Title: Clinical characteristics and penile afferent neuronal function in patients with primary delayed ejaculation
Abstract: AndrologyVolume 1, Issue 5 p. 787-792 Original ArticleFree Access Clinical characteristics and penile afferent neuronal function in patients with primary delayed ejaculation J.-D. Xia, Corresponding Author J.-D. Xia Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorY.-F. Han, Corresponding Author Y.-F. Han Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorF. Pan, F. Pan Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, ChinaSearch for more papers by this authorL.-H. Zhou, L.-H. Zhou Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, ChinaSearch for more papers by this authorY. Chen, Corresponding Author Y. Chen Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorY.-T. Dai, Corresponding Author Y.-T. Dai Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this author J.-D. Xia, Corresponding Author J.-D. Xia Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorY.-F. Han, Corresponding Author Y.-F. Han Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorF. Pan, F. Pan Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, ChinaSearch for more papers by this authorL.-H. Zhou, L.-H. Zhou Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, ChinaSearch for more papers by this authorY. Chen, Corresponding Author Y. Chen Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this authorY.-T. Dai, Corresponding Author Y.-T. Dai Department of Andrology, Nanjing Drum Tower Hospital, Nanjing Medical University, Nanjing, China Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, Nanjing, China Correspondence: Yutian Dai, Department of Andrology, Nanjing Drum Tower Hospital, Nanjing University Medical School, 321 Zhongshan Road, Nanjing 210008, China. E-mail: [email protected]Search for more papers by this author First published: 22 August 2013 https://doi.org/10.1111/j.2047-2927.2013.00119.xCitations: 13AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Summary Primary delayed ejaculation (DE) is a relatively uncommon condition and has not been studied broadly. In this study, we aimed to investigate the clinical characteristics and penile afferent neuronal function using somatosensory evoked potentials in patients with primary DE. Twenty-four patients with primary DE and 24 age-matched normally potent men were enrolled in this study. Results indicated that patients with primary DE had remarkably higher frequency of masturbatory activity (especially, some with idiosyncratic styles), lower night emissions, longer intravaginal ejaculation latency time (IELT), higher anxiety and depression states (p = 0.010, p = 0.017, p < 0.001, p < 0.001, p < 0.001 respectively). In addition, the mean penile shaft sensory threshold values in the patients were considerably higher than those in the healthy men (p < 0.001). Mean latencies of dorsal nerve somatosensory evoked potential DNSEP were 4.32 ms longer in the DE group than those in the control group (p < 0.001). However, the latencies of glans penis somatosensory evoked potential (GPSEP) between the two group showed no significant difference (p = 0.985). At the same time, in comparison with the control group, the amplitudes of DNSEP were considerably lower in the DE group (p = 0.016), but not in the amplitudes of GPSEP (p = 0.934). This study indicates that the patients with primary DE appear to have penile shaft rather than glans hyposensitivity and hypoexcitability, and adaptation to a certain masturbatory technique (higher and idiosyncratic) may be related to the causes of primary DE, which is also associated with lower night emissions, longer IELT, higher anxiety and depression states. Introduction Delayed ejaculation (DE) is one of the diminished ejaculatory disorders, which are grouped as alterations of ejaculations (or orgasm), including various delays in ejaculatory latency (even completely unable to ejaculate), retrograde ejaculation and anejaculation, as well as decreases in seminal fluid volume, reductions in the force and sensation of ejaculation (Perelman et al., 2004). The DE disorder is relatively rare, with a prevalence ranging from 1 to 10% depending on age and comorbidities in adults, and is less studied (Perelman & Rowland, 2006). Based on the criteria established by the American Psychiatric Association (2000), DE is characterized as follows: (i) Men undergo persistent or recurrent delay in, or absence of, orgasm after a normal sexual excitement phase during sexual activity, which is