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Brief Report  |   March 2019
Thermal and Mechanical Pain Thresholds of Women With Provoked Localized Vulvodynia: A Pilot Study
Author Notes
  • From the Departments of Biomedical Sciences (Dr Basha) and Clinical Sciences (Dr Nazar) at the West Virginia School of Osteopathic Medicine in Lewisburg; the Department of Obstetrics and Gynecology at Drexel University College of Medicine in Philadelphia, Pennsylvania (Drs Kellogg-Spadt, Ruberu, and Whitmore); the Department of Obstetrics and Gynecology at Summa Health System in Akron, Ohio (Dr Burrows); and the Department of Human Science, School of Nursing and Health Studies at Georgetown University in Washington, DC (Ms Wallach). 
  • Financial Disclosures: None reported. 
  • Support: This study was supported by a Professional Enrichment and Growth Award (Drexel University College of Medicine) and a National Vulvodynia Association Grant awarded to Dr Basha. 
  •  *Address correspondence to Maureen E. Basha, PhD, Department of Physiology, Louisiana State University Health Sciences Center, 1901 Perdido St, New Orleans, LA 70112-1393. Email: mbash1@lsuhsc.edu
     
Article Information
Neuromusculoskeletal Disorders / Obstetrics and Gynecology / Pain Management/Palliative Care
Brief Report   |   March 2019
Thermal and Mechanical Pain Thresholds of Women With Provoked Localized Vulvodynia: A Pilot Study
The Journal of the American Osteopathic Association, March 2019, Vol. 119, 164-172. doi:https://doi.org/10.7556/jaoa.2019.027
The Journal of the American Osteopathic Association, March 2019, Vol. 119, 164-172. doi:https://doi.org/10.7556/jaoa.2019.027
Abstract

Context: Vulvodynia is a chronic pain condition defined as vulvar pain lasting at least 3 months in the absence of gross anatomic or neurologic findings. Provoked, localized vulvodynia (PLV), a subtype of vulvodynia, is characterized by vestibular pain in response to light touch. The cause of PLV remains largely unknown, and triggering events have yet to be determined.

Objective: To evaluate vestibular and peripheral experimental pain thresholds in patients with PLV to further define the somatosensory profile of these patients.

Methods: After informed consent was provided, eligible participants completed a questionnaire and underwent quantitative sensory testing at the forearm and posterior vestibule. Detection and pain thresholds to thermal (cold and heat) and mechanical (pressure) stimuli were measured.

Results: Seventeen participants with PLV and 16 control participants were included. Participants in the PLV group scored lower on the patient health questionnaire 9 (PHQ-9) compared with those in the control group (P<.05) and had higher ratings of self-reported genital pain with sex (P<.001) and daily activity (P<.05). Forearm pain thresholds to cold (P<.01) and heat (P<.01) stimuli were also lower in the PLV group compared with those in the control group. Vestibular pain thresholds to cold (P<.05) and pressure (P<.01) stimuli were also lower in the PLV group.

Conclusion: Lower scores on the PHQ-9 and higher self-reported genital pain ratings of patients with PLV highlight the significant impact of this poorly understood condition on quality of life. Quantitative sensory testing results demonstrated that vestibular cold allodynia may be a somatosensory feature of PLV. Reduced forearm pain thresholds in these patients suggest altered sensory processing at extrapelvic sites, although it is unclear whether these measurements are related to central sensitization.

