FormalPara Key Summary Points

Why carry out this study?

Patients with painful diabetic neuropathy endure severe and excruciating pain that adversely affects their function. According to Melzack theory, one of the most important factors in pain perception is psychological factors.

Before this study, no clinical trial study had been performed to measure the effectiveness of psychological therapy in reducing the severity of pain perception in patients with painful diabetic neuropathy.

The main purpose of this study was to investigate the effectiveness of acceptance and commitment therapy (ACT) therapy on improving pain acceptance and subsequently reduction of pain perception.

What was learned from the study?

The results showed that compared to the control group, the interventional group had significant improvement in pain acceptance and also a major reduction in pain perception in the post-test phase. The same results were observed after a 3-month follow-up.

Introduction

Pain is a multidimensional phenomenon that can affect different aspects of one’s daily functions. Interdisciplinary approaches to pain concentrated on the biopsychosocial model. This model emphasizes psychological factors in pain perception, such as thoughts, emotions, and behaviors [1,2,3]. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), pain disorders form an independent classification of psychiatric disorders. Chronic pain is considered in other illnesses such as diabetes, fibromyalgia, rheumatism, migraine, and somatic symptom disorder [3, 4].

Painful diabetic neuropathy (PDN) diagnosis is based on the patient’s description of pain, such as burning, deep aching, or sharp sensation. PDN is caused by dysfunction in nerve fibers. Neuropathic pain is usually severe and chronic and can negatively affect the biological and psychological functions of patients with diabetes. The estimated rate of PDN prevalence is 25–30% [5,6,7,8].

Different bio-physiological (acupuncture, laser therapy, and pharmacotherapy) and psychological (mindfulness and cognitive behavioral therapy) approach for pain management used [9,10,11]. The treatment at the forefront for neuropathic pain is pharmacotherapy, especially pain sedatives, opioids, cannabis, and antidepressants. All of them have significant side effects [12,13,14]. According to Melzack’s theory, psychological factors might affect pain severity perception, and pain could exist despite typical clinical examination results [15, 16]. Kioskli et al. in a systematic review, indicated that depression, anxiety, poor sleep, and low quality of life are consequences of PDN [17]. Various studies on chronic pain show that acceptance might improve pain management [18,19,20]. McCracken has described pain acceptance as experiencing chronic pain without trying to eliminate or avoid it [19,20,21].

Cognitive behavioral therapy (CBT) is one of the psychological therapies for chronic pain. The aim of the CBT approach is the identification and alteration of thought content [18, 22,23,24]. In recent years, the third-wave of cognitive behavioral therapies used for psychological disorders. These interventions of CBT have beneficial for pain management in chronic pain patients. One of the third-wave of cognitive behavioral therapies is acceptance and commitment therapy (ACT), which emphasizes acceptance and willingness to experience unpleasant events. The aim of ACT is facing, acceptance, and change the patient's relationship with pain experience and psychological flexibility.

Research results about chronic pain, show that ACT increases pain acceptance and decreases pain perception, and pain severity [20, 25, 26]. According to Xianghua Xu's (2019) study on pain acceptance in cancer patients with chronic pain, acceptance-based CBT could increase tolerance and reduce pain perception [27].

Furthermore, studies show that there is a negative correlation between pain acceptance and pain perception [28]. McCracken argues that pain acceptance consists of two elements: pain willingness and activity engagement. Pain willingness refer to strategies for adaption and coping with pain. Activity engagement emphasizes continuing daily activities and taking actions towards values despite focusing on the unpleasant experiences of pain [24, 28, 29]. The previous biological treatments for neuropathic pain had limitations such as being unable to the assessment of psychological factors affecting pain, and the proper literature review of ACT, in chronic pain. This study aims to assess the effectiveness of ACT (focusing on the acceptance component) in a sample of patients with PDN.

Methods

Trial Design

The present study is a randomized controlled trial that includes the pre-test, post-test, and 3-month follow-up stages. The intervention was parallel in both groups and performed simultaneously.

