Pain, psychosocial tests, pain sensitization and laparoscopic pelvic surgery

1 Introduction

Operative laparoscopy is a very common procedure undertaken for a wide variety of gynecological disorders [1]. While initially developed as diagnostic procedure it now is associated with minor (tubal ligation) and complex operative procedures (hysterectomy, pelvic floor reconstruction and extensive cancer surgery) [2], [3], [4]. The more common operative procedures for non-acute pain are directed to the diagnosis and treatment conditions of endometriosis, adhesions, pelvic inflammatory disease, and various ovarian disorders [5], [6], [7], [8].

Postsurgical chronic pain (PSCP) is being recognized as a common condition that requires improved approaches for a better understanding and treatment [9]. One of the proposed approaches is the use of both pain testing and psychological testing strategies. A recent study of the postoperative pain outcomes in several surgical conditions has emphasized the importance of pain sensitization as a predictor of clinical pain [10]. Recently a decision has been made to include chronic postsurgical pain (CPSP) in the new version of The International Classification of Diseases (ICD-11 that will be released in 2018) [11].

Pain sensitization can be defined as “Increased responsiveness of nociceptive neurons to their normal input, and/or recruitment of a response to normally sub-threshold inputs” [12]. Peripheral sensitization is considered to be increased responsiveness and reduced threshold of nociceptive neurons in the periphery while central sensitization is increased responsiveness of nociceptive neurons in the central nervous system to their normal or sub-threshold afferent input [12]. The subject has been extensively reviewed, recently in the transition from acute to chronic pain after surgery [10], [13]. Clinically, sensitization may only be inferred indirectly from measureable phenomena such as hyperalgesia or allodynia [12]. Pain sensitization influences the outcomes of surgery in a number of clinical situations [10], [14], [15], [16].

The detection of sensitization among women with chronic pelvic pain is established by the presence of allodynia and reduced pain thresholds in the dermatomes that supply the innervations to the pelvic structures. Among women with chronic pelvic pain, such sensitization has been shown to be frequent and detectable at the bedside and importantly can discriminate somatic from visceral disease [14]. Mechanosensory testing of women having hysterectomy indicated positive testing detected greater postoperative pain [17]. Pain sensitivity testing pre- and post-operatively predicted post-operative heat pain and pain with movement when tested 10 days after a laparoscopic tubal ligation [18]. In a cross sectional study of women with biopsy proven endometriosis, pelvic pain and control volunteers, and sensitization was common in those with pain whether or not they had endometriosis [15]. A prospective study of women with non-acute pain reported that pain sensitization as defined by the presence of allodynia, preoperative average pain and catastrophizing could predict the post-operative pain experience [19]. The surgery resulted in an overall reduction in pain associated with a reduction in allodynia, possibly due to the removal of a nociceptive focus as a source off the pain [19].

The current literature also supports psychosocial testing as part of the biopsychosocial framework of care for pelvic pain [20–22]. Consistently problematic areas that affect the outcome of surgery are depression, catastrophizing and disordered quality of life measures [23]. Psychosocial testing of women prospectively treated for endometriosis was shown to have a reduced probability of improvement in the presence of nulliparity and catastrophizing [24], [25]. Lower quality of life scores among women with chronic pelvic pain were shown to correlate directly with pain scores and there was no added impact of a diagnosis of endometriosis [26]. Women with chronic pelvic pain and endometriosis were commonly shown to have pain sensitization in association with elevated levels of anxiety and depression [20]. Anxiety and reduced coping skills have been shown to be associated with women with endometriosis with disorders of the hypothalamic pituitary adrenal axis [27]. Women with persistent pain after surgery for endometriosis were found to be younger and higher levels of catastrophizing [21].

The specific purpose of this study was to explore the change in pre- and post-operative psychosocial tests among women having operative laparoscopy for non-acute pain, determine if the tests correlated with one another and if these changes were sensitive to the presence of sensitization. Non-acute pain referred to women requiring surgical investigation or treatment that have not developed persistent chronic pain.

2 Methods

The study was done at Foothills Hospital, a regional tertiary center in a clinic specifically directed to the diagnosis and management of gynecological pain. The study was done between June 27, 2010 and June 30, 2012. The details of this study have been previously reported indicating the variables associated with the prediction of postoperative pain [19]. It was a prospective longitudinal cohort study comprising 16 women having tubal ligations for contraception without non-acute pain and 61 women having operative laparoscopies to evaluate and treat non-acute pain. Women were eligible to enter the study between the ages of 18 and 50 who either had requested a sterilization procedure or had sufficient pelvic pain to warrant investigation and treatment. Women with serious additional medical or psychological illnesses or pregnancy were excluded. All women were recruited and followed up by a study nurse assigned to the clinic. Follow-up at a 6 month clinic visit was arranged by the study nurse. Attempts to complete follow-up were undertaken by telephone, email and in person and where required the questionnaires were completed verbally on the telephone.