The International Society for the Study of Vulvovaginal Disease defines vulvodynia as vulvar discomfort/pain in the absence of anatomic or neurologic findings to explain the pain and is, in essence, a diagnosis of exclusion. Its triggering event remains unknown. Estimates of prevalence of vulvodynia range from 3.8% to 8.3% of the US female population,1-3 and it has been reported as the leading cause of dyspareunia in premenopausal women.2 Vulvodynia is subcategorized according to the location of the pain (generalized, localized, mixed) and whether the pain is spontaneous, experienced on provocation, or both (mixed). To date, the majority of vulvodynia research has focused on provoked localized vulvodynia (PLV). The vulvar vestibule is the most common site of PLV, and idiopathic vestibular pain is referred to as provoked vestibulodynia. Provoked localized vulvodynia is further classified by the timing of the onset of vulvar pain. Primary PLV, also referred to as early-onset PLV, is defined by the onset of vulvar pain at the first episode of vaginal penetration (ie, provoked vulvar pain since the first attempt at intercourse or tampon insertion). Secondary PLV, also referred to as late-onset PLV, is defined by vulvar pain with vaginal penetration following a period when vaginal penetration was pain-free. 
Studies have suggested that PLV is associated with (1) chronic inflammation; (2) previous exposure to vulvovaginal infections that leads to hypersensitivity of the vestibule; (3) altered central processing of vestibular stimuli; (4) hyperinnervation of the vestibule; (5) combined oral contraceptive use; and (6) gene polymorphisms indicative of genetic risk. There is also evidence that PLV is associated with levator ani spasm, also known as pelvic floor hypertonus.4 The disorder is likely linked to all of these factors, and treatment requires customized approaches for each patient and often the expertise of a multidisciplinary team. Osteopathic approaches have received limited attention as a component of PLV management despite its potential contribution to the treatment of patients with vulvar pain and pelvic floor hypertonus. 
Vestibular pain in response to light touch (mechanical allodynia) is a hallmark symptom of PLV and is qualitatively assessed by palpating the vulva with a cotton-tipped swab during clinical examination. Quantitative sensory testing has been used in clinical studies to define the somatosensory profile of PLV. Decreased vestibular detection thresholds to tactile5,6 but not heat stimuli7 have been reported in patients with PLV. Additionally, reduced vestibular experimental pain thresholds to punctate,5,8 pressure,6,7,9,10 and heat7-9 stimuli have been documented in patients with PLV. Increased pain sensitivity to mechanical and heat stimuli at peripheral sites (eg, forearm, thumb) in women with PLV has been reported in some5,10-13 but not all14 studies. Vestibular or peripheral cold pain thresholds have not been investigated in most of these studies.5-7,9-14 
Advancing our understanding of the phenotype of pain in patients with PLV is an important step in stratifying patients based on the underlying pathogenesis of pain and refining treatment strategies for this poorly understood condition. To date, research related to the sensory processing of cold pain in patients with PLV is limited to a 2001 qualitative report by Bohm-Starke et al.8 The objective of the current study, therefore, was to investigate the somatosensory profile of patients with PLV through comparing thermal (cold and heat) and mechanical (pressure) pain thresholds in patients with PLV. 
Methods
The protocol for this study was approved by the institutional review boards of Drexel University College of Medicine and Georgetown University. This study was not registered as a clinical trial because it did not meet the federal definition of a clinical trial. Women were recruited for participation in the study using flyers posted on college campuses and the National Vulvodynia Association website. Additionally, women with clinically diagnosed PLV by a vulvar specialist at the Pelvic and Sexual Health Institute in Philadelphia, Pennsylvania, and the Center for Vulvovaginal Diseases in Washington, DC, were approached to consider enrollment in the study. Inclusion criteria for study groups were age of 18 to 55 years and a clinically confirmed diagnosis of PLV (PLV group) or without a diagnosis of PLV and self-reported lack of vulvar pain or other chronic pain conditions (control group). Exclusion criteria were current vulvovaginal infections, current pregnancy, postmenopausal status, history of vaginal surgery for prolapse repair or vulvar surgery, vaginismus, or major medical or psychiatric illness. Women with PLV with comorbid widespread pain conditions (fibromyalgia and chronic regional pain syndrome) were excluded. 
After written informed consent, participants completed a semistandardized questionnaire (patient health questionnaire 9 [PHQ-9]) that included demographic questions, clinical characteristics, and visual analogue scales on a 100-mm ruler for genital pain with sexual intercourse and with daily activity. Participants underwent quantitative sensory testing (QST) after completion of the PHQ-9. For participants with regular menstrual cycles, QST was scheduled between days 7 and 12 of the follicular phase of the cycle. For participants taking oral contraceptives, QST was scheduled between day 7 and 12 after the first placebo pill. We selected a sample size similar to the previous study8 of vulvar cold pain thresholds for comparative purposes. All participants received $50.00 for their participation. 
