Vulvodynia is a disorder characterized by ongoing neuropathic pain at the vulva/introitus that is not due to treatable infectious or dermatologic conditions. Many women treated for vulvodynia report pain duration of many years. The cause is unknown, although genetic, immunologic, and environmental factors have been suggested.1–4
Until recently, vulvodynia was thought to be rare. Additional studies, however, indicate this is not the case. Its prevalence has been reported to be between 3.1% and 15%,5–8 with the non–clinic-based studies converging on a prevalence of approximately 7% when validated by examination.8 Moreover, vulvodynia was thought to be chronic until reports indicated that substantial proportions of women reported remission of symptoms.6,7 Prospective studies are needed to estimate the incidence rates of vulvodynia, the probability of remission, and their associated factors.
In 2006, we surveyed women who had been enrolled in our previous validation study of the prevalence of vulvodynia among members of the University of Michigan Women’s Health Registry.8 The objective of this study was to estimate the incidence and remission rates and to identify factors potentially associated with these outcomes.
MATERIALS AND METHODS
Institutional review board approval for this study was obtained from the University of Michigan Human Subjects Committee. A letter of introduction and a survey were sent between September 2006 and March 2007 to all participants from our previous survey of women in the University of Michigan Women’s Health Registry.8 In brief, that 2004 study on 1,037 of 1,446 eligible women who completed an online or written health survey found that 79 (7.6%) were predicted to have vulvodynia; 28 (2.7%) met criteria for vulvodynia, but the pain had resolved; and 543 (52.3%) were asymptomatic and had no history of vulvar pain lasting 3 months or more (controls). The remaining 387 (37.3%) either reported pain with intercourse or a history of vulvar pain that did not meet criteria for vulvodynia or vulvodynia in remission. A subset of women predicted to have vulvodynia or to be asymptomatic controls were seen for a confirmatory office visit (history and examination); the reliability and validity of the survey for predicting these diagnoses was found to be excellent (Cohen’s κ=0.86 and 0.78, respectively).8
Two years after the initial study we attempted to recontact the women to assess their clinical status. All women with e-mail addresses were sent an e-mail invitation that was linked to the online survey (SurveyMonkey.com, Portland, OR). The survey had 123 questions, of which 83 were answered by all women, with the remainder answered only by those with vulvar pain. The questions consisted of multiple-choice, fill in the blanks, Likert scales, skip logic, and matrices as appropriate. A second invitation and survey were sent 3 weeks after the initial survey. A written invitation and survey were mailed to each woman without an e-mail address as well as to those returned as undeliverable by e-mail, with a reminder sent 1 month later. The online results were downloaded to an Excel file and transferred to SPSS 14.0 for Windows (SPSS Inc., Chicago, IL), whereas the written survey answers were entered, verified (under the direction of D.W.G.), and merged to the SPSS file.
Descriptive statistics were calculated for all pertinent variables. Diagnostic categories were created using previously validated criteria for active vulvodynia, vulvodynia in remission, control status, and other (pain with intercourse or vulvar pain not meeting criteria for vulvodynia).8 To estimate incidence and remission rates, further analysis was confined to those at enrollment who were diagnosed as having vulvodynia or vulvodynia in remission, or as being an asymptomatic control. Comparison of diagnoses at baseline and at 2-year follow-up was made using the McNemar test and Cohen’s κ statistic. We used t tests, χ2 analyses (using Fisher exact test when applicable), and logistic regression to assess factors associated with incidence or remission of vulvodynia as predicted by the survey.
In the fall of 2006, 843 e-mail invitations were sent to participants from the initial 2004 study that had given us e-mail addresses. Of these, 157 (18.6%) were returned as undeliverable; completed surveys were received from 454 (66.2%) of the remainder. A letter of introduction and the written survey were then mailed to nonrespondents and to those without known e-mail addresses. Of 583 written surveys sent, 40 (6.9%) were returned as undeliverable. Of the remaining 543, 290 (53.4%) were completed and returned. The overall response rate was 74.6% ([454 online+290 written]/997 potential participants).
Table 1 shows differences between respondents and nonrespondents. Respondents were more likely to be older, married, and white and to have higher formal education and higher household income levels, although race and marital status were not significant when all five variables were entered into the model.
At the initial enrollment in 2004, the prevalence of active vulvodynia, vulvodynia in remission, and asymptomatic controls were 7.6%, 2.7%, and 52.3%, accounting for 649 of the 1,037 enrollees (62.6%). The remaining other women consisted of those with a history of painful intercourse but not vulvar pain (7.5%), those with past vulvar pain but not lasting 3 months in duration (28.1%), and those reporting no intercourse but also no vulvar pain (1.5%).