judged to be adequate in focus, intensity and duration by the clinician, taking the person's age into account; (ii) The disturbance causes marked distress or interpersonal difficulty; (iii) It is not associated with another Axis I disorder or caused exclusively by the direct physiologic effects of a substance or general medical condition. The mechanisms related to the development of DE are largely unknown. Similar to premature ejaculation, DE could be distinguished as either acquired form, which occurs obviously somewhere in one's life after a period of normal sexual functioning, or primary one, which presents from early adulthood when a male reached sexual maturity (Rowland et al., 2010). Acquired DE is mainly because of medication factors, hypoandrogenism, spinal injuries (traumatic or iatrogenic) with lumbar sympathetic nervous system damaged, or neurodegenerative disorders, such as multiple sclerosis or diabetic neuropathies (Waldinger & Schweitzer, 2005). In addition, psychological and behavioural factors, including masturbatory habits, partner attraction, could also result in acquired DE (Althof, 2012). Based on the previous psychological view, primary DE is regarded as to be caused by social anxiety, fear, interpersonal hostility and relationship disorders (Shull & Sprenkle, 1980). Recently, some animal studies indicate that primary DE is a neurobiological variation in a 'normal' ejaculation statistical distribution curve, and it may be related to neurobiological disturbances, such as hypofunction of 5-HT1A receptor and/or hyperfunction of 5-HT2C receptor (Waldinger & Schweitzer, 2005). Somatosensory evoked potentials (SEPs) are widely used in investigating afferent neuronal function and more recently used to demonstrate changes in afferent neuronal function in patients with erectile dysfunction and premature ejaculation (Xin et al., 1997; Kaiser et al., 2001). Considering that SEPs yield information regarding conduction velocity and response amplitudes, we can apply it to estimate the function of the afferent pathways. In the current case–control study, we investigated the clinical characteristics of men with primary DE, and assessed the penile afferent neuronal function to investigate whether primary DE is allied to blunted penile perception, or the impairment of sensory function is secondary to an alteration in peripheral afferent neuronal function. Materials and methods Subjects We enrolled 24 consecutive patients with primary DE who attended the Andrology Department of our hospital, from September 2011 to March 2013. The primary DE was defined as previously described (Waldinger & Schweitzer, 2005). The criteria were: (i) be in a stable, heterosexual relationship with a fixed, non-pregnant sexual partner for at least 6 months; (ii) experience DE from their first sexual encounters; (iii) have possible sexual intercourse ≥1/week; (iv) undergo DE in every intravaginal sexual encounter; and (v) view their long latency as a problem and seek medical treatment for this condition. The patients were excluded if they had any of the following: (i) acquired DE; (ii) use of drugs that disrupt ejaculation, including tricyclic or serotoninergic antidepressants, antidopaminergics, α and β blockers, adrenergic neuron blockers, etc.; (iii) history of any significant psychiatric disorders; (iv) general medical condition such as diabetes mellitus, hypogonadism, hypertension, multiple sclerosis and peripheral neuropathy; (v) substance abuse (alcohol or drugs); (vi) history of pelvic surgery; and (vii) erectile dysfunction. Twenty-four age-matched controls were chosen from the husbands of women, who attended the Assisted Reproductive Center of our hospital for artificial insemination during the same period of time. The controls had regular sexual activity with the fixed, heterosexual partner for at least 6 months, and did not have erectile dysfunction, genitourinary tract infection, systemic (diabetes, alcoholism, hypertension, hyper- or hypo-thyroidism, etc.), neurological diseases, psychiatric disorders or substance abuse that might affect sexual activities. This study was carried out according to the Declaration of Helsinki and approved by the institutional review boards of Nanjing Drum Tower Hospital. All subjects signed an informed consent. All subjects underwent collection of general information and complete sexual history, physical examinations, intravaginal ejaculation latency time (IELT) during intercourse and self-administration International Index of Erectile Function-5 (IIEF-5) (Rhoden et al., 2002). Besides, all the participants completed the Beck Depression Inventory (Beck et al., 1961) and Zung Self-Rating Anxiety Scale (Zung, 1974). IELT was assessed with a clock during a 4-week period, during which participants were asked to have sexual intercourses at least four times. Methods An Electromyograph and Evoked Potential Equipment (Keypoint 4; Alpine BioMed ApS, Copenhagen, Denmark) was used to measure penile shaft sensory threshold and SEPs. Penile shaft sensory threshold was detected by electrical stimulation with a pair of ring electrodes. We placed the anode ring on the subcoronal region and fixed the cathode ring on the shaft 2 cm adjacent to the anode. The duration of stimuli was 1.0 ms and the frequency was three per second. Penile shaft sensory threshold value was determined by gradually increasing from 0 mA until the subject sensed tiny synchronous prickle stimulation. Subsequently, it was decreased step by step until the subject just could not feel the stimulation. The decreasing intensity was considered as the critical value. The same procedure was repeated three times and all the critical values were recorded and averaged to estimate the sensory threshold of penile shaft (Yilmaz et al., 1999; Zhou et al., 2010). Somatosensory evoked potentials consisted of DNSEP and GPSEP, with two different electrical stimulation places: (i) DNSEP: After the measurement of penile shaft sensory threshold, electrical stimuli were applied to the penile shaft via ring electrodes with an intensity of three times that of the threshold value at the same duration and frequency as described above. (ii) GPSEP: To examine whether there are differences in the cerebral response to the same intensity stimuli, we delivered electric power (10.0 mA) using a pair of round surface electrodes placed at the glans penis among all the subjects. Recording electrodes consisted of two needles. On the basis of the international 10–20 electrode placement protocol (Ernst & Fernando, 2004), we put the recording needle electrode in the scalp 2 cm behind the Cz electroencephalographic, fixed the reference needle electrode in the Fpz recording site and placed the grounding electrode on the right forearm. Responses were recorded on the skin with an impedance off <5 kΩ. We performed the SEP tests twice and each time averaged 200 cortical potentials. When the results of the two tests differed remarkably (when the latency varied more than 4.0 ms), the test was repeated three or four times to assess the test-to-test variability. The latencies and amplitudes of SEPs were recorded in the results. The latency was determined from the onset of the stimulus to the first positive peak cerebral response. The amplitude was measured peak-to-peak (between the positive peak and the following negative trough). Statistical analysis The Kolmogorov–Smirnov was applied to test the normal distribution. Continuous variables normally distributed were expressed as mean ± standard deviation and compared by independent t-test between two groups; quantitative data non-normally distributed were presented as median (interquartile range) and compared with non-parametric test. Chi-squared test or Fisher's exact test was used for categorical variables. In addition, Pearson correlation was estimated for two variables. All statistical analysis was performed with spss V16.0 (SPSS Inc., Chicago, IL, USA). A two-sided p < 0.05 was considered statistically significant. Results The clinical characteristics of the patient and control groups are shown in Table 1. The duration of DE symptoms for the patients ranged from 0.5 to 16 years (median 3 years). According to Kaplan classification (Abdel-Hamid & Saleh, 2011), severity of DE was classified into four categories: (i) anejaculation; (ii) ejaculation and orgasm with automanipulation in the absence of the sexual partner; (iii) ejaculation and climax with automanipulation in the presence of the partner but not during copulation; and (iv) ejaculation and orgasm are still likely, but only after prolonging intercourse and making great effort. In this study, the number of the above DE syndromes among the patients was 2 (8.3%), 10 (41.7%), 4 (16.7%) and 8 (33.3%) respectively. Of the 22 patients who had a history of masturbation, two patients (9.1%) could not ejaculate in spite of masturbation, and five (22.7%) ejaculated only with idiosyncratic masturbation (three patients reported masturbation with their penis rubbing against the bed sheets, one patient showed masturbation with