Detection and pain thresholds to thermal stimuli (cold and heat) were assessed using a thermosensory analyzer equipped with a 5 × 5-mm2 contact thermode. A temperature range of 0°C to 50°C was used for measurements of thermal detection and pain thresholds. The method of limits was used, in which the intensity of the applied thermal stimulus increased or decreased until the participant stopped the stimulus with a handheld mouse when the stimulus was first perceived (detection) or when the stimulus was perceived as painful (experimental pain threshold). The QST was performed at the left volar forearm as a measurement of somatosensory processing at a site peripheral to the vulva. The QST was then performed in the posterior vestibule (left and right sides). We selected the posterior vestibule as the measurement site, as it was demonstrated that the posterior vestibule was the most sensitive site in patients with PLV,8 in agreement with clinical reports of the posterior vestibule being the most common site of pain.15 Pain thresholds to mechanical stimuli were assessed using a commercially available algometer equipped with either a blunt tip for forearm measurements or with a cotton-tipped applicator for vestibular measurements. A pressure range of 0 to 4 kg and 0 to 500 g was used for measurements of forearm and vestibular pressure pain thresholds, respectively. 
The cutoff values (0°C for cold pain, 50°C for heat pain, and 500 g and 4 kg for vestibular and forearm pressure pain, respectively) were assigned as the pain threshold for participants who did not report pain within the range of applied stimulus. The starting temperature for thermal measurements was 32°C, with a rate of change of 1°C per second. Thermal stimuli were applied in the following fixed order: cold detection (3 repetitions), warmth detection (3 repetitions), cold pain (2 repetitions), and heat pain (2 repetitions). Participants were asked to rate their pain intensity on a scale of 0 (no pain at all) to 10 (worst pain imaginable) using a verbal numerical rating scale after each pain measurement. 
Statistical Analysis
Data are presented as the means and SEs of the means for continuous variables and the frequencies and percentages of categorical variables. For continuous variables, differences between the averages were tested using t tests when normality assumptions were satisfied. Differences between the left and right vestibule were compared using paired t tests, and differences between the PLV group and the control group were compared using unpaired t tests. The nonparametric Wilcoxon rank sum test (unpaired comparisons) and Wilcoxon matched pair test (paired comparisons) were used to examine differences if normality assumptions were not satisfied. For categorical variables, χ2 and Fisher exact tests were used to examine differences between 2 groups. 
Results
Seventeen participants were included in the PLV group and 16 in the control group (N=33; Table 1). Age, age at menarche, body mass index, parity, hormonal contraceptive use, handedness, marital status, education, and smoking status were not significantly different between the PLV group and the control group. The majority of participants were white (16 of 17 [94%] in the PLV group and 12 of 16 [75%] in the control group). The PHQ-9 score was lower in the PLV group (P<.05), with 1 participant scoring greater than or equal to 15, which suggested the presence of major depression. Self-reports (visual analogue scale) of genital pain with sexual activity (P<.001) and daily activity (P<.05) were significantly higher in the PLV group compared with the control group. Five participants in the PLV group reported the presence of an additional chronic pain condition (Table 1). 
Table 1.
Thermal and Mechanical Pain Thresholds of Women With PLV: Demographic and Clinical Characteristics of Participants
Characteristic PLV (n=17) Control (n=16) P Value
Age, Mean (SE) 34.3 (2.4) 31.1 (1.9) .312
Age at Menarche, Mean (SE) 12.1 (0.4) 12.4 (0.4) .656
BMI, Mean (SE) 26.9 (2.0) 25.2 (4.6) .985
Nulliparous, No. (%) 11 (65) 12 (75) .708
Race, No. (%) .453
 White 16 (94) 12 (75)
 Black 1 (6) 2 (13)
 White Hispanic 0 1 (6)
 Asian 0 1 (6)
Hormonal Contraceptive Use, No. (%) 6 (35) 6 (38) .800
Left-Handedness, No. (%) 1 (6) 3 (19) .335
Marital Status, No. (%) .173
 Single 9 (53) 12 (75)
 Married 7 (41) 2 (13)
 Divorced 1(6) 2 (13)
Education, No. (%) .209
 High school graduate 2 (21) 2 (13)
 College graduate 8 (42) 3 (19)
 Post graduate/doctoral degree 7 (37) 11 (69)
Income, No. (%) .412
 <$20,000 2 (12) 5 (31)
 $20-49,999 4 (24) 5 (31)
 $50-99,999 5 (30) 3 (19)
 ≥$100,000 6 (4) 3 (19)
Smoker, No. (%) 0 3 (19) .103
Patient Health Questionnaire 9 Score, Mean (SE) 4.3 (1.3) 1.7 (0.6) <.05
Patient Health Questionnaire Score ≥15, No. (%) 1 (6) 0 .325
VAS Genital Pain With Sexual Activity, Mean (SE) 6.4 (0.8) 0.3 (0.2) <.001