Of the 744 respondents in the 2-year follow-up, 20 women (2.7%) did not complete the entire survey and were missing critical information about the presence of vulvar pain, leaving 724 women for analysis for clinical status. Using the same diagnostic criteria validated at the initial enrollment, the prevalence of active vulvodynia, vulvodynia in remission, asymptomatic control status, or “other” at the 2-year follow-up was 9.4%, 3.0%, 58.7%, and 28.9%, respectively (Fig. 1, P<.001). The 210 (28.9%) women in the “other” category were composed of two subgroups: 7.5% (54 women) who reported pain with intercourse during the past 6 months but no vulvar pain and 21.4% (155 women) who reported vulvar pain but did not meet criteria for vulvodynia (past or present), such as having pain for at least 3 months.
To estimate incidence and remission rates, we evaluated women who had been classified as cases (active or in remission) or asymptomatic controls at the baseline evaluation. We found a substantial number of women had changed diagnostic groups (P<.001 based on McNemar’s χ2 test) within the 2-year follow-up period, with a low κ statistic of 0.35 (95% confidence interval [CI] 0.29–0.41), as shown in Figure 2.
To estimate the incidence of vulvodynia among women over the 2-year follow-up period, we evaluated the 372 women at follow-up who had been asymptomatic controls at enrollment (no current pain with intercourse and no history of vulvar pain lasting 3 months or greater). Of these, 13 (3.5%, 95% CI 1.6–5.4%) had developed vulvodynia since enrollment, including nine (2.4%) women who now reported pain consistent with vulvodynia (current vulvar pain lasting 3 months or more) and four (1.1%) who reported such pain that had since resolved (Fig. 2).
Characteristics of incident cases (active or now in remission, n=13) compared with those who were still asymptomatic controls at follow-up (n=296) are shown in Table 2. Women who had been asymptomatic at enrollment and who were no longer asymptomatic but did not meet criteria for vulvodynia (vulvar pain lasting at least three months in duration) were not included in this analysis. In the univariable analysis, incident cases were younger, were more likely to have been on oral contraceptives or hormone therapy at enrollment, and were more likely to have had pain after intercourse in the past (although not meeting criteria for vulvodynia previously), compared with those who remained asymptomatic. When controlled for age, the only factor that was still statistically significant was having reported a history of pain after intercourse in the past.
Forty-five women who had been diagnosed with vulvodynia, based on the enrollment survey, completed follow-up surveys. Of these, 10 women (22.2%, 95% CI 10.1–34.4%) reported remission or lack of symptoms at follow-up. These numbers are small; hence, only very substantial differences in associated risk factors would be expected to reach a statistically significant difference at P<.05 in this study. The same characteristics listed in Table 2 were assessed among those who did and who did not have a remission over the 2-year follow-up period. Those statistically associated with going into remission included decreased reporting of pain after intercourse at enrollment (50.0% compared with 82.4%, OR (adjusted for age) 0.2, 95% CI 0.0–0.9), and a lower level of worst vulvar pain in the past 6 months reported at enrollment (mean±standard deviation 2.8±1.9 compared with 4.0±1.2 on a 0–5 pain scale, OR 0.6 (adjusted for age), 95% CI 0.4–0.9).
The use of strict criteria for vulvodynia and for asymptomatic control status increases the validity of the diagnoses made, and hence these criteria were used for this study. However, there were subgroups at enrollment and at the 2-year follow-up who did not meet criteria for either active vulvodynia, vulvodynia in remission, or asymptomatic controls. These were designated the “other symptoms” group, and comprised 37.4% of the enrollment group and 28.9% of the 2-year follow-up group. We did not include these women in the analyses of the remission and incidence rates because they did not comprise a well-defined group. However, several points regarding this subgroup deserve mention. Of those with reliable diagnoses at enrollment, substantial numbers fell in the “other symptoms” subgroup at the 2-year follow-up, having some dyspareunia or vulvar pain, but not meeting criteria for the diagnosis of vulvodynia at that time. These included 28.9% of those who had had vulvodynia at enrollment, 11.1% of the vulvodynia in remission initial group, and 16.9% of those who had been asymptomatic controls (Fig. 2). Similarly, among those who had been classified as “other symptoms” at enrollment, 10.2% now met criteria for vulvodynia (8.5% active vulvodynia, and 1.7% vulvodynia in remission)—a potential incidence rate that is greater than that noted among those who were asymptomatic at enrollment.
