Comparing pain sensitivity and the nociceptive flexion reflex threshold across the mid-follicular and late-luteal menstrual phases in healthy women

Efficacy and Pain Tolerance of Alexandrite Laser Hair Removal at Different Stages of the Menstrual Cycle

BACKGROUND

Several different parameters play a role in the transition of hair follicles to the anagen phase, with the role of androgens, progesterone, and estrogen hormones and receptors being significant.

OBJECTIVES

The effectiveness of laser hair removal (LHR) and pain tolerance during procedure were investigated during 3 different phases of the menstrual cycle.

METHODS

Forty-eight axillae were randomly divided into 3 groups: menstruation, ovulation, and luteal. Three laser sessions were performed on each axilla at a 1-month interval. Blood hormone levels were measured in the patients. An alexandrite laser was applied during LHR sessions. Before each LHR session and 1 month after the third session, hair follicles in 4-cm2 areas in the center of the axillae were counted. Patients self-assessed the pain they felt during the laser application in each session with a visual pain scale.

RESULTS

The average values for hair counting in the groups were as follows (M, menstruation; O, ovulation; L, luteinization): M0 = 47.6, M1 = 27.4, M2 = 16.1, M3 = 9.9; O0 = 41.8, O1 = 21.1, O2 = 13.8, O3 = 8.6; and L0 = 49.4, L1 = 27.1, L2 = 15.1, L3 = 9.8. The average values on the visual analog scale scores in the groups were: M1 = 3.94, M2 = 3.06, M3 = 1.94; O1 = 3.50, O2 = 3.06, O3 = 1.69; and L1 = 3.63, L2 = 2.50, L3 = 1.56. Statistical analysis was conducted with Tukey post hoc analysis after analysis of variance.

CONCLUSIONS

The results of LHR are not affected by changes in hormone levels during the menstrual cycle in females. Although not statistically significant, it has been observed that pain tolerance during laser application is lower during the menstruation cycle.

LEVEL OF EVIDENCE: 3

Healthy women show more experimentally induced central sensitization compared with men

ABSTRACT

Women more often experience chronic pain conditions than men. Central sensitization (CS) is one key mechanism in chronic pain that can differ between the sexes. It is unknown whether CS processes are already more pronounced in healthy women than in men. In 66 subjects (33 women), a thermal CS induction protocol was applied to the dorsum of one foot and a sham protocol to the other. Spatial extent [cm 2 ] of secondary mechanical hyperalgesia (SMH) and dynamic mechanical allodynia were assessed as subjective CS proxy measures, relying on verbal feedback. Changes in nociceptive withdrawal reflex magnitude (NWR-M) and response rate (NWR-RR) recorded through surface electromyography at the biceps and rectus femoris muscles were used as objective CS proxies. The effect of the CS induction protocol on SMH was higher in women than in men (effect size 2.11 vs 1.68). Nociceptive withdrawal reflex magnitude results were statistically meaningful for women (effect size 0.31-0.36) but not for men (effect size 0.12-0.29). Differences between men and women were not meaningful. Nociceptive withdrawal reflex response rate at the rectus femoris increased in women after CS induction and was statistically different from NWR-RR in men (median differences of 13.7 and 8.4% for 120 and 140% reflex threshold current). The objective CS proxy differences indicate that dorsal horn CS processes are more pronounced in healthy women. The even larger sex differences in subjective CS proxies potentially reflect greater supraspinal influence in women. This study shows that sex differences are present in experimentally induced CS in healthy subjects, which might contribute to women's vulnerability for chronic pain.

Sex hormone mediated change on flexion reflex

It has been shown that estrogen and progesterone receptors are expressed in the spinal cord; therefore, fluctuation in their concentrations may affect the spinal network and modulate the control of movement. Herein, we assessed the neuro-modulatory effect of sex hormones on the polysynaptic spinal network by using a flexion reflex network as a model system. Twenty-four healthy eumenorrheic women (age 21-37 years) were tested every other day for one menstrual cycle. Serum estradiol and progesterone were acquired at the time of testing. The flexion reflex of the tibialis anterior was elicited by sending an innocuous electrical stimulus directly to the posterior tibial nerve or plantar cutaneous afferent. Analyses were performed for each menstrual cycle phase: the follicular phase and the luteal phase. Increases in estradiol or progesterone concentrations were not associated with reflex duration or root mean squared (RMS) amplitude in either the follicular or luteal phases. In the luteal phase, an increase in the estradiol concentration was associated with a longer latency of the reflex (b = 0.23, p = 0.038). The estradiol × progesterone interaction was found towards significance (b = -0.017, p = 0.081). These results highlight the potential synergistic effect of estradiol and progesterone and may provide indirect confirmatory evidence of the observed modulatory effect.

Menstrual migraine is caused by estrogen withdrawal: revisiting the evidence

OBJECTIVE

To explore and critically appraise the evidence supporting the role of estrogen withdrawal in menstrual migraine.