Participants

This was a single-blind randomized clinical trial conducted in the control group and intervention group. Moreover, pre-test and post-test design with a follow-up of three months used. The study population consisted of all patients diagnosed with diabetic neuropathy by a neurologist referred to the Psychiatric Clinic of Farabi Hospital, Kermanshah, Iran, between 15 April 2019 and 31 May 2019. The first step was the examination of patients with diabetes and neuropathic pain performed by a neurologist, and they were referred to a clinical psychologist in the psychiatry clinic at a university-affiliated hospital. The study inclusion criteria were those diagnosed with diabetic neuropathy by a neurologist on the basis of a clinical status examination, a patient's informed consent to participate in the study, age range of 35–65 years, having at least third-level middle school education, no psychiatric treatment during the previous year, no history of alcohol and drug abuse, and no history of somatoform disorders [30, 31]. Participants excluded from the study on the basis of the following criteria: drug abuse during the intervention and follow-up, those who were absent for more than two sessions, and the patient's unwillingness to continue the treatment. Participants signed a consent form. Finally, they entered the treatment program and were assessed in the pre-test phase.

Therapeutic Interventions

This study was conducted by a therapy program based on the theoretical model of acceptance and commitment therapy for chronic pain [20]. It consists of eight sessions a week (Table 1).

Table 1 A summary of the contents of ACT sessions
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Measures

Demographic Characteristics Questionnaire

This questionnaire consists of demographic variables such as age, sex, marital status, educational level, and job status.

McGill Pain Questionnaire (MPQ)

Melzack developed the MPQ in 1975. It consists of 20 subcategories of verbal (single-word) pain descriptors. The Short-Form McGill Pain Questionnaire (SF-MPQ) was also developed by Melzack et al. to provide a brief, but useful measure of pain used in 250 studies. The McGill Pain Questionnaire consists of two independent factors: the first factor is sensory pain describing an individual's experience of pain, and the second one is the emotional pain describing the psychological consequences of it. The reported Cronbach’s alpha coefficient is 0.85% [32,33,34].

Chronic Pain Acceptance Questionnaire (CPAQ)

The CPAQ is an assessment tool for chronic pain that each subject should answer for every item using a 7-point Likert scale. Each item scored on a 7-point Likert scale, ranging from 0 (never) to 6 (always), and the items for pain satisfaction scale scored reversely, ranging from 0 to 120. Higher scores indicate higher levels of pain acceptance. The Persian version of the CPAQ also showed adequate psychometric properties. The assessment of the psychometric properties of the Persian version showed that the CPAQ had a Cronbach’s alpha of 0.89 and test–retest reliability of 0.71 [35, 36].

Randomization

The sample size calculation was obtained from the following formula [37]:

$$ \frac{{\left( {Z_{1 - \alpha /2} + Z_{1 - \beta } } \right)^{2} \left( {s_{1}^{2} - s_{2}^{2} } \right)}}{{\left( {\overline{X}_{1} - \overline{X}_{2} } \right)^{2} }} $$

where α = 0.05, β = 0.08, s1 is the standard deviation of the first community, s2 is the standard deviation of the first community, \(\overline{X}_{1}\) is the average of the first community, and \(\overline{X}_{2}\) is the average of the second community.

This study was conducted according to the clinical trial method. The sample size was 50 participants. In this study, participants were divided into the interventional group (n = 25) and control group (n = 25). In accordance with the diagnosis of the neurologist, all participants received conventional medications to manage neuropathic pain. The intervention group received acceptance and commitment therapy for eight sessions. The results in the three phases of pre-test, post-test, and follow-up were evaluated. At the beginning of treatment, after completion of treatment, and a follow-up period of 3 months, the pain acceptance and pain perception questionnaires were administered.

Prior to the study, a therapy process familiarization session was conducted to justify the patients.

Statistical Methods

Statistical analysis and generation of descriptive statistics (e.g., frequency, mean, standard deviation) and inferential statistics (e.g., repeated-measures test ANOVA) were performed by SPSS software version 22.

Ethical Considerations

Ethical issues and the study were explained to the study participants. All participants signed a consent form before the initiation of the research and were assured that their identities and information would be kept confidential. The tools were filled in anonymously, and an ID code used to maintain the confidentiality of personal information. The research ethics committee of Kermanshah University of Medical Sciences approved the study (IR.KUMS.REC.1397.939). This study was registered at the Iranian Registry of Clinical Trials (IRCT20180205038630N4). The study was conducted in accordance with the Helsinki Declaration of 1964 and its later amendments.