Abbreviations: BMI, body mass index; IBS, irritable bowel syndrome; PBS/IC, painful bladder syndrome/interstitial cystitis; PLV, provoked localized vulvodynia; VAS, visual analogue scale.

Table 1.
Thermal and Mechanical Pain Thresholds of Women With PLV: Demographic and Clinical Characteristics of Participants
Characteristic PLV (n=17) Control (n=16) P Value
Age, Mean (SE) 34.3 (2.4) 31.1 (1.9) .312
Age at Menarche, Mean (SE) 12.1 (0.4) 12.4 (0.4) .656
BMI, Mean (SE) 26.9 (2.0) 25.2 (4.6) .985
Nulliparous, No. (%) 11 (65) 12 (75) .708
Race, No. (%) .453
 White 16 (94) 12 (75)
 Black 1 (6) 2 (13)
 White Hispanic 0 1 (6)
 Asian 0 1 (6)
Hormonal Contraceptive Use, No. (%) 6 (35) 6 (38) .800
Left-Handedness, No. (%) 1 (6) 3 (19) .335
Marital Status, No. (%) .173
 Single 9 (53) 12 (75)
 Married 7 (41) 2 (13)
 Divorced 1(6) 2 (13)
Education, No. (%) .209
 High school graduate 2 (21) 2 (13)
 College graduate 8 (42) 3 (19)
 Post graduate/doctoral degree 7 (37) 11 (69)
Income, No. (%) .412
 <$20,000 2 (12) 5 (31)
 $20-49,999 4 (24) 5 (31)
 $50-99,999 5 (30) 3 (19)
 ≥$100,000 6 (4) 3 (19)
Smoker, No. (%) 0 3 (19) .103
Patient Health Questionnaire 9 Score, Mean (SE) 4.3 (1.3) 1.7 (0.6) <.05
Patient Health Questionnaire Score ≥15, No. (%) 1 (6) 0 .325
VAS Genital Pain With Sexual Activity, Mean (SE) 6.4 (0.8) 0.3 (0.2) <.001

Abbreviations: BMI, body mass index; IBS, irritable bowel syndrome; PBS/IC, painful bladder syndrome/interstitial cystitis; PLV, provoked localized vulvodynia; VAS, visual analogue scale.

×
Quantitative Sensory Testing
Detection Thresholds
No differences in thermal detection thresholds were recorded between the right and left vestibule in the PLV and control group. Vestibular and forearm thermal detection thresholds were also similar between the PLV and control groups (data not shown). 
Pain Thresholds
Forearm
Although the forearm pressure pain threshold tended to be lower in the PLV group, this difference was not significant (Figure 1A). Left forearm cold (P<.01) and heat (P<.01) pain thresholds were significantly lower in the PLV group compared with the control group (Figure 1B and 1C). No significant differences were found between the PLV and control groups’ pain ratings (verbal numerical rating scale) regarding the forearm pain thresholds to any stimuli applied (Table 2). 
Figure 1.
Left forearm pain thresholds of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds at the left forearm where not significantly different between the PLV and control group. (B) Pain thresholds to heat stimuli were significantly lower in the PLV group compared with the control group (P<.01). (C) Pain thresholds to cold stimuli were also significantly lower in the PLV group compared with the control group (P<.01).
Figure 1.
Left forearm pain thresholds of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds at the left forearm where not significantly different between the PLV and control group. (B) Pain thresholds to heat stimuli were significantly lower in the PLV group compared with the control group (P<.01). (C) Pain thresholds to cold stimuli were also significantly lower in the PLV group compared with the control group (P<.01).
Table 2.
Left Forearm and Vestibular Pain Ratings in the PLV and Control Groups (N=33)
Pain Rating, Mean (SD)a
Sensory Testing PLV Control P Value
Pressure
 Forearm Left 3.0 (0.6) 2.1 (0.5) .262
 PV Right 4.2 (0.4) 3.8 (0.6) .575
 PV Left 4.7 (0.6) 3.6 (0.6) .170
Cold
 Forearm Left 2.6 (0.4 2.2 (0.7) .608
 PV Right 4.0 (0.6) 3.8 (0.6) .338
 PV Left 3.9 (0.5) 3.4 (0.5) .488
Heat
 Forearm Left 4.3 (0.5) 4.4 (0.6) .915
 PV Right 4.4 (0.6) 3.8 (0.6) .339
 PV Left 4.4 (0.5) 4.1 (0.6) .686

a Pain was rated on a scale of 0 (no pain) to 10 (worst imaginable pain).

Abbreviations: PLV, provoked localized vulvodynia; PV, posterior vestibule.