MAIN BODY

Menstrual migraine, impacting about 6% of reproductive-age women, manifests as migraine attacks closely related to the menstrual cycle. The estrogen withdrawal hypothesis posits that the premenstrual drop in estrogen levels serves as a trigger of migraine attacks. Despite its wide acceptance, the current body of evidence supporting this hypothesis remains limited, warranting further validation. Estrogen is believed to exert a modulatory effect on pain, particularly within the trigeminovascular system - the anatomic and physiologic substrate of migraine pathogenesis. Nevertheless, existing studies are limited by methodologic inconsistencies, small sample sizes, and variable case definitions, precluding definitive conclusions. To improve our understanding of menstrual migraine, future research should concentrate on untangling the intricate interplay between estrogen, the trigeminovascular system, and migraine itself. This necessitates the use of robust methods, larger sample sizes, and standardized case definitions to surmount the limitations encountered in previous investigations.

CONCLUSION

Further research is thus needed to ascertain the involvement of estrogen withdrawal in menstrual migraine and advance the development of effective management strategies to address unmet treatment needs.

Changes in sex hormones and their interactions are related to pain perception between different menstrual subphases

Whether sex hormones are related to pain perception across the menstrual cycle is unclear. We examined changes in experimental pain perception in healthy young females between the early to midfollicular subphase (emF) and the midluteal subphase (mL) and explored the role of sex hormones. Sixty-six participants were involved in the study. We tested pressure pain, cold pain, ischemic pain, and needle pain, while at the same time we measured sex hormones levels in two menstrual subphases. Only the right ulna pressure test showed a significant reduction in pain threshold (PPTh3) during the mL. The absolute change of PPTh3 (PPTh3mL - PPTh3emF) was related to the absolute change of prolactin. The relative change of the range of pain tolerance for pressure pain of the right ulna (RPT3rc) was related to the relative change of progesterone (Prc) and estradiol (E2rc) levels, and the interaction effects showed that at Prc ≤ 30, E2rc was positively correlated with RPT3rc. The same, the relative change of pressure pain tolerance of the pulp of the middle finger on the right hand (PPTo4rc) was related to E2rc and Prc, and the results of the interaction between E2rc and Prc suggest that when E2rc is ≤0.8, Prc is positively correlated with PPTo4rc. Two different formulas were applied in this study and showed inconsistent results. Most pain tests showed no difference between the two subphases of the menstrual cycle. Only the relative changes of the PPTo4 and RPT3 are related to the E2rc and Prc, respectively, between menstrual subphases in an interactive way in healthy young women.

Myofascial Pain Syndrome in Women with Primary Dysmenorrhea: A Case-Control Study

There is limited information on myofascial trigger points (MTrPs) and specific symptoms of chronic pelvic pain and, more specifically, dysmenorrhea. The objective of this study was to determine whether patients suffering from primary dysmenorrhea present alterations in mechanosensitivity and pain patterns, and greater presence of MTrPs in the abdominal and pelvic floor muscles. A case-control study was carried out with a total sample of 84 participants distributed based on primary dysmenorrhea and contraceptive treatment. The sample was divided into four groups each comprising 21 women. Data on pain, quality of life, and productivity and work absenteeism were collected; three assessments were made in different phases of the menstrual cycle, to report data on pressure pain threshold, MTrP presence, and referred pain areas. One-way ANOVA tests showed statistically significant differences (p < 0.01) between the groups, for the Physical Health domain and the total score of the SF-12 questionnaire, and for all the domains of the McGill questionnaire; but no significant differences were found in the data from the WPAI-GH questionnaire. Statistically significant data (p < 0.01) were found for mechanosensitivity in the abdominal area and limbs, but not for the lumbar assessment, within the group, with very few significant intergroup differences. The frequency of active MTrPs is higher in the groups of women with primary dysmenorrhea and during the menstrual phase, with the prevalence of myofascial trigger points of the iliococcygeus muscle being especially high in all examination groups (>50%) and higher than 70% in women with primary dysmenorrhea, in the menstrual phase, and the internal obturator muscle (100%) in the menstrual phase. Referred pain areas of the pelvic floor muscles increase in women with primary dysmenorrhea.

Hypohydration but not Menstrual Phase Influences Pain Perception in Healthy Women