pressure on the perineum when reading erotic books and one patient masturbated by urethral instrumentation), the others (68.2%) could regularly reach ejaculation during masturbation, stroking their penis manually in the usual pattern. Eleven (45.8%) patients felt that masturbation was more enjoyable than intercourse. All the patients had normal erectile function as examined by IIEF-5. Except for intermittent nocturnal emissions, there was no statistically significant difference in marital status, age, height, body weight and level of education between the two groups. However, compared with those in the controls, the scores of the anxiety and depression were higher in the patients. Table 1. Comparisons between patients with primary delayed ejaculation and controls Characteristics Patients (n = 24) Controls (n = 24) p Age (years) 29.5 ± 4.8 30.6 ± 6.6 0.503 Weight (kg) 72.3 ± 12.8 73.5 ± 9.8 0.702 Height (cm) 172.3 ± 6.5 173.2 ± 4.6 0.588 Marital status, n (%) Married 21 (87.5) 23 (95.8) 0.609 Single 3 (12.5) 1 (4.2) Level of education, n (%) Graduate 8 (33.3) 7 (29.2) 0.283 High school 9 (37.5) 5 (20.8) None or primary school 7 (29.2) 12 (50.0) History of masturbation, n (%) Frequently (≥2 times/week) 16 (66.7) 4 (16.7) 0.010 Infrequently (≤1 time/week) 6 (25.0) 12 (50.0) Never 2 (8.3) 8 (33.3) Intermittent nocturnal emissions, n 11 19 0.017 Beck Depression Inventory (scores) 16.1 ± 4.0 10.1 ± 3.1 <0.001 Self-Rating Anxiety Scale (scores) 40.0 ± 8.1 27.7 ± 4.2 <0.001 IELT (min) 20.0 (15.0–24.5)a 5.5 (4.0–7.5) <0.001 IIEF-5 23.5 ± 1.1 23.9 ± 0.9 0.257 IELT: intravaginal ejaculation latency time; IIEF-5: International Index of Erectile Function-5. a Two patients could not ejaculate. Their IELTs were calculated from the start of vaginal intromission to the cease of sexual activity due to exhaustion. The mean penile shaft sensory threshold values in the control and DE group were 1.83 ± 0.44 and 2.46 ± 0.69 mA respectively (p < 0.001, Fig. 1A). The SEP (DNSEP and GPSEP) waveforms were obtainable as M-shaped (shaped in the form of the letter M) in all the subjects, and Fig. 2 shows the typical waveforms of DNSEP in the patient and healthy men. The mean latencies of DNSEP and GPSEP were 42.58 ± 1.95 and 44.71 ± 1.73 ms in the healthy group, respectively, and 46.90 ± 4.76 and 44.69 ± 2.75 ms in the DE group respectively. The mean latencies of DNSEP were 4.32 ms longer in the DE group than those in the control group (p < 0.001, Fig. 1B), but the mean latencies of GPSEP in the two groups had no significant difference (p = 0.985). In respect of the possible differences in DNSEP and GPSEP nerve conduction pathways (Xin et al., 1997), we also compared the latencies of DNSGP and GPSEP. The mean latency of DNSEP was shorter than that of GPSEP in the healthy group (p < 0.001, Fig. 1B), whereas the mean latency in the dorsal nerve was 2.20 ms longer than that in glans in the DE group (p = 0.080). Figure 1Open in figure viewerPowerPoint (A) Mean sensory thresholds of the penile shaft. (B) Mean latencies of dorsal nerve somatosensory evoked potential (DNSEP) and glans penis somatosensory evoked potential (GPSEP). #p < 0.001 for patients with primary delayed ejaculation versus normal subjects. *p < 0.001 for DNSEP versus GPSEP in the normal subjects. Figure 2Open in figure viewerPowerPoint Results of somatosensory evoked potential of dorsal nerve (DNSEP). DNSEP recording of (A) the normal potent man and (B) the patient with primary delayed ejaculation. The Kolmogorov–Smirnov test indicated that the amplitudes of both DNSEP and GPSEP were non-normally distributed. The amplitudes of DNSEP and GPSEP in the control subjects were 1.32 (1.09–1.74) and 1.59 (1.30–2.13) μV, respectively, and those in the DE patients were 0.93 (0.70–1.42) and 1.57 (1.24–2.10) μV respectively. The amplitudes of DNSEP were significantly lower in the DE group than those in the control group (p = 0.016), however, no remarkable difference was found in the amplitudes of GPSEP (p = 0.934). The amplitudes of GPSEP were statistically larger than those of DNSEP in both the groups (p = 0.040 and p < 0.001 respectively). In the patient group, there was a positive correlation between the penile shaft sensory threshold and the latencies of DNSEP (r = 0.427, p = 0.037), but not in those of GPSEP (p = 0.731). In addition, latencies of DNSEP and masturbatory history also had a good correlation (r = 0.469, p = 0.021). However, no correlation was observed between latencies of DNSEP and anxiety or depression scores (p = 0.251 and 0.457 