Table 2.
Left Forearm and Vestibular Pain Ratings in the PLV and Control Groups (N=33)
Pain Rating, Mean (SD)a
Sensory Testing PLV Control P Value
Pressure
 Forearm Left 3.0 (0.6) 2.1 (0.5) .262
 PV Right 4.2 (0.4) 3.8 (0.6) .575
 PV Left 4.7 (0.6) 3.6 (0.6) .170
Cold
 Forearm Left 2.6 (0.4 2.2 (0.7) .608
 PV Right 4.0 (0.6) 3.8 (0.6) .338
 PV Left 3.9 (0.5) 3.4 (0.5) .488
Heat
 Forearm Left 4.3 (0.5) 4.4 (0.6) .915
 PV Right 4.4 (0.6) 3.8 (0.6) .339
 PV Left 4.4 (0.5) 4.1 (0.6) .686

a Pain was rated on a scale of 0 (no pain) to 10 (worst imaginable pain).

Abbreviations: PLV, provoked localized vulvodynia; PV, posterior vestibule.

×
Vestibule
Thermal and mechanical pain thresholds and ratings of pain (verbal numerical rating scale) were similar between the right and left vestibule in the PLV and control groups. Pain thresholds to cold were significantly lower at the right (P<.01) and left (P<.05) posterior vestibule in the PLV group compared with the respective side in the control group (Figure 2C). Heat pain thresholds in the PLV group were significantly lower on the right (P<.05) compared with the respective side of the control group (Figure 2B). Pressure pain thresholds were approximately 2-fold lower on the right (P<.01) and left (P<.001) posterior vestibule of the PLV compared with the control group (Figure 2A). Ratings of evoked pain were similar between groups (Table 2). 
Figure 2.
Vestibular pain thresholds measured at the right and left posterior vestibule of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds were significantly lower at both the right (P<.01) and left (P<.001) posterior vestibule of PLV group compared with the respective vestibular side of control group. (B) Right vestibular heat pain threshold was significantly (P<.05) lower in the PLV group compared with the respective side of the control group. (C) Cold pain thresholds were significantly lower in the left (P<.01) and right (P<.05) vestibule in the PLV group compared with the respective vestibular side of the control group. No differences in pain thresholds to any of the stimuli tested were detected between the right and left vestibule in either group.
Figure 2.
Vestibular pain thresholds measured at the right and left posterior vestibule of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds were significantly lower at both the right (P<.01) and left (P<.001) posterior vestibule of PLV group compared with the respective vestibular side of control group. (B) Right vestibular heat pain threshold was significantly (P<.05) lower in the PLV group compared with the respective side of the control group. (C) Cold pain thresholds were significantly lower in the left (P<.01) and right (P<.05) vestibule in the PLV group compared with the respective vestibular side of the control group. No differences in pain thresholds to any of the stimuli tested were detected between the right and left vestibule in either group.
Discussion
The major finding of this study was 2-fold lower vestibular cold pain thresholds (cold pain reported at higher temperatures) in participants with PLV compared with control participants. To date, little attention has been paid to cold pain thresholds in this patient population despite numerous reports of decreased cold pain thresholds in QST studies of other types of chronic pain.16-21 A 2001 study reported qualitative differences in vestibular cold pain thresholds in patients with PLV compared with controls.8 Subsequent QST studies of patients with PLV did not include vestibular pain thresholds to cold stimuli in the QST protocol.5-7,9,10 In the study by Bohm-Starke et al,8 the majority of participants did not report cold pain in the posterior vestibule within the range of testing temperatures (31°C-6°C), which limited the ability to identify differences in cold pain thresholds. We therefore used a testing range of 32°C to 0°C, and 2 control participants did not report pain at 0°C. Our finding in the current study corroborates the qualitative report of Bohm-Starke et al.8 Together, these 2 studies suggest that cold allodynia is a component of the somatosensory profile of some patients with PLV and may provide insight into distinct underlying pathologic mechanisms in this subset of patients. Studies18,22,23 of other chronic pain conditions that used a QST protocol subgrouped patients according to cold pain thresholds to initiate a mechanistically based classification scheme emphasizing the importance of the current findings; however, much work remains to be done to reach the goal of treatment targeted to the pathophysiologic mechanisms underlying an individual patient's pain. Large-scale, comprehensive QST studies are needed to identify subgroups of patients with vulvodynia based on somatosensory profiles and potentially different mechanisms of pain pathogenesis—a necessary step for the refinement of standard of care algorithms for vulvodynia. 
