Sexual Inhibition and Sexual Excitation in Erectile Dysfunction

Abstract

Erectile dysfunction (ED) is a common problem with many aetiologies. The development of phosphodiesterase type 5 inhibitors (PDE5Is) has offered a highly efficacious therapeutic approach to the treatment of ED. However, a significant number of men fail to respond to medication, and others discontinue its use despite good therapeutic responses. Little is known about the determinants of low PDE5I efficacy or compliance. It is recognised that adequate sexual arousal is necessary in order for PDE5Is to have an effect, but arousability is rarely assessed during the routine therapeutic workup. It is therefore possible that unidentified low arousability contributes to therapeutic failure. The Dual Control Model of Sexual Response offers a theoretical framework for the investigation of sexual excitation and inhibition (which may impact on arousability) that can be undertaken using its associated questionnaire, the sexual excitation/sexual inhibition questionnaire (SIS/SES). The purpose of the studies reported in this thesis was to evaluate how the propensities of sexual excitation and inhibition relate to ED sufferers response to PDE5I therapy. The studies focused on men being treated by general practitioners for apparent psychogenic ED. Four studies were conducted. In the first study, the aim was to investigate whether individual differences in the propensity for sexual inhibition and excitation measured using the SIS/SES questionnaire predicted responses to PDE5Is. The study was based on the hypothesis that men with lower arousability, operationalized as low excitation, would be less responsive to PDE5I then men with higher excitation. Men aged 18 and older (N = 100) who were prescribed PDE5Is for the first time were recruited into the study and assessed at baseline and 3 months as part of their normal course of care. The severity of ED was assessed using the erection function (EF) scale of the International Index of Erectile Function (IIEF), and sexual inhibition and excitation were measured using the SIS/SES questionnaire. The results of this study showed that higher SES and IIEF-EF scores at the beginning of therapy were predictive of a larger improvement in IIEF-EF score in response to therapy. Sexual inhibition scores were not predictive of changes in IIEF-EF scores. The findings suggest that an individual’s propensity for sexual excitation influences their response to PDE5I therapy. In the clinical setting, evaluation of the propensity for sexual excitation may help practitioners determine which of the treatment options available is most likely to have the best result. It is possible that men with lower SES scores should receive PDE5Is at the highest possible dose. The second study evaluated whether the ongoing failure of PDE5I therapy to improve erectile function had an adverse impact on sexual excitation and/or inhibition, and therefore decreased the likelihood of a successful response in the future. Established PDE5I users completed the SIS/SES questionnaire at recruitment and three months later. On the basis of IIEF scores at recruitment, subjects were divided into two groups according to the severity of their ED - mildly affected (M) and mild – moderately affected (MM). SES scores were significantly lower, and SIS1 scores significantly higher in Group MM at recruitment and at three months (P < 0.001). In Group M, SES scores increased (P < 0.005) and SIS1 (P < 0.001) and SIS2 (P = 0.01) scores decreased over the three months of the study. In Group MM, SES scores decreased while SIS1 scores increased over the study period (P < 0.001). The results for Group M showed that men whose EF scores increased were more likely to experience increased SIS2 and decreased SES scores. Analysis of the results using multiple linear regression showed that SIS/SES variables were of little value in predicting erectile function (EF) at recruitment, or change in EF during the study period. This was an unexpected finding, because previous studies have consistently shown a link between SIS1 and IIEF-EF scores. It is possible that sexual excitation and inhibition, although fundamentally traits, may also be influenced by the current state of the patient. The findings of this study suggest that the severity of ED in non-responders influences how the state component of measured excitation and inhibition changes over time, with more severely affected patients experiencing changes that decrease the likelihood of a successful response to PDE5Is in the future. The third study built on the finding reported by Lykins et al (2012) that couples’ similarities in sexual excitation and inhibition predict sexual function in men who were not experiencing clinical ED. The aim was to investigate whether the degree of between-partner similarity or dissimilarity in the propensity for sexual inhibition and excitation in heterosexual couples (N = 189) predicted the severity of ED in patients who had sought treatment for ED. The severity of ED was assessed using the erection function domain of the International Index of Erectile Function (IIEF-EF), and sexual inhibition and excitation were measured, in both men and women, using the SIS/SES questionnaire. Regression analyses showed that men (ß = -0.21, t = -2.9, P = 0.004) and women’s SIS1 scores (ß = -0.42, t = -6.2, P = 0.001), and couple similarity in SES scores (ß = 0.19, t = 3.0, P = 0.002), were significant predictors of IIEF-EF score, and that couple similarity in SIS1 scores negatively predicts IIEF-EF, meaning better erectile function. In other words, lower SIS1 scores at baseline predicted a higher erectile function score on the IIEF-EF. In the fourth study, the aim was to determine whether sexual excitation and inhibition influenced patients’ expectations of the therapeutic response to PDE5Is, and whether those expectations were predictive of the actual therapeutic response. A questionnaire was developed and used to collect data on expectations in eighty men commencing PDE5I therapy, and after three and six months of treatment. At the same time, subjects completed the IIEF, SIS/SES and Beck’s Depression Inventory (BDI). SIS/SES scores were not predictive of scores of any items on the expectations questionnaire, nor was there any evidence of an effect on expectations on changes in IIEF or BDI scores. Although changes in IIEF and BDI scores from recruitment to 3 months were indicative of improved sexual function and less depression, scores on items on the expectations scale decreased, suggesting that expectations were not being met. The items for which scores decreased were the expectation to be prescribed a drug, that the drug would restore the sexual function to normal, would work within 30 minutes of administration, improve patients confidence to engage in sexual activity, and that the medication was the best treatment for ED across the three data collection points. The findings of the study suggested that the education of patients about how PDE5Is should be used was sub- optimal. The findings of these studies suggest that the measurement of sexual inhibition and excitation can provide some information that may be of use in planning PDE5I therapy. Specifically, the capacity to predict the response to medication may enable clinicians to create more realistic expectations in their patients, and therefore decrease the risk of dissatisfaction and discontinuation. If men with low arousability can be identified, it may be possible to implement counselling strategies to address the problem and improve the likelihood of therapeutic success. This concept can be extended to partners, given that these studies have shown that partner similarities predict some of the therapeutic response to PDE5Is.