Chronic pain is a pervasive health problem and is associated with tremendous socioeconomic costs. However, current pain treatments are often ineffective due, in part, to the multi-factorial nature of pain. Mild hypohydration was shown to increase experimental pain sensitivity in men, but whether this also occurs in women has not been examined. Fluctuations in ovarian hormones (i.e., 17ß-oestradiol and progesterone) throughout the menstrual cycle may influence a woman's pain sensitivity, as well as hydration levels, suggesting possible interactions between hypohydration and menstrual phase on pain. We investigated the effects of mild hypohydration (HYPO, 24 hr of fluid restriction) on ischaemic pain sensitivity in 14 eumenorrheic women during the early follicular (EF) and mid-luteal (ML) phases of their menstrual cycle. We also examined whether acute water ingestion could reverse the negative effects of hypohydration. Elevated serum osmolality, plasma copeptin, and urine specific gravity indicated mild hypohydration. Compared to euhydration, HYPO reduced pain tolerance (by 34 ± 46 s; P = 0.02, ηp2 = 0.37) and increased ratings of pain intensity (by 0.7 ± 0.7 cm; P = 0.004; ηp2 = 0.55) and unpleasantness (by 0.7 ± 0.9 cm; P = 0.02; ηp2 = 0.40); these results were not influenced by menstrual phase. Water ingestion reduced thirst perception (Visual Analogue Scale, by 2.3 ± 0.9 cm; P < 0.001, ηp2 = 0.88) but did not reduce pain sensitivity. Therefore, hypohydration increases pain sensitivity in women with no influence of menstrual phase.

Can Injuries Have a Lasting Effect on the Perception of Pain in Young, Healthy Women and Men?

BACKGROUND

Pain is a characteristic, unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is a subjective sensation, modulated by many factors such as age, sex, emotional state, national origin, or physical activity. Moreover, it is closely associated with intense physical activity, injuries, and traumas, which can significantly modulate pain tolerance.

HYPOTHESIS

We postulate that there are correlations between past injuries, physical activity, and intensity of pain perception (pain threshold and pain tolerance) in a population of healthy men and women.

STUDY DESIGN

Retrospective cohort study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 302 participants aged 18 to 32 years were included. The participants were divided into 2 groups (active and inactive individuals), in accordance with the scope of physical activity they had indicated. The test of pressure pain threshold and pressure pain tolerance was performed using an algometer.

RESULTS

Active women achieved significantly higher pain threshold and pain tolerance values in all measurements on the upper limb (except for the pain threshold on the left hand) compared with inactive women. In mediation analysis, the effect of injury remained significant only for the pressure pain tolerance in the dominant arm and the left hand in the female group. In the case of men, there were no significant differences in all measurements in view of the threshold and tolerance for pain between the groups of active and inactive and between men with injuries and without injuries.

CONCLUSION

Intense, regular physical activity is a factor modulating the perception of pain. This was demonstrated as lowered sensitivity to pain stimuli in a population of healthy women.

CLINICAL RELEVANCE

Injuries should be treated as an important factor modulating the perception of pain. We recommend detailed monitoring of injuries during treatment and control of pain sensation.

Effect of different factors on patient perception of surgical discomfort in third molar surgery

The aim of this study was to evaluate patient perception of surgical discomfort in third molar surgery and the association with clinical variables and polymorphisms associated with the FKBP5, SLC6A4, and COMT genes. This cross-sectional observational study was carried out on 196 participants aged between 18 and 64 years at the Federal University of Paraná in 11 months. The intensity of surgical discomfort was assessed using the QCirDental questionnaire. Data on surgical and individual procedures were also cataloged. The oral health related quality of life was assessed by the Oral Health Impact Profile questionnaire (OHIP-14). The DNA sample was obtained from cells of the oral mucosa. Five markers of the FKBP5, SLC6A4, and COMT genes were genotyped. The data were submitted to statistical analysis with a significance level of 5%. Women reported greater intensity of discomfort associated with third molar surgery compared to men (p = 0.001). In the recessive model, the AA genotype of the rs3800373 marker was associated with greater surgical discomfort (p = 0.026). Therefore, women and individuals of the AA genotype for the rs3800373 marker in the FKBP5 gene reported greater surgical discomfort associated with third molar surgery.

Effects of Conditioned Pain Modulation on the Nociceptive Flexion Reflex in Healthy People: A Systematic Review

OBJECTIVES

The nociceptive flexion reflex (NFR) is a spinal reflex induced by painful stimuli resulting in a withdrawal response. Research has shown that the NFR is inhibited through endogenous pain inhibitory mechanisms, which can be assessed by conditioned pain modulation (CPM) paradigms. Although accumulating research suggests that the NFR can be affected by CPM, no clear overview of the current evidence exists. Therefore, the present review aimed at providing such a synthesis of the literature. In addition, the influence of personal factors on the CPM of the NFR was investigated.

MATERIALS AND METHODS

A systematic review was performed and reported following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Five electronic databases were searched to identify relevant articles. Retrieved articles were screened on eligibility using predefined inclusion criteria. Risk of bias was investigated according to the modified Newcastle-Ottawa Scale. Levels of evidence and strength of conclusion were assigned following the guidelines of the Dutch Institute for Healthcare Improvement.

RESULTS

Forty articles were included. There is some evidence that CPM produced by thermal or mechanical stimuli induces inhibitory effects on the NFR. However, inconclusive evidence exists with regard to the effect of electrical conditioning stimuli. While several personal factors do not affect CPM of the NFR, increased cognitive interference is associated with reduced NFR inhibition.