respectively). Discussion A large number of diagnoses have been crafted to describe DE over the past years. However, there have been no evidence-based or specific operational criteria on how to accurately diagnose a man with DE. Based on the fact that most sexually functional men's IELT is about 4–10 min (Patrick et al., 2005), a clinician might consider that a man meets DE if his IELT is beyond 25 min, which is greater than or equal to the mean plus 2 standard deviations (Althof, 2012). However, in addition to IELT, the patients also have evidence of distress or simply cease intercourse because of exhaustion or pain for this diagnosis (Althof, 2012). Our results showed that median IELT of the patients was 20 min, but the anxiety and depression scores were higher than those of the healthy men, which is in agreement with the reports of previous studies (Corona et al., 2010; Abdel-Hamid & Saleh, 2011). Ejaculation is a reflex action controlled by the central nervous system via mediating the spinal ejaculation generator, and it is typically divided into two distinct successive phases: emission and expulsion (Giuliano, 2011). Somatosensory inputs from the genital area converge to the spinal cord through two main pathways (Giuliano, 2011): one afferent pathway is the dorsal nerve of the penis (DNP), the other one is the fibres, which travel along the hypogastric nerve and enter the spinal cord via thoracolumbar dorsal roots. The most numerous afferent terminations of sensory receptors in the male genital pathway are free nerve endings (FNE) of thin myelinated Aγ (Halata & Munger, 1986). FNE receptors can perceive mechanical (stretch, vibration, touch, pressure) stimuli, as well as temperature and pain, translating multiple sensory inputs to excitory signals (Halata & Munger, 1986). Allard et al. (2005) proposed that a certain number of peripheral stimulation is required to trigger ejaculation, depending on not only the descending input from supraspinal centres but also the intrinsic capacitance of the spinal ejaculation generator. Alternatively, both experimental and clinical data have showed that inputs conveyed by DNP are necessary for ejaculation (Pescatori et al., 1993; Wieder et al., 2000). In the anaesthetized and spinalized rats, ejaculation reflexes could be elicited by electrical stimulation of the DNP (Pescatori et al., 1993). Similarly in patients with spinal cord injury, ejaculation induced by vibratory stimulation of the glans could be inhibited through local anaesthesia of the DNP (Wieder et al., 2000). A limited number of studies have focused on the mechanisms of primary DE. One reason may be that it is a relatively uncommon condition. On the other hand, clinicians erroneously perceive that DE could allow a man to have sufficient time to bestow multiple coital orgasms to his partner. However, DE causes significant sexual dissatisfaction, relationship distress, as well as anxiety regarding men's sexual performance and general health issues (Althof, 2012). Our results indicated that DE patients were associated with increased depression and anxiety scores, which further supports the negative effects of DE on the quality of life. To the best of our knowledge, the SEPs have not been previously applied in DE patients. DNSEP is an electroencephalographic response after stimulating the somatic sensory area, which is innervated by the penile dorsal nerve, whereas GPSEP is a modification in DNSEP by sending stimuli at the glans penis. They provide objective neurophysiologic data for the complete peripheral and central nerve afferent pathway (Xin et al., 1995). The Kolmogorov–Smirnov test indicated that the latencies of SEPs were normally distributed, but the amplitudes were not. This may be related to the fact that the amplitudes of various evoked potential components, which vary greatly by individual, are affected by stimulation, recording parameters and biological factors, and the amplitudes are considered to be much less important than latency measurement in diagnostic value (Nikiforidis et al., 1995). Our results showed that the mean penile shaft sensory threshold values were remarkably increased in the DE patients; in addition, the latencies and amplitudes of DNSEP were considerably longer and lower, whereas the latencies and amplitudes of GPSEP had no differences between the two groups. These results imply that the sensation in the nerves of the penile shaft, rather than glans penis, is reduced in the patients. This may be in part a consequence of high frequent