Self-reported ratings of genital pain with sexual and daily activity were higher in patients with PLV compared with controls (Table 1), highlighting the effects of PLV on overall quality of life. Although pain ratings of pressure pain thresholds were not different between groups, the threshold at which pain was reported was lower in patients with PLV (Figure 2A) than in controls. In contrast to studies using homemade vulvar algesiometers,6,7,10,12,24 we used a commercially available algometer with a customized attachment for a cotton-tipped applicator and replicated previous findings of lower pressure pain thresholds in patients with PLV. This novel device may be useful for multicenter site studies, which require standard operating procedures across institutions, although future studies of inter- and intrarater reliability are needed. These algometers may also be useful as a tool to assess response to treatment in a clinical setting. 
We reported lower vestibular heat pain thresholds in the right vestibule of patients with PLV compared with controls (Figure 2B). Other studies6-8 have also reported lower vestibular heat pain thresholds in patients with PLV. 
Our report of normal vestibular thermal sensory detection thresholds combined with reduced thermal (cold and heat) and mechanical pain thresholds provides further evidence that central sensitization contributes to the chronic vulvar pain of some patients with PLV. Although we did not evaluate pelvic floor function in this study, it is important to note that pelvic floor hypertonicity may also contribute to PLV pain. Therefore, it is recommended that the muscles of the pelvic floor, with attention to the levator ani and coccygeal muscle, be evaluated in these patients and that OMT techniques, including muscle energy and myofascial release, be considered in patients with evidence of hypertonicity. Furthermore, it should be acknowledged that the relative roles of thermoreceptor (eg, transient receptor potential cation channel subfamily M member 8), peripheral nervous system, or central nervous system dysfunction in patients with chronic pain remain incompletely defined.25 It is possible that restoration of autonomic tone may be beneficial in pelvic pain conditions such as vulvodynia, and somatic dysfunctions of the pubic bone and sacrum should be evaluated and managed. Specifically, sacral dysfunction may alter both parasympathetic tone through pelvic splanchnic intervention at S2-4, as well as sympathetic tone at these levels, which could affect external genitalia. 
Reduced mechanical5,10,12,13 and heat26 pain thresholds have been reported at peripheral body regions in patients with PLV. In the current study, we found lower thermal (cold and heat) but not mechanical pain thresholds at the forearm (Figure 1). In light of the evidence of increased peripheral pain sensitivity, tender point examination should be considered as part of the clinical assessment of patients with PLV. Decreased pain thresholds at peripheral sites and reports of high rates of coexistence of PLV with other chronic pain disorders have also been suggested as evidence of central sensitization of pain in patients with PLV. However, because it is not always clear whether comorbid chronic pain conditions are used as exclusion criteria in PLV studies,10,12,13,26 QST studies that report altered peripheral pain thresholds in patients with PLV should be interpreted with caution. We excluded patients with widespread pain conditions that would directly affect peripheral measurements but not patients with comorbid visceral pain conditions. A 2009 study7 failed to detect differences in forearm heat and mechanical pain thresholds in patients with PLV when the presence of other chronic pain conditions were used as exclusion criteria. It is possible, however, that this lack of difference is due to conservative cutoff pressures for applied pressure, which underestimates pain thresholds.7 More research is required to determine the contribution of central sensitization to the pathogenesis of pain in patients with vulvodynia. Furthermore, studies are needed to determine whether somatic dysfunction contributes to the pain profile of patients with PLV and to evaluate the effectiveness of OMT techniques, such as strain-counterstrain, as treatment options for women with this chronic pain disorder. 
It has been documented that PLV is associated with depression, stress, anxiety, and relationship distress.4 Similarly, we report that the PLV group had more depressive symptoms (Table 1). A community-based study showed that antecedent depression increased the risk of PLV, and PLV also increased the risk of new psychological conditions developing.27 The impact of PLV on a woman's physical, psychological, social, and relational well-being highlights the importance of incorporating the mind-body-spirit philosophy of osteopathic medicine into the care for these patients. 
Limitations
