Vaginal erbium–YAG laser is a novel treatment for vaginal atrophy, which is currently known as GSM. Literature showed the effectiveness and safety of intravaginal laser therapy, while erbium–YAG laser is considered as a safer option as compared with fractional CO2 laser because of its non-ablative effect [4,5,6,7,8].

The mechanism of action of erbium–YAG laser is its photothermal effect on the vaginal epithelium, which causes superficial tissue shrinkage, neovascularization, and neocollagenesis, resulting in vaginal tissue thickening, and increases vaginal elasticity [4].

Based on the literature, few studies have reported an improvement of vaginal atrophy symptoms after vaginal erbium–YAG laser treatment [6,7,8]. However, no study has been conducted on vaginal erbium–YAG laser and vaginal lactobacilli, which can be used as an objective measurement. Vaginal lactobacilli are vaginal normal flora that dynamically changed with vaginal maturation, and they play a role in maintaining vaginal acidity and compete with pathogens [9, 10, 12].

To our knowledge, this study is the first randomized sham-controlled study to assess the effect of vaginal erbium–YAG laser on vaginal lactobacilli, vaginal pH, and vaginal atrophy symptoms. This study reports the objective and subjective measurements of vaginal atrophy after vaginal erbium–YAG laser treatment. The results show an increase of vaginal lactobacilli grading after two laser applications. The increase of vaginal lactobacilli grading can be described by the effect of vaginal laser on vaginal epithelial maturation, that is, superficial cells of the vaginal epithelium are increased after treatment with vaginal laser. The superficial cells are glycogen-rich cells, and lactobacilli use glycogen as their nutrients and produce lactic acid. Moreover, vaginal atrophy symptoms assessed by VAS and vaginal atrophy scores were improved after laser treatments. The reduction in VAS score in this study is similar to the results of previous studies [5,6,7,8, 13,14,15]. However, compared with several reports,[9, 16] no statistically significant difference in vaginal pH before and after vaginal laser applications is observed in this study. This result can be due to the majority of participants with grade 1 vaginal lactobacilli after vaginal laser treatment. Their vaginal epithelium contains only few lactobacilli that cannot produce enough lactic acid to lower vaginal pH.

A recent large prospective observational study of fractional CO2 laser conducted in Italy has shown a significant improvement of vaginal lactobacillus species at four weeks after CO2 laser treatment [17]. This study also demonstrates the improvement of vaginal atrophy symptoms indicated by the most bothersome symptoms. However, compared with the result of our study, a significant improvement in vaginal pH was observed after the treatment. This result can be explained by the differences in laser energies and percentage of participants with lactobacillus-predominated vaginal wet smear.

The safety of intravaginal laser therapy is a major concern. The result from previous studies showed only few minor adverse events after vaginal laser application [5, 8, 16, 18] In our study, only one patient in the sham group complained about pain after treatment, which was improved during the follow-up period. In addition, no side effects were reported after treatment in the laser group. Therefore, the safety result from our study is concordant with previous studies,[5, 8] confirming the short-term safety of vaginal erbium–YAG laser treatment. However, long-term follow-up is necessary to evaluate the long-term safety of this treatment.

This study has several strengths. First, this study has a randomized sham-controlled design, which can diminish the bias and placebo effect. Second, our study evaluates the subjective (VAS score) and objective (vaginal lactobacilli, vaginal pH, and vaginal atrophy score) outcomes of vaginal atrophy after vaginal laser treatment.

However, this study also has a limitation, which is the different baseline characteristics between the laser group and sham group (participants in the laser group were younger that those in the sham group), which results from imperfect randomization. Moreover, the age difference between groups can have an impact on vaginal lactobacilli grading. Therefore, the main findings of this study were the improvement of vaginal atrophy symptoms and vaginal atrophy score after the vaginal laser treatments.

Another limitation of our study was lacking an active control group (such as vaginal estrogen, vaginal lactobacilli, or other non-hormonal treatments). Thus, for clinical implication, clinicians should be acknowledged this limitation. However, as this study showed the improvements of vaginal atrophy after the vaginal erbium laser procedure, it might lead to further clinical trials with an active control group.

A significant number of participants were lost to follow-up during the study period because of the COVID-19 situation and personal illness that is not related to the procedure. However, the number of participants who were lost to follow-up was similar in the laser and sham groups (2/22 and 3/22, respectively). Therefore, the effect of loss to follow-up might not interfere with the outcome of this study.

For further research, increasing the sample size or vaginal laser applications might show a statistically significant improvement of subjective and objective measurements of vaginal atrophy after vaginal erbium laser treatment. Moreover, further research may focus on the possible benefits of the vaginal erbium laser in other study populations such as menopause women after ovarian tissue cryopreservation and transplantation or patients with refractory lower urinary tract dysfunction [19, 20].

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