Women had psychosocial tests of distress (McGill Pain Score (SF-MPQ) [15], [16], the CES-D depression scale (CES-D) [28], the Pain Disability Index (PDI) [29] and the Pain Catastrophizing Scale (PCS) [30] and tests of sensitization (cutaneous allodynia) before and 6 months following surgery for non-acute pain. Average reported pain for the past week was recorded on a 0–10 numeric scale. The assessment of pain sensitization was based on the presence or absence of cutaneous allodynia on the lower abdomen [17], [20]. Briefly the test consists of a cotton tipped applicator drawn down the abdomen initially in the mid clavicular line while the patient is asked if there is a sudden change in the sensation or a painful experience. The area is tested bilaterally and the direction is modified so that principally the region of T 12 and L1 dermatomes are evaluated. This test has been shown to be significantly associated with the presence of previous or contemporaneous visceral pelvic disease [14]. A sample of 60 women with measurements before and after surgery would have >80% power to detect a medium effect size of 0.5 standard deviations of change in subjective pain level ratings, assuming α=0.05. For example, if the standard deviation of the difference in pain level was 3, then 60 women would allow us to detect a 1.5-point change in pain levels, with α=0.05 and power >0.80. A convenience sample of a second group of 16 women who underwent tubal ligation was included to explore whether laparoscopy induced a painful postoperative response in women without preoperative pain.

The study received renewal ethics approval from the University of Calgary Conjoint Medical Ethics Committee (REB15-1178 REN3). All subjects provided written informed consent after ethics approval was granted.

The differences in baseline scores between groups were compared using the Mann-Whitney U-test and 95% confidence intervals for the Hodges-Lehmann estimation of median differences were reported. Differences in change in scores from baseline to 6 months postoperatively were assessed using the paired t-test. The relationship of these tests in relation to themselves and to the average pain reported at baseline and change in scores of tests was assessed by Spearman and Pearson correlation coefficient analysis. The effect size of the difference in scores was calculated with Cohen’s d [31], [32]. Missing values were considered missing completely at random and were excluded from the analysis.

3 Results

The demographics of the subjects in the study have been previously reported [19]. The number of individuals with missing data for each of the tests is presented in the accompanying tables (Tables 1–3).

3.2 Surgery effects

Laparoscopic surgery in the entire cohort significantly reduced average pain (p<0.001) and all tests of psychosocial distress; CESD (p<0.001), PCS (p=0.001), PDI (p<0.001), SFMPQ (p<0.001) (Fig. 1). These differences were significant for all tests when the comparisons were done on women having surgery for non-acute pain. Of these women, 33 women, 43% of the entire cohort was found to be sensitized (Table 1). Women having laparoscopic surgery for non-acute pain had significantly greater average pain levels (median 5, IQR 3 vs. median 0.5, IQR 3.25) and rates of sensitization [31 (52.5%) vs. 2 (12.5%)] than women having surgery for a tubal ligation (p<0.001) (Table 1).

Fig. 1:

Comparison of pre- and postoperative average pain and psychosocial scores among all women having operative laparoscopic surgery. All tests differ at p<0.001 excepts PCS – p=0.001.

3.4 Sensitization effects

At baseline pain sensitization was associated with greater pain and distress scores in the entire cohort: average pain (p=0.004), CES-D (p=0.055), PCS (p=0.011), PDI (p=0.003) and SFMPQ (p=0.017) (Table 3). The pattern was similar for those having surgery for non-acute pain (Fig. 2).

Fig. 2:

Baseline psychosocial test scores of women having pelvic laparoscopic surgery: association with pain sensitization.

4 Discussion

This study indicated laparoscopic surgery involving visceral trauma resulted in a reduction in average reported pain and all tests of psychosocial tests. When the indication for surgery was non-acute pain the pattern of change was less dramatic; differences were significant for changes in average pain and PDI although the trend was similar for the other tests [32]. In terms of achieving minimally clinically significant changes, the results appeared to favor the PDI [15] while falling short for Pain Catastrophizing [16] and Short Form McGill Pain [28], [29] score. The subjects appeared to have sub-depression threshold values on the CES-D test [30].

There were significant correlations of baseline pain and psychological measures of distress pre-operatively. Women having surgery for pain had greater measures of distress than those having a tubal ligation indicating the importance of pre-operative pain in assessing psychological distress [33].

The rate of pain sensitization was greater among those having surgery for non-acute visceral source of pain than women having tubal ligations [34]. The presence of sensitization was associated with trends to greater baseline and 6 month postoperative changes in average pain and measures of psychological distress. These were statistically significant when the entire cohort was considered. The close correlation of average pain and tests of psychological distress continued after surgery as has been reported in other postoperative studies [21], [35].

The objective of the surgery in women with non-acute pain was to reduce visceral pain. This differs from much of the literature on CPSP in several ways. First, the target is visceral tissues. Second, the criteria originally proposed by Macrae, as recently modified for ICD-11 still excludes of other possible causes for the pain [11], [36]. This criterion is difficult to meet in relation to gynecological literature as many women suffer from recurrent disease processes, particularly endometriosis [19], [37]. Further, women can undergo surgery for conditions that have initiated pain sensitization that remains after the operation has been undertaken.

The limitations of the study include the modest sample size and missing data due to loss to follow-up at 6 months or incomplete questionnaires at baseline or 6 months. As this was exploratory secondary analysis of existing data [19], the sample size was not powered to compare the tubal ligation and non-acute pain group nor the impact of sensitization within each group. Although missing data was treated as missing completely at random, we had no way of knowing whether this was truly the case.

In summary, psychosocial testing correlated well with reductions in average pain pre- and postoperatively. Women having surgery for pre-existing pain had greater degrees of distress than those having surgery for non-acute pain. When all subjects were considered, baseline and postoperative average pain correlated significantly with tests of psychosocial distress. Also when all subjects were considered, women with pain sensitization had significant decreases in average pain and pain disability although all tests showed a similar trend. Incorporation of these tests in the pre- and postoperative evaluation of women having laparoscopic surgery provide a broader understanding of the woman’s pain experience.