As a pilot study, our group sizes were small, and we did not differentiate between primary and secondary PLV. There is evidence of psychophysical and psychosexual differences between patients with primary and secondary PLV,14,28,29 suggesting that these groups have distinct mechanisms of pain. Additionally, we only performed 2 repetitions of pain thresholds to minimize patient burden of these procedures despite the improvement in reliability with increased repetitions. Because of our recruitment method, QST measurements were not blinded. However, as participants were in control of determining their pain thresholds, this method likely did not have a significant impact on recorded values. 
Conclusion
Although vestibular sensory detection thresholds were similar in PLV and control groups, mechanical and cold pain thresholds were lower. Additionally, peripheral pain thresholds were lower in the PLV group. Taken together, our results provide further evidence of central sensitization of pain in patients with PLV and emphasize the importance of treating the whole person, as PLV involves more than just localized pain. Studies that examine the effect of OMT approaches on vulvar pain, pelvic floor dysfunction, and systemic pain in patients with PLV would help further define the role of OMT in the management of PLV. 
Acknowledgment
We thank Eshetu Tefera, MS, in the Department of Biostatistics and Epidemiology at Medstar Health Research Institute in Washington, DC, for his assistance with statistical analysis. 
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Figure 1.
Left forearm pain thresholds of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds at the left forearm where not significantly different between the PLV and control group. (B) Pain thresholds to heat stimuli were significantly lower in the PLV group compared with the control group (P<.01). (C) Pain thresholds to cold stimuli were also significantly lower in the PLV group compared with the control group (P<.01).
Figure 1.
Left forearm pain thresholds of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds at the left forearm where not significantly different between the PLV and control group. (B) Pain thresholds to heat stimuli were significantly lower in the PLV group compared with the control group (P<.01). (C) Pain thresholds to cold stimuli were also significantly lower in the PLV group compared with the control group (P<.01).
Figure 2.
Vestibular pain thresholds measured at the right and left posterior vestibule of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds were significantly lower at both the right (P<.01) and left (P<.001) posterior vestibule of PLV group compared with the respective vestibular side of control group. (B) Right vestibular heat pain threshold was significantly (P<.05) lower in the PLV group compared with the respective side of the control group. (C) Cold pain thresholds were significantly lower in the left (P<.01) and right (P<.05) vestibule in the PLV group compared with the respective vestibular side of the control group. No differences in pain thresholds to any of the stimuli tested were detected between the right and left vestibule in either group.
Figure 2.
Vestibular pain thresholds measured at the right and left posterior vestibule of participants with provoked localized vulvodynia (PLV) (n=17) and control participants (n=16). (A) Pressure pain thresholds were significantly lower at both the right (P<.01) and left (P<.001) posterior vestibule of PLV group compared with the respective vestibular side of control group. (B) Right vestibular heat pain threshold was significantly (P<.05) lower in the PLV group compared with the respective side of the control group. (C) Cold pain thresholds were significantly lower in the left (P<.01) and right (P<.05) vestibule in the PLV group compared with the respective vestibular side of the control group. No differences in pain thresholds to any of the stimuli tested were detected between the right and left vestibule in either group.
Table 1.
Thermal and Mechanical Pain Thresholds of Women With PLV: Demographic and Clinical Characteristics of Participants
Characteristic PLV (n=17) Control (n=16) P Value
Age, Mean (SE) 34.3 (2.4) 31.1 (1.9) .312
Age at Menarche, Mean (SE) 12.1 (0.4) 12.4 (0.4) .656
BMI, Mean (SE) 26.9 (2.0) 25.2 (4.6) .985
Nulliparous, No. (%) 11 (65) 12 (75) .708
Race, No. (%) .453
 White 16 (94) 12 (75)
 Black 1 (6) 2 (13)
 White Hispanic 0 1 (6)
 Asian 0 1 (6)
Hormonal Contraceptive Use, No. (%) 6 (35) 6 (38) .800
Left-Handedness, No. (%) 1 (6) 3 (19) .335
Marital Status, No. (%) .173
 Single 9 (53) 12 (75)
 Married 7 (41) 2 (13)
 Divorced 1(6) 2 (13)
Education, No. (%) .209
 High school graduate 2 (21) 2 (13)
 College graduate 8 (42) 3 (19)
 Post graduate/doctoral degree 7 (37) 11 (69)
Income, No. (%) .412
 <$20,000 2 (12) 5 (31)
 $20-49,999 4 (24) 5 (31)
 $50-99,999 5 (30) 3 (19)
 ≥$100,000 6 (4) 3 (19)
Smoker, No. (%) 0 3 (19) .103
Patient Health Questionnaire 9 Score, Mean (SE) 4.3 (1.3) 1.7 (0.6) <.05
Patient Health Questionnaire Score ≥15, No. (%) 1 (6) 0 .325
VAS Genital Pain With Sexual Activity, Mean (SE) 6.4 (0.8) 0.3 (0.2) <.001