masturbation, under which condition the penile shaft (not glans penis) was stimulated manually for a long time, reducing the penile shaft local skin sensory sensitivity. In addition, the nerve fibres innervating the glans penis are with a predominance of FNE, abundant genital end bulbs and scarce Pacinian and Ruffinian corpuscles, which are different from those innervating the penile shaft (Halata & Spaethe, 1997). Besides, it is suggested that the glans is innervated not only by DNP but also other sensory fibres, such as the perineal nerve (Yang & Bradley, 1999). Based on the above differences, we could explain why there are changes only in DNSEP, but not in GPSEP, in the patients. It is well known that prolonging sensory latency and decreasing penile hyperexcitability have been used to treat premature ejaculation with local anaesthetics (Xin et al., 1995; Pu et al., 2013). Thus, we consider that the increased DNSEP latencies may result from any of the following: receptor dysfunction, reduced activation of afferent nerves and slowed peripheral neuronal conduction. However, this hypothesis needs to be confirmed by histopathologic and functional studies. As with many biobehavioural responses, ejaculation behaviour is undoubtedly controlled by both biological and psychological–behavioural factors. Perelman & Rowland (2006) pointed out that the variable ejaculatory latency in each individual may be biologically established, however, the actual time to reach ejaculation within the range depends on a variety of variables, such as sexual context, psychological–behavioural state and partner relationship. Our current study displayed that only 9% of DE patients did not or could not masturbate to ejaculate, whereas 91% patients were capable of masturbation to ejaculate. It is likely that ejaculatory latency in the patients is usually quite different during coitus from during masturbation (Rowland et al., 2000), which further supports the viewpoints of Perelman & Rowland (2006). In addition, 66.7% patients carried out high frequency masturbation and 22.7% patients involved an idiosyncratic masturbation. Particularly, in our study, 45.8% DE patients presented that they enjoyed more from masturbation than from intercourse. These results are consistent with the findings of Perelman (2005). The pressure, speed, duration and intensity of masturbation are idiosyncratic and different from what the men experienced during intercourse; therefore, the men who frequently engage in self-stimulation make difficulties in ejaculating with a partner, leading to the occurrence of DE. In addition, the reality of sex with the partner and the use of sexual fantasy (whether affected by the erotic stimulation unconventionally or not) during masturbation is discrepant in body type, orientation and sex activity performed from, and this disparity may be another potential cause of DE (Rowland et al., 2010). Until now, clinicians have no good solutions to treat primary DE. Our results support Perelman's perspective on DE treatment: the patients should temporarily suspend masturbatory activity, at least reducing the frequency, and limit orgasmic release to their desired goal activity, for example, orgasm during penetrative sexual encounters with their partner. In addition, patients should use fantasy and bodily movements during intercourse, which make the thoughts and sensation intensity comparable to the experienced conditions in masturbation (Perelman, 2013). There are some limitations and deficiencies within this study. The electrical stimuli used in the study were not physiological. Electrical stimulation results in non-specific activation of the nerve fibres, which supply to the penis. However, the electrical stimulation has the advantage of rapid on/off, thus producing better quality evoked potentials than that of mechanical stimulation. Another limitation is the patients' number was relatively small. Thus, further studies with more primary DE patients are warranted to confirm the findings in the present investigation. Conclusions Patients with primary DE appear to have penile shaft rather than glans hyposensitivity and hypoexcitability. Adaptation to a certain masturbatory technique (higher and idiosyncratic) may be a cause of primary DE, which is also associated with lower night emissions, longer IELT, higher anxiety and depression states. Acknowledgements The study was supported by the National Natural Science Foundation of China (nos. 81170563 and 81270694). 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