DISCUSSION

The present review demonstrates that certain types of nociceptive conditioning stimuli have the potential to depress, at the spinal level, nociceptive stimuli elicited from distant body regions. Although CPM of the NFR seems to be robust to the influence of several personal factors, it can be affected by cognitive influences.

Can self-pain sensitivity quantify empathy for others' pain?

Empathy is essential for the survival of social species. In many studies, especially those with animal models, empathy for pain was evaluated by the modulation of pain sensitivity. However, the relationship between pain sensitivity and empathy for pain is not well established. Here, by performing two experiments, we aimed to investigate their relationship at both behavioral and electrophysiological levels. In Experiment 1, we characterized individual pain sensitivity using pain threshold and tolerance in a cold pressor test, self-report empathy using Interpersonal Reactivity Index, and pain-related psychological factors, including pain-related anxiety, depression, pain catastrophizing, and pain-related fear, using well-validated questionnaires. We observed that pain sensitivity was positively correlated with emotional empathy, and their relationship was mediated by pain-related anxiety, pain catastrophizing, and pain-related fear. In Experiment 2, we quantified empathy for pain using pain intensity and unpleasantness as well as event-related potentials (ERPs) in an empathy for pain task. Positive correlations were observed between pain sensitivity and psychophysiological empathic responses (i.e., the P3 component and the late positive potential in ERPs), and their relationship was mediated by pain-related fear. These results suggested that being influenced by some pain-related psychological factors, individuals with higher pain sensitivity tended to have stronger empathy for pain, manifested as stronger emotional reactions to others' pain. Our results indicated that the conventional strategy of using pain sensitivity to quantify empathy should be treated with caution, as their relationship could be disturbed by experimental manipulations or pathological modulations that could influence individual emotional states or cognitive processes.

Chronic Fatigue, Physical Impairments and Quality of Life in Women with Endometriosis: A Case-Control Study

AIM

To explore endometriosis-related fatigue (ERF), health-related fitness, sleep quality, and health-related quality of life (HRQoL) in women with endometriosis in comparison with matched controls.

METHODS

Twenty-five affected women and twenty-five age and height-matched women without endometriosis were included. ERF was assessed through the Piper Fatigue Scale; health-related fitness was assessed through the Schöber, flamingo, and 6-min walking tests and dynamometry; and body composition was assessed through impedanciometry. Self-perceived physical fitness, sleep quality, and HRQoL were assessed through the International Fitness Scale, the Pittsburgh Sleep Quality Index, and the 12-item Short Form Health Survey, respectively.

RESULTS

Affected women exhibited higher levels of ERF than controls, increased fat mass, and physical deconditioning (reduced back strength, lumbar flexibility, body balance, and functional capacity, p-values < 0.050). Moreover, cases also had poorer perceived physical fitness, sleep quality, and HRQoL (p-value < 0.050). Finally, we observed deteriorated health-related fitness, sleep quality, and HRQoL in those women with endometriosis with higher levels of ERF.

CONCLUSIONS

This study constitutes the first evidence that women with endometriosis describe a generalized physical deconditioning, even more pronounced in affected women with higher levels of ERF. Further studies assessing the efficacy of rehabilitation interventions to face these physical impairments in women with endometriosis are warranted.

Sex differences in measures of central sensitization and pain sensitivity to experimental sleep disruption: implications for sex differences in chronic pain

Study Objectives

Females demonstrate heightened central sensitization (CS), a risk factor for chronic pain characterized by enhanced responsivity of central nervous system nociceptors to normal or subthreshold input. Sleep disruption increases pain sensitivity, but sex has rarely been evaluated as a moderator and few experiments have measured CS. We evaluated whether two nights of sleep disruption alter CS measures of secondary hyperalgesia and mechanical temporal summation in a sex-dependent manner. We also evaluated differences in measures of pain sensitivity.

Methods

Seventy-nine healthy adults (female n = 46) participated in a randomized crossover experiment comparing two consecutive nights of eight pseudorandomly distributed forced awakenings (FA [-200 min sleep time]) against two nights of undisturbed sleep (US). We conducted sensory testing the mornings following Night 2; the heat-capsaicin pain model was used to induce secondary hyperalgesia.

Results

FA reduced total sleep time (REM and NREM Stage 3) more profoundly in males. We observed divergent, sex-dependent effects of FA on secondary hyperalgesia and temporal summation. FA significantly increased secondary hyperalgesia in males and significantly increased temporal summation in females. Sex differences were not attributable to differential sleep loss in males. FA also significantly reduced heat-pain threshold and cold pressor pain tolerance, independently of sex.

Conclusions

Sleep disruption enhances different pain facilitatory measures of CS in males and females suggesting that sleep disturbance may increase risk for chronic pain in males and females via distinct pathways. Findings have implications for understanding sex differences in chronic pain and investigating sleep in chronic pain prevention efforts.

