also influenced me in the desire to do (…), it blocked me, and this bothered me because I always liked being outdoors, going out … but this was something that I could not control, and this is the matter that bothered me the most
I just hated myself, I wanted to tear my stomach, I was disgusting myself, I said I want another’s stomach. Why does that woman is fine, and I always feel bad?
It’s a pain that is part of me
Medical Control of Pathology and Symptomatology
From descriptions of participants emerged a range of complaints and worries as regards the medical difficulties in both diagnosis and treatments of the pathology. The diagnosis of endometriosis arrived after a long time from the onset of symptomatology, it was often misdiagnosed and confused with other pathologies, and the symptomatology underestimated. Indeed, participants frequently reported that they were not believed for a long time and that everyone, including doctors, underestimated the symptoms and were inclined to normalize them.
Furthermore, they complained about the difficulties related to the medical control of the pathology, both surgically and medically. Indeed, treatments were frequently unsuccessful and related to a series of complications and consequences. Some of them, despite having undergone >5 surgeries for endometriosis, still have serious symptomatology. Sometimes, surgery is not recommended due to possible medical damage that may arise.
At the beginning, they told me that it was a problem in my head, that it was stress … And then they started telling me that it could be a problem of nutrition, but, in the end, instead, it was endometriosis
I thought I was tragic, my mom told me it was normal that you feel bad when coming menstruation, but I did not think so bad
In addition, most of them indicated the need to have more information about the pathology and symptomatology in order to recognize pain, reduce anxiety, and be more aware of what is going to happen to their body. Indeed, awareness of symptomatology would help them to better control it. In this context, patient-doctor communication seems to be crucial for increasing awareness and, in turn, reducing feelings of powerlessness and anxiety.
I wanted to have some more tools, even on a scientific level, to better understand my pathology and what I had and what it was developing. I think it could give me a motivation to react (…) I would need something more, something of objective on which to base on … it would feel me better, it would give me a reason of what happened to me and perhaps I would have reacted differently
Individual Attempts to Control Pain
Acute pain is described by participants as both unpredictable and difficult to control. They are not able to prevent its onset or actually know when it would occur or how intense it would be. Sometimes, acute pain occurs when women are in a state of psychological distress: for example, when they are stressed by the environment (eg, arguments with intimate partners or familiars, or stressful demands at work) or, conversely, when they are trying to relax (ie, when the mind is “free” and negative thoughts arise, and they are more attentive toward the symptomatology).
Every day I do not know how I’ll be in the next six hours, I cannot afford to take a trip by car for an hour, I cannot go shopping alone (..) it is like a trick of the mind: you still have legs, you can get out of bed and go to the bathroom (…) but you always really have that anguish that from there two hours you’re dead and you have to count on others (…) the sense of unexpected, you can never predict anything
It happened once, then it can happen again… the worsening is around the corner, and living with this anxiety is really difficult
Very often there is no logical link other than stress. Maybe, the family problems, stress at work or whatever we stressed out put us at risk to inflammatory level, so maybe something that is latent then breaks out (..) it strikes you there … Because your weakness is there …
When I relax, on Saturday or Sunday, or any days that I know that I have no deadlines, pressures, things to do urgently, and I relax … then I’m sick, I was sick, I was worst …
Focusing my thoughts only there, in the physical point where I had that tremendous pain did feel me more that point
Furthermore, acute pain is difficult to control and coping strategies used to face it are frequently ineffective. Among coping strategies, the most frequent are as follows: search for information about pain, seek for support on virtual support groups, take medications, try to relax, change positions, put something warm on the stomach, have a warm shower or bath, try to control intrusive and catastrophizing thoughts or focus on something else, avoid situations (eg, hobbies) that may increase pain, search for complementary treatments (eg, autogenic training, acupuncture), and try to accept the condition.
The inability to prevent and control the onset of pain, and the implementation of ineffective coping strategies, leads women to develop strong feelings of powerlessness.
A kind of impotence, even if you want, it is like you have a black veil in front of your head, something that … a cape … something that presses on the head and you want to do something, but you cannot do it
In reaction to pain, participants declared experiencing feelings of agitation, anxiety, nervousness, and powerlessness, and to have a range of automatic invasive thoughts, frequently also catastrophizing. In particular, ruminating and catastrophizing thoughts occur both during pain experience and before its onset. Indeed, participants reported anticipatory concerns about acute pain and its possible future severity also when it has not yet occurred or when mild pain is arising. Indeed, pain is often “a worm in the head.”
When I knew I had to stop the pill, I felt sick just thinking about it
At the first pain, I thought again and imagined the bad things
Negative thoughts that usually arise in concurrence with pain assume ruminative and often even catastrophic characteristics. These thoughts concern the possibility of new endometrial formations or the onset of other pathologies, anxiety about the need to get pregnant as soon as possible, the duty to keep control, fear of what may happen in the future, self-blaming, and fear of death that could be due to pain.