Results

Three patients in the intervention group were excluded because of unwillingness to participate in the study. Two other persons were excluded because of disease severity. In the control group, two patients were excluded because of illness severity, and two persons did not participate in the follow-up period; therefore, a total of 41 subjects participated. Figure 1 shows the flowchart of the study.

Fig. 1
figure 1

Comparison of mean score of pain perception between ACT group and control group in the pre-test, post-test, and follow-up phases

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Regarding demographic variables, there were no significant differences between the two groups for age, diabetes history, educational level, and marital status (p < 0.05) (Table 2).

Table 2 Comparison of variables between ACT and control groups
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In this study, to evaluate the research hypotheses, data distributions were assessed for normality; the results of the Shapiro–Wilk test showed that the data were distributed normally (p > 0.05).

Pain Perception

To compare this variable between the study groups, a repeated-measures ANOVA used. For this purpose, the assumption evaluated the equality of covariance matrices, and then the results of Box’s M test met the equality of covariance matrices (Box's M = 16.03, p = 0.96). The assumption of homogeneity of variance was met between different levels of measurement (p > 0.05).

The assumption of homogeneity of variance was met between different levels of measurement (p < 0.05). Mauchly’s test of sphericity showed that the assumption of sphericity (p = 0.51 and Mauchly's W = 0.51). The results of the within-group tests showed that the effect of time was significant (F = 4.13, p = 0.02, partial eta squared = 0.09) as was the interaction effect between the time and the groups (F = 5.70, p = 0.005, partial eta squared = 0.13) (Table 3 and Fig. 2).

Table 3 Repeated measures ANOVA for comparison of pain perception and pain acceptance between ACT group and control group in the pre-test, post-test, and follow-up phases
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Fig. 2
figure 2

Comparison of mean score of pain acceptance between ACT group and control group in the pre-test, post-test, and follow-up phases

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Because the effects of time and the interaction between time and the groups were significant, a repeated-measures ANOVA was separately used for each study group. Mauchly’s sphericity test showed that the assumption of sphericity was met for both the experimental group (p = 0.51) and the control group (p = 0.87). The results showed that the effect of time was significant for the experimental group (F = 8.81, p = 0.001) but it was not significant for the controls (F = 0.45, p = 0.64).

The Bonferroni post hoc test was applied to find out where exactly the difference in levels of measurement lied, and the results demonstrated a 13.2% decrease in the post-test scores of the pain perception as compared to the pre-test scores which were statistically significant (p = 0.005). Post-test scores of the pain perception showed a 9.05% reduction compared to the pre-test scores (p = 0.01), but follow-up scores demonstrated a 4-point increase compared to the pre-test scores, which were not statistically significant (p = 0.6).

Independent sample t tests were used to compare pre-test scores of pain perception with follow-up and post-test scores. The results showed that compared to the control group, the mean pain perception scores at post-test (p = 0.02) and follow-up were reduced in the interventional group significantly (p = 0.01) (Table 2 and Fig. 2).

Pain Acceptance

To compare this variable between the study groups, a repeated-measures ANOVA was used. For this purpose, the assumption evaluated the equality of covariance matrices, and then the results of Box’s M test met the equality of covariance matrices (Box's M = 10.95, p = 0.12). The assumption of homogeneity of variance was met between different levels of measurement (p < 0.05). Mauchly’s test confirmed the assumption of sphericity (p = 0.51 and Mauchly’s W = 0.51). The results of the within-group tests indicated that the effect of time was significant (F = 6.48, p = 0.003, partial eta squared = 0.14) as was the effect of interaction between the time and groups (F = 12.49, p < 0.001, partial eta squared = 0.24) (Table 3).

As a result of the significant effect of time in both groups, a repeated-measures ANOVA for each group was used. Mauchly’s sphericity test indicated that the assumption of sphericity was met for both the groups of cases (p = 0.62) and control (p = 0.6). The results showed that the effect of time was significant for the case group (F = 16.30, p < 0.001, partial eta squared = 0.46) but it was not significant for the controls (F = 0.52, p = 0.64, partial eta squared = 0.03) (Table 3 and Fig. 3).