Influence of the Menstrual Cycle Phase on Pain Perception and Analgesic Requirements in Young Women Undergoing Gynecological Laparoscopy

CONTEXT

The influence of the gonadal hormones on some aspects of the human physiology has been studied with uncertain results. Still a confusion exists in relation to the real effects of the female hormones on the perception of pain. The existing data refer mainly to experimental studies and have provided results not always useful in the clinical practice.

DATA SOURCE

This study was designed to detect whether there are differences in the perception of the postoperative pain in women, during two clearly defined phases of hormonal asset: luteal and follicular phases.

CONCLUSION

The results of this study have demonstrated that in postoperative female patients pain is perceived significantly more in the luteal phase of the menstrual period, than in the follicular phase. This could suggest that female in child-bearing age should be scheduled for elective surgery preferentially during the follicular phase, unless differently necessary. It would guarantee a more comfortable postoperative period, with reduced necessity of analgesics.

Evaluation the relationship between serum progesterone level and pain perception after cesarean delivery

Introduction: Cesarean delivery is the most common surgery in obstetrics, and pain relief after cesarean section is an important concern for obstetricians and their patients. Objective: The aim of this study was to evaluate the relationship between serum progesterone level and pain perception after cesarean delivery. Method: The study was performed as a prospective cohort study on 166 pregnant women who were candidates for elective cesarean delivery due to previous cesarean section. Before surgery, serum progesterone level was measured. Pain score of women was evaluated 4, 8, 12, and 24 h after surgery using visual analog scale (VAS) score, and correlation between progesterone level and pain was evaluated. Results: The median value of serum progesterone was 119.45 ng/ml. Mean pain score in hours 4, 8, 12, and 24 were 6.80 ± 2.11, 5.31 ± 1.48, 3.89 ± 1.68, and 2.30 ± 1.26, respectively. The women were divided according to mean progesterone level of 119.45 ng/ml into two groups of high progesterone level (≥119.45) and low progesterone level (<119.45), and the pain score was evaluated in different times (hour 4, 8, 12, and 24) for both levels of progesterone. The mean pain score in the 4, 8, 12, and 24 h were significantly lower in high progesterone group (progesterone level ≥119.45). The number of women with low pain score (less than five) in hours 12 and 24 was significantly higher in high progesterone level group. With increasing BMI, progesterone level was lower and women with higher BMI, had a higher pain score in hours 4, 8, 12, and 24, while women with lower BMI had a lower pain score during the same hours. (p = .004, r = 0.223; p = .004, r = 0.223; p = .039, r = 0.160; and p = .007, r = 0.207). Progesterone level and BMI (p = .025, r = - 0.174), and progesterone level and pain score in hours 4, 8, 12, and 24 (p = .000, r = - 0.324; p = .000, r = - 0.474; p = .000, r = - 0.329; and p = .000, r = - 0.417, respectively) showed a negative significant correlation. Putting three variables of age, gestational age, and BMI in a multiple regression model, progesterone level showed significant negative correlation with the pain score in hour 4 (p = .000, r = - 0.305), hour 8 (p = .000, r = - 0.461), hour 12 (p = .000, r = - 0.328), and hour 24 (p = .000, r = - 0.409). Conclusions: Serum progesterone level showed a negative correlation with the pain score after cesarean section.

[The influence of the menstrual cycle on acute and persistent pain after laparoscopic cholecystectomy]

BACKGROUND AND OBJECTIVES

Fluctuations of female sex hormones during menstrual cycle influence pain perception. Endogenous pain inhibition is impaired in follicular phase of menstrual cycle. We tested the primary hypothesis that the women having surgery during their follicular phase have more acute pain and require higher opioids than those in the luteal phase, and secondarily we tested that women who have surgery during their follicular phase have more incisional pain at 3 month postoperatively.

METHODS

127 adult females having laparoscopic cholecystectomy were randomized to have surgery during the luteal or follicular phase of their menstrual cycle. Standardized anesthesia and pain management regimen was given to all patients. Pain and analgesic consumption were evaluated in post-anesthesia care unit and every 4h in the first 24h. Adverse effects were questioned every 4h. Time to oral intake and ambulation were recorded. Post-surgical pain, hospital anxiety, depression scale, SF-12 questionnaire were evaluated at 1 and 3 month visits.

RESULTS

There was no difference in acute pain scores and analgesic consumption through the 24h period, Visual Analog Scale at 24h was 1.5±1.5cm for follicular group 1.4±1.7cm for luteal group (p=0.57). Persistent postoperative pain was significantly more common one and at three month, with an incidence was 33% and 32% in the patients at follicular phase versus 16% and 12% at luteal phase, respectively. The Visual Analog Scale at one and at three month was 1.6±0.7cm and 1.8±0.8cm for follicular group and 2.7±1.3cm and 2.9±1.7cm in the luteal group (p=0.02), respectively. There were no significant differences between the groups with respect to anxiety and depression, SF-12 scores at either time. Nausea was more common in follicular-phase group (p=0.01) and oral feeding time was shorter in follicular phase (5.9±0.9h) than in luteal phase (6.8±1.9h, p=0.02).

