Botulinum Toxin a for Provoked Vestibulodynia: 12 Months' Follow-Up of a Randomized Controlled Trial

BACKGROUND

Provoked vestibulodynia (PVD) is a common pain disorder afflicting primarily young women, and botulinum toxin A (BTA) has been to a limited extent tested as a treatment.

AIM

Evaluate outcome 12 months after injection with BTA as a treatment for PVD.

METHODS

We conducted a double-blinded, placebo-controlled trial of twice repeated injections of 50 units of BTA or placebo in the bulbocavernosus muscles, 3 months apart, in women with PVD. Treatment outcome after six months', failed to show any significant difference in pain reduction between the groups, as previously reported. Here, we report treatment outcomes 12 months after the first injections. In addition to injections, participants where instructed to perform pelvic floor exercises during month 6-12. 38 participants/group was calculated to achieve a statistical power of 80% based on an effect size of 20 VAS units (mean score range 56-76±31 SD).

OUTCOMES

Primary outcome was self-reported dyspareunia or pain at tampon use, using a visual analogue scale (VAS) 0-100. Secondary outcomes were vaginal pressure measurements, psychological health, sexual function and distress.

RESULTS

From the initial 88 randomized women with PVD, 75 remained at 12 months; 38 in the BTA and 37 in the placebo group. There was no significant difference in primary outcome between the groups. Vaginal pressure in the BTA group had been restored to pre-treatment levels, with no differences between the groups at 12 months. There was an increase in sexual function in the BTA group, with a Female Sexual Function Index of 22.8 (±4.8) compared to the placebo group to 19.7 (±5.0), P=.048. No differences were observed in sexual distress, stress and anxiety. There was an increase in number of women attempting intercourse in the BTA group (74%) compared with placebo (43%), P=.005. Too few patients performed the pelvic floor exercises for this intervention to be analyzed.

CLINICAL IMPLICATIONS

This study highlights BTA as a safe treatment option for patients with PVD.

STRENGTHS AND LIMITATIONS

The randomized, double-blinded design and repeated treatments are the major strengths of this study and it is the first study to objectively evaluate muscular effect after BTA injections. The major shortcoming is that few participants performed the pelvic floor exercises, preventing analyses.

CONCLUSION

At 12 months' follow up, no significant difference in reduction of dyspareunia or pain at tampon use was observed. Women receiving BTA attempted intercourse more often and improved their sexual function compared with women receiving placebo.

A118G polymorphism in the μ-opioid receptor gene and levels of β-endorphin are associated with provoked vestibulodynia and pressure pain sensitivity

Background and aims

Provoked vestibulodynia (PVD) is the most common cause of dyspareunia among young women. The aetiology is largely unknown and treatment is often extensive and longstanding with varying outcomes. Patients display general pain hypersensitivity and there are correlations with other chronic pain syndromes such as fibromyalgia later in life. The A118G polymorphism in the μ-opioid receptor (OPRM1) gene influences endogenous pain regulation and pain sensitivity, but has not been studied in this patient group before. We aimed to investigate a possible association between A118G polymorphism and PVD, with correlation to plasma levels of β-endorphin, and to explore relationships between this polymorphism and pain sensitivity among women with PVD and healthy controls.

Methods

This case-control study included 98 women with PVD and 103 controls. Participants filled out study-specific questionnaires and underwent quantitative sensory testing of pressure pain thresholds on the arm, leg and in the vestibular area. Levels of β-endorphin were analyzed by radioimmunoassay using the EURIA-beta-endorphin kit, and the A118G single-nucleotide polymorphism (SNP; rs1799971) in the OPRM1 gene was analyzed using the TaqMan SNP genotyping assay.

Results

The 118G allele was more common in controls (44%) than in patients (30%) (p = 0.042). The odds ratio of having PVD was 1.8 in participants carrying the 118A allele compared to participants hetero- or homozygous for the 118G allele (OR = 1.846, CI: 1.03-3.31, p = 0.039). Pressure pain thresholds on the leg were higher for participants carrying the 118G allele (mean 480 kPa, SD 167.5) than for those carrying the 118A allele (mean 419, SD 150.4, p = 0.008). Levels of β-endorphin were higher in patients (mean 17.9 fmol/ml, SD 4.71) than in controls (mean 15.8 fmol/ml, SD 4.03) (p < 0.001).

Conclusion

We found an association between the A118G polymorphism in the OPRM1 gene and an increased risk of PVD and increased pain sensitivity among participants carrying the 118A allele. PVD patients were more sensitive to pressure pain and had higher levels of plasma β-endorphin than controls. The results indicate that differences in endogenous pain modulation involving the opioid system could contribute to the pathophysiology of PVD and the general pain hypersensitivity seen in these women.

Implications

The data support the conceptualization of PVD as part of a general pain disorder with a possible genetic predisposition. The age of onset of PVD is usually between 18 and 25 years and already at this age general pain hypersensitivity is present but rarely causing disability. We believe that early recognition and treatment, with the risk of further development of chronic pain taken into consideration, might prevent future aggravated pain problems in this patient group.

GCH1-polymorphism and pain sensitivity among women with provoked vestibulodynia

Background

Provoked vestibulodynia (PVD) is a pain disorder localized in the vestibular mucosa. It is the most common cause of dyspareunia among young women and it is associated with general pain hypersensitivity and other chronic pain conditions. Polymorphism in the guanosine triphosphate cyclohydrolase (GCH1) gene has been found to influence general pain sensitivity and the risk of developing a longstanding pain condition. The aim of this study was to investigate GCH1-polymorphism in women with PVD and healthy controls, in correlation to pain sensitivity.

Results

We found no correlation between the previously defined pain-protective GCH1-SNP combination and the diagnosis of PVD. Nor any correlation with pain sensitivity measured as pressure pain thresholds on the arm, leg and in the vestibule, coital pain scored on a visual analog scale and prevalence of other bodily pain conditions among women with PVD (n = 98) and healthy controls (n = 102). However, among patients with current treatment (n = 36), there was a significant interaction effect of GCH1-gene polymorphism and hormonal contraceptive (HC) therapy on coital pain (p = 0.04) as well as on pressure pain thresholds on the arm (p = 0.04). PVD patients carrying the specified SNP combination and using HCs had higher pain sensitivity compared to non-carriers. In non-HC-users, carriers had lower pain sensitivity.

Conclusions

The results of this study gave no support to the hypothesis that polymorphism in the GCH1-gene contributes to the etiology of PVD. However, among patients currently receiving treatment an interaction effect of the defined SNP combination and use of hormonal contraceptives on pain sensitivity was found. This finding offers a possible explanation to the clinically known fact that some PVD patients improve after cessation of hormonal contraceptives, indicating that PVD patients carrying the defined SNP combination of GCH1 would benefit from this intervention.