Abbreviations: BMI, body mass index; IBS, irritable bowel syndrome; PBS/IC, painful bladder syndrome/interstitial cystitis; PLV, provoked localized vulvodynia; VAS, visual analogue scale.

Table 1.
Thermal and Mechanical Pain Thresholds of Women With PLV: Demographic and Clinical Characteristics of Participants
Characteristic PLV (n=17) Control (n=16) P Value
Age, Mean (SE) 34.3 (2.4) 31.1 (1.9) .312
Age at Menarche, Mean (SE) 12.1 (0.4) 12.4 (0.4) .656
BMI, Mean (SE) 26.9 (2.0) 25.2 (4.6) .985
Nulliparous, No. (%) 11 (65) 12 (75) .708
Race, No. (%) .453
 White 16 (94) 12 (75)
 Black 1 (6) 2 (13)
 White Hispanic 0 1 (6)
 Asian 0 1 (6)
Hormonal Contraceptive Use, No. (%) 6 (35) 6 (38) .800
Left-Handedness, No. (%) 1 (6) 3 (19) .335
Marital Status, No. (%) .173
 Single 9 (53) 12 (75)
 Married 7 (41) 2 (13)
 Divorced 1(6) 2 (13)
Education, No. (%) .209
 High school graduate 2 (21) 2 (13)
 College graduate 8 (42) 3 (19)
 Post graduate/doctoral degree 7 (37) 11 (69)
Income, No. (%) .412
 <$20,000 2 (12) 5 (31)
 $20-49,999 4 (24) 5 (31)
 $50-99,999 5 (30) 3 (19)
 ≥$100,000 6 (4) 3 (19)
Smoker, No. (%) 0 3 (19) .103
Patient Health Questionnaire 9 Score, Mean (SE) 4.3 (1.3) 1.7 (0.6) <.05
Patient Health Questionnaire Score ≥15, No. (%) 1 (6) 0 .325
VAS Genital Pain With Sexual Activity, Mean (SE) 6.4 (0.8) 0.3 (0.2) <.001

Abbreviations: BMI, body mass index; IBS, irritable bowel syndrome; PBS/IC, painful bladder syndrome/interstitial cystitis; PLV, provoked localized vulvodynia; VAS, visual analogue scale.

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Table 2.
Left Forearm and Vestibular Pain Ratings in the PLV and Control Groups (N=33)
Pain Rating, Mean (SD)a
Sensory Testing PLV Control P Value
Pressure
 Forearm Left 3.0 (0.6) 2.1 (0.5) .262
 PV Right 4.2 (0.4) 3.8 (0.6) .575
 PV Left 4.7 (0.6) 3.6 (0.6) .170
Cold
 Forearm Left 2.6 (0.4 2.2 (0.7) .608
 PV Right 4.0 (0.6) 3.8 (0.6) .338
 PV Left 3.9 (0.5) 3.4 (0.5) .488
Heat
 Forearm Left 4.3 (0.5) 4.4 (0.6) .915
 PV Right 4.4 (0.6) 3.8 (0.6) .339
 PV Left 4.4 (0.5) 4.1 (0.6) .686

a Pain was rated on a scale of 0 (no pain) to 10 (worst imaginable pain).

Abbreviations: PLV, provoked localized vulvodynia; PV, posterior vestibule.

Table 2.
Left Forearm and Vestibular Pain Ratings in the PLV and Control Groups (N=33)
Pain Rating, Mean (SD)a
Sensory Testing PLV Control P Value
Pressure
 Forearm Left 3.0 (0.6) 2.1 (0.5) .262
 PV Right 4.2 (0.4) 3.8 (0.6) .575
 PV Left 4.7 (0.6) 3.6 (0.6) .170
Cold
 Forearm Left 2.6 (0.4 2.2 (0.7) .608
 PV Right 4.0 (0.6) 3.8 (0.6) .338
 PV Left 3.9 (0.5) 3.4 (0.5) .488
Heat
 Forearm Left 4.3 (0.5) 4.4 (0.6) .915
 PV Right 4.4 (0.6) 3.8 (0.6) .339
 PV Left 4.4 (0.5) 4.1 (0.6) .686

a Pain was rated on a scale of 0 (no pain) to 10 (worst imaginable pain).

Abbreviations: PLV, provoked localized vulvodynia; PV, posterior vestibule.

×