CONCLUSIONS

Although persistent postoperative pain was significantly more common one and three months after surgery the magnitude of the pain was low. Our results do not support scheduling operations to target particular phases of the menstrual cycle.

Effect of Age, Sex and Gender on Pain Sensitivity: A Narrative Review

Introduction:

An increasing body of literature on sex and gender differences in pain sensitivity has been accumulated in recent years. There is also evidence from epidemiological research that painful conditions are more prevalent in older people. The aim of this narrative review is to critically appraise the relevant literature investigating the presence of age and sex differences in clinical and experimental pain conditions.

Methods:

A scoping search of the literature identifying relevant peer reviewed articles was conducted on May 2016. Information and evidence from the key articles were narratively described and data was quantitatively synthesised to identify gaps of knowledge in the research literature concerning age and sex differences in pain responses.

Results:

This critical appraisal of the literature suggests that the results of the experimental and clinical studies regarding age and sex differences in pain contain some contradictions as far as age differences in pain are concerned. While data from the clinical studies are more consistent and seem to point towards the fact that chronic pain prevalence increases in the elderly findings from the experimental studies on the other hand were inconsistent, with pain threshold increasing with age in some studies and decreasing with age in others.

Conclusion:

There is a need for further research using the latest advanced quantitative sensory testing protocols to measure the function of small nerve fibres that are involved in nociception and pain sensitivity across the human life span.

Implications:

Findings from these studies should feed into and inform evidence emerging from other types of studies (e.g. brain imaging technique and psychometrics) suggesting that pain in the older humans may have unique characteristics that affect how old patients respond to intervention.

New roles for neuronal estrogen receptors

Estrogens encompass steroid hormones which display physiological roles not only in the female reproductive system but also in other organ systems of non-reproductive controls, including the peripheral and central nervous systems. Traditionally, estrogen signals in neurons through a "genomic pathway": binding to estrogen receptors (ERs) which then interact with nuclear estrogen response elements to initiate transcription. This effect is usually delayed at onset (within several hours to days) and prolonged in duration. In addition to these classical ERs, recent data suggest that other ERs function through pregenomic signaling pathways. Estrogen's pregenomic pathways cause intracellular changes within seconds to minutes and go through a novel, 7-transmembrane spanning G protein-coupled receptor (GPER, formerly known as GPR30). In this review, we will briefly cover the cellular and molecular mechanisms of GPER and then discuss newly discovered roles of GPER in cognition, depression, homeostasis, pain processing, and other associated neuronal functions.

Natural variation in testosterone is associated with hypoalgesia in healthy women

OBJECTIVE

Sex differences in pain are well established, with women reporting greater incidence of clinical pain and heightened responsivity to experimental pain stimuli relative to men. Sex hormones (ie, estrogens, progestins, androgens) could contribute to extant differences in pain sensitivity between men and women. Despite this, there has been limited experimental research assessing the relationship between pain and sex hormones. The purpose of this study was to extend previous research and examine the association between sex hormones and nociceptive processing in healthy women.

MATERIALS AND METHODS

A total of 40 healthy women were tested during the mid-follicular, ovulatory, and late-luteal phases of the menstrual cycle (testing order counterbalanced). Salivary estradiol, progesterone, and testosterone were collected at each testing session and pain was examined from electrocutaneous threshold/tolerance, ischemia threshold/tolerance, and McGill Pain Questionnaire-Short Form ratings of noxious stimuli. Nociceptive flexion reflex threshold was assessed as a measure of spinal nociception.

RESULTS

Overall, there were no significant menstrual phase-related differences in pain outcomes. Nonetheless, variability in testosterone (and to a lesser degree estradiol) was associated with pain; testosterone was antinociceptive, whereas estradiol was pronociceptive. No hormone was associated with nociceptive flexion reflex threshold.

DISCUSSION

Although future research is needed to replicate and extend these findings to clinical populations (ie, chronic pain, premenstrual dysphoric disorder), results from the present study indicate that menstrual phase-related changes in sex hormones have minimal influence on experimental pain. However, individual differences in testosterone may play a protective role against pain in healthy women.

Experimenter Effects on Pain Reporting in Women Vary across the Menstrual Cycle

Background. Separate lines of research have shown that menstrual cycling and contextual factors such as the gender of research personnel influence experimental pain reporting. Objectives. This study examines how brief, procedural interactions with female and male experimenters can affect experimentally reported pain (cold pressor task, CPT) across the menstrual cycle. Methods. Based on the menstrual calendars 94 naturally cycling women and 38 women using hormonal contraceptives (M age = 19.83,  SD = 3.09) were assigned to low and high fertility groups. This assignment was based on estimates of their probability of conception given their current cycle day. Experimenters (12 males, 7 females) engaged in minimal procedural interactions with participants before the CPT was performed in solitude. Results. Naturally cycling women in the high fertility group showed significantly higher pain tolerance (81 sec, d = .79) following interactions with a male but not a female experimenter. Differences were not found for women in the low fertility or contraceptive groups. Discussion. The findings illustrate that menstrual functioning moderates the effect that experimenter gender has on pain reporting in women. Conclusion. These findings have implications for standardizing pain measurement protocols and understanding how basic biopsychosocial mechanisms (e.g., person-perception systems) can modulate pain experiences.