Fig. 3
figure 3

Comparison of mean score of pain acceptance between ACT group and control group in the pre-test, post-test, and follow-up phases

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According to Bonferroni post hoc test, the post-test scores of the pain acceptance demonstrated a 17.55% increase compared to the pre-test scores, which were statistically significant (p = 0.001). The post-test pain acceptance scores showed a 13.25% increase compared to the pre-test scores (p = 0.01), and follow-up scores demonstrated a 4.3% reduction compared to the pre-test scores which were not statistically significant (p = 0.51).

Independent sample t tests were used to compare the pre-test scores of pain acceptance with follow-up and post-test scores. The results showed that compared to the control group the mean pain acceptance scores at post-test (p = 0.02) and follow-up were reduced in the interventional group significantly (p = 0.01) (p < 0.001) (Table 2 and Fig. 2).

Discussion

Utilizing ACT as the treating approach, the current research aimed at studying the role of pain acceptance in pain perception reduction in patients with painful diabetic neuropathy whose pain was the main symptom. The results indicated that compared to the control group, the interventional group had significantly improved pain acceptance and a significant reduction in pain perception in the post-test phase. The results were repeated in the 3-month follow-up. This study is one of the first randomized controlled trials in the psychology field dedicated to painful diabetic neuropathy, and its literature review is sets out the first steps. The results are consistent with previous studies on the effectiveness of ACT on diseases associated with pain and focus on the acceptance component [38,39,40,41,42]; for example, in an investigation by Herbert et al., the effectiveness of ACT for chronic pain was studied. The results suggested that applying this treatment to patients with chronic pain could significantly lead to reduced pain severity and depression symptoms and increased chronic pain acceptance [43]. In another study, Scott et al. investigated the efficacy of an Internet-based acceptance and commitment therapy. The results indicated that the ACT could significantly reduce pain severity in patients with complex chronic pain [40].

The fundamental element of ACT for treating pain is experiential avoidance. Persons who choose experiential avoidance try to control or avoid pain instead of experiencing it. The primary model for ACT based on Hayes’ point of view suggests that trying to control or avoid pain is correlated with higher pain levels [44].

The first step in explaining increased pain acceptance uses the creative hopelessness concept. During the first sessions, the patient learns that trying to control or avoid pain does not reduce the pain and, instead, results in being involved in it [26]. Furthermore, self-as-context and cognitive defusion play a role in pain perception and adapting it. The patients learn that experiencing pain is not the same as their existence and totality [28, 45, 46].

As a result of ACT, the patients learn that there is a difference between one’s existential nature and their experiences, affects, feelings, and thoughts, and feeling the pain does not indicate a total weakness in their personality. Furthermore, the patients learn to be self-observers of experiencing pain, without judgment. Using techniques like the white room, they also learn to experience pain solely in the present moment, similar to other emotions like sadness, happiness, kindness, and anger without trying to reduce it. Various studies have indicated that this leads to increased pain tolerance and decreased pain perception [47, 48].

Finally, the patients learn to identify and clarify their values and act on them. In a study on ACT, Wetherell indicated that patients with chronic pain who mostly live according to their values are less likely to catastrophize pain and more likely to accept it [24].

This research indicated that emphasizing acceptance and living according to personal values despite the pain and using self-as-context and cognitive defusion techniques could significantly lower the pain perception and increase social and work functioning in the patients.

Future studies measuring concepts related to acceptance and pain tolerance are recommended in patients with PDN. These concepts include self-kindness and common humanity based on a mindful self-compassion approach. Moreover, in the current protocol, acceptance is the main emphasized component for the first three sessions; it is recommended that future investigations use mid-test to focus on acceptance solely without involving the other therapeutic components and measuring if it can predict the reduction of pain severity in the ACT model for pain in neuropathy. Moreover, according to van Laake-Geelen’s research in 2019, utilizing physical, behavioral techniques such as exercise therapy accompanied by ACT results in improved diabetic neuropathy pain management [49].

The limitations of the current research include using no measure of actual daily functioning, disability, and emotional functioning, utilizing self-report scales, reduction in sample size due to high dropout rate during screening regarding inclusion and exclusion criteria for neuropathy pain, low educability of the clinical sample due to the age range and being aged and not having an extended follow-up for examining the stability of pain acceptance on decreasing pain perception.

Conclusions

The results indicated that acceptance and commitment therapy could be used as a psychological intervention alongside pharmacotherapy to improve pain acceptance and reduce pain perception in patients with painful diabetic neuropathy.