Efficacy of Transcranial Direct-Current Stimulation (tDCS) for Provoked Vestibulodynia : a Triple Blind Randomized Controlled Trial

The McGill-Melzack questionnaire allows the assessment of sensory, affective and evaluative components of pain. This world-renowned questionnaire, studied for its validity, reliability and responsiveness to change, is commonly used in RCTs (Bergeron et al., 2001; Melzack, 1975; Davidoff et al., 1987; Hays et al., 1994; Bansal et al., 2009; Moy et al., 2011; Foster et al., 2010).

A gradual pressure (1 to 1000 g) will be applied to three distinct points of the vestibule at the 3, 6 and 9 o'clock positions (Cyr et al., 2014). Each of these pressure points will be applied randomly (e.g. 3,6,9 or 3,9,6 or 6,9,3.). During this procedure, each participant will be asked to indicate when they start to feel pain (pain threshold) and subsequently the maximal pressure that can be tolerated (pain tolerance). Pain intensity is assessed throughout the test using a Computerized Visual analog scale (CoVas). This assessment has shown good reliability and validity (Cyr et al., 2014).

The Female Sexual Function Index (FSFI) is a multidimensional measure of sexual function evaluating desire, arousal, lubrication, orgasm, satisfaction and pain. In addition to good psychometric properties (reliability, internal consistency and responsiveness to change (Rosen et al., 2000; Goldfinger et al, 2009), normative data are available for this questionnaire suggesting clinical level of dysfunctions (Wiegel et al., 2005).

Pain catastrophizing will be assessed using the Pain Catastrophizing Scale (Sullivan, Bishop, \& Pivik, 1995), which consists of 13 items measuring exaggerated negative thoughts and feelings about the meaning of pain. Items are scored on a 5-point scale with the end points (0) not at all and (4) all the time. The PCS is a reliable and valid measure that has demonstrated a stable factorial structure across clinical and general populations, including a French population (French et al., 2005; Osman et al., 2000; Sullivan, et al., 1995).

Anxiety will be assessed using the Spielberger State-Trait Anxiety Inventory (STAI - (Spielberger, Gorsuch, \& Lushene, 1970); ASTA - (Gauthier \& Bouchard, 1993)). The STAI is a 40-item, well-known and widely used measure of state and trait anxiety that has demonstrated very good psychometric properties (Cronbach's alpha State = .93, Trait = .97) in various clinical and non-clinical samples including pain populations (Gauthier \& Bouchard, 1993; Greenberg \& Burns, 2003; Rule \& Traver, 1983; Tanaka-Masumi \& Kameoka, 1986).

Depression or depression symptoms will be measured with the Beck Depression Inventory-II (BDI-II). The BDI-II is comprised of 21 items, with scores for most items ranging from 0 (low intensity) to 3 (high intensity) (Beck, Steer \& Brown, 1996; Beck, Steer \& Garvin, 1988). This measure of depression has been validated for use in chronic pain populations (Turner \& Romano, 1984).

The Pain Anxiety Symptoms Scale (PASS-20), evaluating fear of pain, also shows good psychometric properties (Coons, Hadjistavropoulos \& Asmundson, 2004; McCracken \& Dhingra, 2002).

Patient self-reported improvement [scale of 0 (completely dissatisfied) to 10 (completely satisfied)] and treatment satisfaction [scale of 0 (worse) to 10 (complete cure)] will be measured at the 2-week post-treatment and 3-month post-treatment structured interview in order to assess the clinical significance of results.

Sexual satisfaction will be assessed using the Global Measure of Sexual Satisfaction scale, which consists of 5 items assessing global sexual satisfaction. Internal consistency of this scale is high (alpha = 0.90), as is test-retest reliability (r = 0.84) (Lawrance \& Byers, 1998).