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. Studies
18,22,23 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 studies
6-8 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 mechanical
5,10,12,13 and heat
26 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 study
7 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.