Estimates of the prevalence of vulvodynia have varied, depending on the study design and the population assessed. Early estimates suggested 15% of women seen in a gynecologist’s practice reported pain with intercourse and had a positive cotton-swab sensitivity at the introitus, suggesting vulvodynia.5 A community-based survey suggested 12% of women reported any chronic burning, knife-like or sharp pain, or pain on contact that lasted for at least 3 months, and 6.6% reported persistent genital burning or itching.9 A Web-based survey of 994 women, using stricter criteria, suggested 1.3% of women had ongoing vulvodynia and 1.7% reported past symptoms.7 Finally, the previously reported initial survey of the women in this study that included in-office verification of the predictive accuracy of the survey-based diagnoses in a subset indicated a prevalence of 7.6% active vulvodynia and 2.6% vulvodynia in remission.8 However, the cross-sectional design of these studies allowed prevalence estimates only, leaving the question of incidence and remission rates unanswered.
We found prevalence rates of active vulvodynia, vulvodynia in remission, and asymptomatic controls in our 2-year follow-up study to be within a few percentage points of those at initial enrollment. However, there were substantial changes in diagnostic classifications of the women (P<.001). Of those classified initially as asymptomatic controls, 3.5% (n=13) had developed classic symptoms of vulvodynia, and 2.2% had ongoing symptoms at 2 years. If this incidence rate is confirmed in larger, more diverse, population-based studies, this would indicate that there are more than one million new cases of vulvodynia per year in the United States.
Vulvodynia was traditionally considered a chronic pain disorder, with symptom remission considered rare. Recent surveys of non–clinic-based populations indicate a substantial proportion of women who reported past vulvodynia symptoms indicate the symptoms have resolved.6,7 This study documents not only reported remission of symptoms in a substantial proportion of women with validated vulvodynia but also the recurrence of symptoms among some women previously reporting resolution, suggesting vulvodynia may wax and wane over time (Fig. 2).
Women who do not meet strict criteria for vulvodynia, yet have symptoms of dyspareunia or vulvar pain, have typically not been included in studies of vulvodynia. The results from both the enrollment portion of the study and this follow-up study suggest this is a sizable subgroup. Other disease entities, such as hypertension and diabetes, have similar “borderline” subgroups, from which important information about risk for progression to disease status (or remission to a “nondiseased” asymptomatic status) might be obtained. Future study of this subset is needed to add further to our understanding of possible “predisease” states, to allow potential refinements of the diagnostic criteria, and to increase our understanding of risk factors for incident vulvodynia and remission.
There continues to be controversy regarding the role of oral contraceptive use and vulvodynia, with some studies suggesting no effect1,10 and others suggesting a possible relationship.11–15 In cross-sectional studies of women with and without vulvodynia, early age at first use of oral contraceptives has been associated with an increased risk of vulvodynia (ORs 11 and 9),11,13 as has longer duration of oral contraceptive use13,15 and use of low estrogenic contraceptives.13 Furthermore, Bohm-Starke, et al12 demonstrated that oral contraceptives are associated with increased pain sensitivity to mechanical (pressure) stimulation at the vulva in normal women, with maximal sensitivity noted at the posterior introitus—the area typically most sensitive among women with vulvodynia. We found in this study that taking either oral contraceptives or hormone therapy at enrollment was associated with incident vulvodynia only in the univariable analysis, yet not when controlling for age at enrollment. This reflects the finding that younger age was associated with incident disease in this study and that younger age and use of oral contraceptives or hormone therapy are similarly associated (P<.001, data not shown). The size of this study lacks the power to fully assess such risk factors in detail.
Pain that follows intercourse was associated with an increased risk of incident vulvodynia (OR more than 10) as well as a decreased probability of vulvodynia remission (OR=0.2) in this study, and this finding persisted when controlling for age. This prolonged pain is similar to the common finding noted in the clinical setting in which women with positive cotton-swab tenderness continue to experience pain at the introitus after this testing for vulvar hypersensitivity. The presence of this symptom before onset of chronic vulvar pain suggests an identifiable predisposition to vulvodynia that might lead to the identification and implementation of preventive measures.
Limitations of this study exist. The enrollment of women from the University of Michigan’s Women’s Health Registry, although nonselected for women with health problems, might not be representative of the population at large. Further study in a population-based cohort, with an increased representation of women from various ethnic minorities, is needed. Furthermore, although the initial enrollment of women was accompanied by in-office evaluation of a subset to determine the validity and reliability of the reported symptoms and diagnosis, we used the same criteria but did not repeat the validation component in this follow-up. We did not obtain listings of current medications, and hence, some women reporting remission may have been on medications that decrease vulvodynia symptoms. However, complete lack of symptoms would not be expected in most of these women, and hence, the degree of error based on ongoing treatment would be expected to be small. Finally, greater numbers of women are needed to increase the power of the study to assess risk factors that might not be identifiable in this project.
In conclusion, the annual rates of new onset vulvodynia among asymptomatic controls, and of remission of symptoms among women with known vulvodynia, are sizable, at 1.8% and 11.1%, respectively. Presence of a history of pain after intercourse was positively associated with incident vulvodynia and was negatively associated with remission of symptoms.
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