Introduction

Vulvodynia is a chronic pain disorder of the vulva, occurring in the absence of relevant findings or a specific clinically identified neurologic disorder. Vulvodynia is estimated to affect 8-15% of women and has been described as the leading cause of dyspareunia in women age <50 years. Symptoms of vulvodynia may include stinging, burning, irritation, or itching. The etiology of vulvodynia is unknown, and likely multifactorial.

In 2015, a consensus vulvar pain terminology committee redefined vulvodynia as vulvar pain of at least 3 months’ duration, without clear identifiable cause, which has potential associated factors ( Table 1 ). A key objective of the new terminology introduced in 2015 was to identify potential factors associated with vulvodynia, such as genetic or hormonal factors, inflammation, musculoskeletal or neurological mechanisms, neuroproliferation, and psychosocial or structural issues. The recognition of these factors in a given patient could be used to assist in developing individualized treatment plans. For example, those women with a perceived neuropathic etiology might benefit from tricyclic antidepressants or gabapentin, whereas those with musculoskeletal factors might respond better to pelvic floor physical therapy.

Provoked vestibulodynia (PVD), the most common subset of vulvodynia, is localized to the vaginal vestibule (entry to the vagina, including the introitus, and extending to the hymenal ring) and presents only with contact, such as from tampon insertion or intercourse. Diagnosis of PVD is based on history, physical exam (which excludes other pathology), and a positive cotton swab test, whereby pain is elicited when the vestibule is gently touched with a cotton swab at the 2-, 4-, 6-, 8-, and 10-o’clock positions. Complete evaluation should also include palpation of the levator muscles immediately inside the vagina. Pelvic floor dysfunction with hypertonicity and pain has been demonstrated in PVD patients vs controls.

Association of vulvodynia with fibromyalgia (FMS) is well documented. FMS is a syndrome of unknown etiology, associated with chronic widespread musculoskeletal pain. FMS is diagnosed by history, absence of other identified pathology, and the presence of pain in 11 of 18 specified tender points on physical exam (tender point tenderness [TPT] exam) ( Figure 1 ). In 2010, an alternative diagnostic criterion for FMS that did not require TPT examination was developed and subsequently validated. Investigators and clinicians still disagree on the utility of the TPT exam.

Tender point tenderness diagrammatic scheme

This schematic defines the tender points examined in determining a diagnosis of FMS. The American College of Rheumatology guidelines suggest that people with fibromyalgia will have pain in at least 11 of these tender points when a doctor applies a certain amount of pressure.

Phillips et al. Relationship between tender point tenderness and vaginal algometer pain intensity. Am J Obstet Gynecol 2016 .

The vaginal algometer is a device developed by researchers to assess pain deeper in the vagina than could be evaluated with the cotton swab test. The device consists of a probe containing a pressor sensor that is inserted into the vagina and a measurement circuit that converts the signal from the probe into a force measurement, with a resultant threshold value. The vaginal algometer was originally intended to measure pressure pain threshold (PPT) over the lateral walls of the vagina, over the area of the pudendal nerve, but has been subsequently validated in women without pain in vaginal sites including the pubococcygeus and iliococcygeus muscles, and the anterior and posterior vaginal wall. The intravaginal algometer has also been shown to assess muscle PPT independently of mucosal pain in women with vulvodynia.

The vaginal algometer may be considered a TPT examination of the vagina. In this regard, the objective of this study was to correlate ratings of pain intensity during the nongenital TPT examination to ratings of pain intensity with the intravaginal algometer in women with PVD, and to determine whether subjects with PVD and nongenital TPT scores consistent with the diagnosis of FMS had higher pain intensity scores with the vaginal algometer compared to those without FMS.

Materials and Methods

Women included were enrolled in a multisite, randomized, double-blind, placebo-controlled crossover study of extended release gabapentin in the treatment of PVD. Institutional review board approval was obtained at all 3 study sites: the University of Tennessee Health Science Center, Rutgers Robert Wood Johnson Medical School, and the University of Rochester Medical Center ( clinicaltrial.gov ). Women were enrolled in the study if they were age >18 years; had >3 continuous months of insertional dyspareunia, pain to touch, or pain with tampon insertion (modified Freidrich criteria for vulvodynia); and demonstrated an average score of ≥4 on the 11-point tampon test (0 = no pain at all; 10 = worse pain ever) during the 2-week screening period.

Exclusion criteria included: (1) other vulvar conditions or active infections identified clinically or by a positive Affirm VPIII microbial identification test (BD Molecular Diagnostics, Franklin Lakes, NJ); (2) a prior vestibulectomy; (3) pregnant or at risk for pregnancy and not using a reliable contraceptive for 3 months prior to and during the study; (4) a major medical or psychiatric condition, including substance abuse; (5) a score of ≥12 on the hospital anxiety and depression scale, indicating a major depressive episode ; (6) use of centrally acting medications, excluding selective-serotonin receptor inhibitors; and (7) use of topical lidocaine.

At the screening visit, an interviewer-administered questionnaire collected detailed subject demographic data and a complete medical and gynecological history, including current medications. A visual inspection of the vulva, speculum exam, and bimanual pelvic exam were performed. A cotton swab test was used to clinically confirm PVD, an Affirm test collected, and a Rakoff stain evaluated to determine vaginal estrogen status. If the Affirm test was positive for yeast, Gardnerella , or trichomonas, the patient was treated and rescreened. If the Rakoff stain showed >10% parabasal cells, patients were treated with local estrogen, if appropriate, and rescreened after 6 weeks. Nongenital TPT and intravaginal algometry was performed at a separate visit, only after screening criteria were met.

TPT was performed by using the thumb pad of the dominant hand to apply 4 kg of pressure in a perpendicular direction for 4 seconds to 18 tender points. Vaginal pain sensitivity was measured using a prototype intravaginal pressure algometer, where 0.1, 0.3, and 0.5 kg/cm ² forces were applied digitally in random assignment by force and location to the right and left iliococcygeus muscle regions and the posterior vaginal wall, for a total of 9 data points. Both TPT and algometer pain intensity were reported on a 0 (no pain) to 10 (worse pain) numeric rating scale (NRS). A diagnosis of FMS was made if pain was present (NRS >1) in at least 11 of the tender point sites.

Correlations were computed between the composite pain intensity of TPT and those of iliococcygeus regions and the posterior vaginal wall. Composite scores were calculated by totaling the NRS at individual nongenital TPT, and for intravaginal algometry by totaling the NRS from the right and left iliococcygeus muscle. Independent t tests were used to determine differences in iliococcygeus regions and the posterior vaginal algometer pain intensity ratings and presence or absence of FMS. The significance level was at P < .05 and the data were expressed as mean ± SD.