The relationship between serum progesterone concentration and anesthetic and analgesic requirements: a prospective observational study of parturients undergoing cesarean delivery

BACKGROUND

In clinical practice, pregnant women have lower anesthetic requirements for general anesthesia than nonpregnant women. Although the hormonal changes such as progesterone associated with pregnancy may affect the minimum alveolar concentration of volatile anesthetics, the relationship between the anesthetic or analgesic requirements and progesterone level in full-term women has not been studied. In this study, we attempted to identify relationships between anesthetic or analgesic requirements and maternal serum concentrations of progesterone.

METHODS

We studied 100 parturients >36 weeks' gestation who were scheduled for planned cesarean delivery under general anesthesia. Venous blood was collected to measure the maternal progesterone concentration. Anesthesia was induced with 4 to 5 mg/kg thiopental and 0.8 mg/kg rocuronium. During anesthetic maintenance, sevoflurane 0.5% to 2.0% and nitrous oxide 50% in oxygen were titrated based on arterial blood pressure, heart rate, and bispectral index value. Vital signs, bispectral index, end-tidal sevoflurane concentration, and sevoflurane consumption per hour were recorded. Visual analog scale pain scores and cumulative analgesic consumption were recorded at 2, 24, and 48 hours postoperatively.

RESULTS

The mean serum progesterone concentration was 128.2 ± 83.0 ng/mL. There was a significant negative correlation between sevoflurane consumption per hour and serum progesterone concentration (Pearson correlation r = -0.26; 95% confidence interval, -0.44 to -0.05, P = 0.01). Cumulative analgesic consumption at postoperative hours 2 (r = -0.20, P = 0.05), 24 (r = -0.25, P = 0.02), and 48 (r = -0.28, P = 0.01) were correlated inversely with serum progesterone concentration. Women with high progesterone levels (higher than the median value) had lower sevoflurane consumption per hour (P = 0.02) and 48-hour postoperative cumulative analgesic consumption (P = 0.02) than women with low (below the median value) levels.

CONCLUSIONS

The decreased anesthetic and analgesic requirements of near full-term parturients might partially depend on serum progesterone concentration.

Affective disturbance associated with premenstrual dysphoric disorder does not disrupt emotional modulation of pain and spinal nociception

In healthy individuals, emotions modulate pain and spinal nociception according to a valence linear trend (ie, pain/nociception is highest during negative emotions and lowest during positive emotions). However, emerging evidence suggests that emotional modulation of pain (but not spinal nociception) is disrupted in fibromyalgia and disorders associated with chronic pain risk (eg, major depression, insomnia). The present study attempted to extend this work and to examine whether women with premenstrual dysphoric disorder (PMDD), a cyclical syndrome associated with debilitating affective symptoms during the late-luteal (premenstrual) phase of the menstrual cycle, is also associated with disrupted emotional modulation of pain. To do so, an affective picture-viewing procedure was used to study emotional modulation of pain and spinal nociception in 14 women with PMDD and 14 control women during mid-follicular, ovulatory, and late-luteal phases of the menstrual cycle (verified by salivary hormone levels and luteinizing hormone tests). At each phase, mutilation, neutral, and erotic pictures were presented to manipulate emotion. During picture viewing, suprathreshold electrocutaneous stimuli were presented to evoke pain and the nociceptive flexion reflex (NFR; a physiological measure of spinal nociception). Statistically powerful linear mixed model analyses confirmed that pictures evoked the intended emotional states in both groups across all menstrual phases. Furthermore, emotion modulated pain and NFR according to a valence linear trend in both groups and across all menstrual phases. Thus, PMDD-related affective disturbance is not associated with a failure to emotionally modulate pain, suggesting that PMDD does not share this pain phenotype with major depression, insomnia, and fibromyalgia.

Fluctuating experimental pain sensitivities across the menstrual cycle are contingent on women's romantic relationship status

We explored the social-signaling hypothesis that variability in exogenous pain sensitivities across the menstrual cycle is moderated by women's current romantic relationship status and hence the availability of a solicitous social partner for expressing pain behaviors in regular, isochronal ways. In two studies, we used the menstrual calendars of healthy women to provide a detailed approximation of the women's probability of conception based on their current cycle-day, along with relationship status, and cold pressor pain and ischemic pain sensitivities, respectively. In the first study (n = 135; 18-46 yrs., Mage = 23 yrs., 50% natural cycling), we found that naturally-cycling, pair-bonded women showed a positive correlation between the probability of conception and ischemic pain intensity (r = .45), associations not found for single women or hormonal contraceptive-users. A second study (n = 107; 19-29 yrs., Mage = 20 yrs., 56% natural cycling) showed a similar association between greater conception risk and higher cold-pressor pain intensity in naturally-cycling, pair-bonded women only (r = .63). The findings show that variability in exogenous pain sensitivities across different fertility phases of the menstrual cycle is contingent on basic elements of women's social environment and inversely correspond to variability in naturally occurring, perimenstrual symptoms. These findings have wide-ranging implications for: a) standardizing pain measurement protocols; b) understanding basic biopsychosocial pain-related processes; c) addressing clinical pain experiences in women; and d) understanding how pain influences, and is influenced by, social relationships.

