Chronic vulvar pain in a cohort of post-menopausal women: Atrophy or Vulvodynia?

This study used data from the Michigan site of SWAN, a multiethnic prospective cohort
study addressing health-related changes in the midlife and menopausal transition.
The cohort has been described in detail previously 10]. Briefly, in 1996, each SWAN clinic site enrolled white women and one targeted minority
population. The Michigan SWAN population, established using a community census, was
composed of women aged 42–52 years at baseline, who were not using exogenous hormones
at the time of enrollment, had an intact uterus and at least one ovary and had had
a menstrual period in the three months before enrollment, were not pregnant or lactating,
and self-identified as either white or African American. At baseline and each follow-up
visit a blood sample was collected, height and weight measures were taken while demographic
characteristics, medication use, and symptoms of vaginal dryness were ascertained
by questionnaire. Over the next 17 years women participated in follow-up visits approximately
annually. At the 13th follow-up visit in 2012, the Michigan site added several screening
instruments for chronic pain conditions including a validated screening instrument
for vulvodynia 11].

At baseline, the Michigan SWAN cohort was composed of 543 women, 60 % of whom were
African American by design. In 2012, 32 (5.9 %) women had died and 411 (80.4 % of
the non-deceased cohort) were still active, 380 (92.5 %) of whom participated in follow-up
Visit 13. Nine women who did not answer any questions pertaining to vulvar pain were
excluded, leaving 371 womeN (61.7 % African American) eligible for this analysis. For analyses including endogenous
serum hormone levels, we evaluated hormone levels at Visit 12, to ensure hormone levels
preceded the report of vulvar pain status at Visit 13. These analyses include 319
women as we excluded the 37 women who did not have blood drawn and the 15 women who
reported HT use at Visit 12.

Ethics and consent

This study was approved by Health Sciences and Behavioral Sciences Institutional Review
Board of the University of MichigaN (HUM00083308). Women provided informed consent at baseline and each follow-up interview.

In Visit 13, Michigan participants completed a validated screening questionnaire for
vulvodynia 11] that obtained information on symptoms of vulvar pain or discomfort, including date
of pain onset, duration of pain, and whether pain continues. We interpret a positive
screen in this postmenopausal population to be consistent with vulvodynia but acknowledge
that this screening tool may not adequately differentiate vulvodynia from atrophy
in this postmenopausal cohort. Therefore we use the term “chronic vulvar pain” in
lieu of vulvodynia when presenting the results.

Based on responses to the vulvodynia questionnaire, each participant was categorized
into one of three groups: women with current chronic (lasting 3 months or longer)
vulvar pain, women who reported ever having chronic vulvar pain in the past or reported
having short-duration (less than 3 months duration) vulvar pain symptoms, and women
reporting no current or past vulvar pain symptoms. Current chronic vulvar pain was
defined by a history of vulvar pain or discomfort at the opening to the vagina that
had lasted for at least three months and had been experienced in the preceding three
months. The past chronic vulvar pain/short-duration vulvar pain symptom group included
women who had a history of vulvar pain lasting for at least three months but who had
not experienced pain in the preceding three months and women with current vulvar pain
lasting for less than three months. This group represents a heterogeneous symptomatic
group who, based on prior work 12], are more likely than the non-symptomatic group to develop vulvodynia, and hence
we categorize them separately from the no pain group.

Age was modeled as a continuous variable. Race/ethnicity was self-reported as either
white or African American. Measured height and weight were used to calculate body
mass index (BMI) (weight in kilograms (kg) divided by height in meters (m) squared).
BMI was further categorized as normal weight, overweight, or obese (25, 25-??30,
and??= 30 kg/m
²
). Socioeconomic status was assessed by self-reported difficulty paying for basics
(very hard versus somewhat or not hard) and education at baseline (high school or
less versus at least some college). Marital status was categorized as either married
or not married.

In addition to questions about vulvar pain, we asked about other specific vulvovaginal
symptoms at Visit 13 including self-reported number of days in the past 2 weeks of
vaginal dryness, soreness, and irritation categorized into three duration levels (0 days,
1–5 days, or 6 days). In addition, we created variables to reflect whether women
ever reported vaginal dryness before, and after, the final menstrual period (FMP)
or hysterectomy (yes/no) based on responses at each follow-up visit. Although women
were not eligible to enroll in SWAN ff they were using HT, women who began using HT
after enrollment remained in the study. Two HT variables were considered: current
HT use (yes/no), and ever used HT during the study (yes/no).

At each visit, a fasting blood sample was collected, refrigerated for 1–2 h after
collection, and then centrifuged. Serum hormone levels of estradiol (E2), dehydroepiandrosterone-sulfate
(DHEA-S), follicle stimulating hormone (FSH), sex hormone-binding globuliN (SHBG), and testosterone (T) were determined.

All assays were performed on the ACS-180 automated analyzer (Bayer Diagnostics Corporation,
Tarrytown, NY) at the CLASS laboratory at the University of Michigan, utilizing a
double-antibody chemiluminescent immunoassay with a solid phase anti-IgG immunoglobulin
conjugated to paramagnetic particles, anti-ligand antibody, and competitive ligand
labeled with dimethylacridinium ester (DMAE). The FSH assay is a modification of a
manual assay kit (Bayer Diagnostics) utilizing two monoclonal antibodies directed
to different regions on the beta subunit, with a lower limit of detection (LLD) of
1.05 mIU/mL. Inter-and intra-assay coefficients of variation were 12.0 % and 6.0 %,
respectively. The E2 assay modifies the rabbit anti-E2-6 ACS-180 immunoassay to increase
sensitivity, with a LLD of 1.0 pg/mL and inter- and intra-assay coefficients of variation
averaging 10.6 % and 6.4 %, respectively. The T assay modifies the rabbit polyclonal
anti-T ACS-180 immunoassay, with a LLD of 2.19 ng/dL and inter-and intra-assay coefficients
of variation of 10.5 % and 8.5 %, respectively. The DHEA-S and SHBG assays were developed
using rabbit anti-DHEA-S and anti-SHBG antibodies, with LLDs of 1.52 mcg/dL and 1.95
nM, respectively. For DHEA-S, the inter- and intra-assay coefficient of variation
were 11.3 % and 8.0 %, respectively. For SHBG, the inter- and intra-assay coefficient
of variation were 9.9 % and 6.1 %, respectively. Duplicate E2 assays were conducted,
with results reported as the arithmetic mean for each subject, with a CV of 3-12 %.
All other assays were single determinations. Hormone levels below the lower limit
of detection were assigned a random number between 0 and the lower limit of detection.

The prevalence of vulvar symptoms overall and stratified by demographic characteristics
were calculated and compared using Chi-squared and Fisher’s Exact tests as appropriate.
Hormone levels were log-transformed for regression analyses. The median values of
the log-transformed E2, DHEA-S, SHBG, FSH, and T at Visit 12 were compared overall
and across symptoms groups using Kruskal-Wallis tests. Relative odds ratios (OR) and
95 % confidence intervals (CI) comparing the current chronic vulvar pain and past/short-duration
vulvar pain groups to the no vulvar pain group were calculated using multinomial logistic
regression models appropriate for outcomes with more than two categories 13]. These models compare odds for reporting current chronic vulvar pain symptoms in
relation to the no pain category and odds for reporting past/short-term vulvar pain
symptoms in relation to the no pain category. In addition to an unadjusted model,
models adjusted for race, BMI, and age were also assessed. Analyses were performed
using SAS 9.3 (Cary, NC).