The only thought is “who knows what it is?”. If it is only the adhesion that was already there in the last visit, if new ones have been created, if it is something else (…). I think on all what is connected, I think I should go for a visit, because maybe it’s a few months since I’ve done it. (…) when the pain comes, automatically the thought goes there and to the connected things
When I have a little cramping in other new points, then the thought automatically goes to what could be different from this
When the pain comes you cannot think about anything else (…) you think to death, the pain so strong that you die … but slowly …
When negative thoughts arise, participants usually try to control them. However, the effort to control intrusive and catastrophizing thoughts reveals an inefficient coping strategy. Indeed, most of the participants reported that trying to control thoughts usually leads them to distress, anxiety, and feelings of powerless, because they frequently fail in their attempts.
I try to not think about it but it’s there, it’s like a stone attached to me, that stabs me
As shown in Table 3, from the meta-matrix emerged a strict association between pain and worry traits/coping strategies. The main stressors and concerns in the life of women with endometriosis are acute pain experience, persistent fear of its occurrence, its unpredictability, and the difficulty in controlling it. Participants showed a series of worry trait characteristics (ie, the need for control, anticipatory fear, intrusive worries about future) and maladaptive thoughts such as coping strategies (ie, self-blame, rumination, catastrophizing) as means to cope with stressors (ie, acute pain, in particular). In order to control acute pain, participants usually engage in unsuccessful strategies, and the difficulty in controlling it reinforces negative thoughts and improves the feelings of powerlessness, leading in turn to psychological distress/anxiety.
From this exploratory mixed-method study emerged a strict link between pain and worry trait/coping strategies. From quantitative analysis emerged a significant correlation between pain intensity and worry traits, self-blame, and catastrophizing; in addition, it emerged that women with HP have higher levels of worry traits, and rumination/catastrophization as coping strategies. From qualitative analysis emerged that pain affects different domains of the participants’ life, is related to a range of physical and psychosocial negative implications, and causes a series of negative emotions/feelings (ie, fear, anxiety, tension, powerlessness, guilt, and anger) and ruminative/catastrophizing thoughts (concerning past and future—like new endometrial formations or other pathologies—and self-blaming). Furthermore, the unpredictability of the pain, the need for “control” (of pain, symptomatology, and thoughts), and the subsequent powerlessness due to the failed attempts seem to be crucial in determining psychological distress related to pain in this population.
Findings from this mixed-method study are particularly innovative, as they allow to better explain the association found by previous studies between pain severity and personality traits/coping strategies in this specific population.28,29,59–61
Interestingly, from the triangulation of quantitative and qualitative results, a model of onset and maintenance of pain in women with endometriosis emerged (Fig. 2). As described in the figure, psychological distress (in terms of stress from the environment or ruminative thoughts) may lead to the experience of acute pain (possibly due to neurophysiological or attentional reasons).23–26,62 The onset of acute pain is related to an automatic need to control it that brings the woman to engage in a range of unsuccessful coping strategies. The failure of these attempts leads to a series of negative feelings and emotions, among which the most predominant is the powerlessness. Failure of coping strategies and powerlessness reinforced the ruminative, self-blaming, and catastrophizing thoughts, which automatically arose after the onset of pain. Because of the fact that these thoughts are unpleasant, the unconscious reaction of the women is that of trying to control them (ie, trying to suppress them). However, the more they try to control thoughts, the more the thoughts are maintained, and, the number of intrusions experienced extend.63 As a result of these multiple failed control attempts, the feeling of powerlessness and, in turn, the psychological distress will be reinforced.64 Thereafter, a vicious circle is triggered, and the woman will experience increased pain.
Despite the advantages of the methodology utilized and the pioneering findings that emerged from this mixed-method study, a series of limitations should be considered: the limited sample size for the qualitative interview, a part of the administration of the battery of questionnaires was web-based, and some of the interviews were carried out by telephone.
In conclusion, from the study emerged a range of clinical implications for the medical team and psychologists. Indeed, the nucleus of worry personality—characterized by the need for control, anxiety, mental preview of acute pain, negative intrusive and catastrophizing thoughts, negative metacognitive beliefs about the uncontrollability of thoughts—seems to be relevant and should be considered as a risk factor when taking into account women with endometriosis. In particular, worthy of attention in this context are the negative metacognitive beliefs related to the uncontrollability of thoughts and their relationship with psychological distress. Indeed, according to the metacognitive model of Wells,64 different attempts to control the nature of thinking (ie, trying to suppress certain thoughts, analyzing experiences to find responses, or predicting the future) are counterproductive in the long term and may lead to the onset of psychological disorders. Furthermore, psychological disorders might, in turn, cause greater pain experience10,27 and reinforce a harmful vicious circle. Treating beliefs about the uncontrollability of thoughts would reduce feelings of powerlessness and psychological distress and, in turn, decrease acute pain experience.
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