Mechanical pain sensitivity and the severity of chronic neck pain and disability are not modulated across the menstrual cycle

Despite the high prevalence of neck pain among women, menstrual effects on regional pain outcomes have not been investigated in this clinical population. This study evaluated menstrual effects on mechanical pain sensitivity (pressure pain threshold [PPT]), neck pain intensity (numeric pain rating scale [NPRS]), and neck-related disability (Neck Disability Index [NDI]) in 22 normally menstruating (NM) and 17 hormonal contraceptive users with chronic neck pain. Sex hormones, PPT, and NDI were measured during the early follicular (F1), late follicular (F2), and luteal (L) menstrual phases. Daily NPRS scores were recorded in an online symptom diary and averaged within each phase. Estradiol and progesterone increased only for NM women in F2 and L, respectively. Phase effects on PPT (η(2) = .003), NDI (η(2) = .003), and NPRS (η(2) = .016) for NM women were small and did not differ from those for the hormonal contraceptive users (P ≥ .386). Averaged across the menstrual cycle, PPT scores explained 29% of the variance in NPRS scores for NM women but were not associated with NDI scores in either group. Results indicate that the magnitude of menstrual effects on mechanical pain sensitivity and the severity of neck pain and disability do not exceed thresholds of clinically detectable change in women with chronic neck pain.

PERSPECTIVE

Fluctuations in evoked and clinical pain outcomes across the menstrual cycle do not appear to be of sufficient magnitude to impact clinical decision making for women with chronic neck pain.

Emotional modulation of pain and spinal nociception in persons with major depressive disorder (MDD)

Major depressive disorder (MDD) is associated with risk for chronic pain, but the mechanisms contributing to the MDD and pain relationship are unclear. To examine whether disrupted emotional modulation of pain might contribute, this study assessed emotional processing and emotional modulation of pain in healthy controls and unmedicated persons with MDD (14 MDD, 14 controls). Emotionally charged pictures (erotica, neutral, mutilation) were presented in 4 blocks. Two blocks assessed physiological-emotional reactions (pleasure/arousal ratings, corrugator electromyography (EMG), startle modulation, skin conductance) in the absence of pain and 2 blocks assessed emotional modulation of pain and the nociceptive flexion reflex (NFR, a physiological measure of spinal nociception) evoked by suprathreshold electric stimulations. Results indicated pictures generally evoked the intended emotional responses; erotic pictures elicited pleasure, subjective arousal, and smaller startle magnitudes, whereas mutilation pictures elicited displeasure, corrugator EMG activation, and subjective/physiological arousal. However, emotional processing was partially disrupted in MDD, as evidenced by a blunted pleasure response to erotica and a failure to modulate startle according to a valence linear trend. Furthermore, emotional modulation of pain was observed in controls but not MDD, even though there were no group differences in NFR threshold or emotional modulation of NFR. Together, these results suggest supraspinal processes associated with emotion processing and emotional modulation of pain may be disrupted in MDD, but brain to spinal cord processes that modulate spinal nociception are intact. Thus, emotional modulation of pain deficits may be a phenotypic marker for future pain risk in MDD.

Sex differences in pain: a brief review of clinical and experimental findings

Recent years have witnessed substantially increased research regarding sex differences in pain. The expansive body of literature in this area clearly suggests that men and women differ in their responses to pain, with increased pain sensitivity and risk for clinical pain commonly being observed among women. Also, differences in responsivity to pharmacological and non-pharmacological pain interventions have been observed; however, these effects are not always consistent and appear dependent on treatment type and characteristics of both the pain and the provider. Although the specific aetiological basis underlying these sex differences is unknown, it seems inevitable that multiple biological and psychosocial processes are contributing factors. For instance, emerging evidence suggests that genotype and endogenous opioid functioning play a causal role in these disparities, and considerable literature implicates sex hormones as factors influencing pain sensitivity. However, the specific modulatory effect of sex hormones on pain among men and women requires further exploration. Psychosocial processes such as pain coping and early-life exposure to stress may also explain sex differences in pain, in addition to stereotypical gender roles that may contribute to differences in pain expression. Therefore, this review will provide a brief overview of the extant literature examining sex-related differences in clinical and experimental pain, and highlights several biopsychosocial mechanisms implicated in these male-female differences. The future directions of this field of research are discussed with an emphasis aimed towards further elucidation of mechanisms which may inform future efforts to develop sex-specific treatments.