A conservative therapy is frequently advocated in the acute phase of PD to relieve the penile pain or prevent the progression of penile curvature, but the evidence on the topic is still limited. PDE5Is are part of the conservative management of patients with PD, however, they are traditionally used to improve erection in this population [23]. In recent years, preliminary evidence, first in animal models and in vitro and subsequently in humans, have highlighted the antifibrotic and analgesic potential of long-term administration of PDE5Is in PD [15, 24, 25].
Clinical evidence on PDE5Is in PD patients
A recent survey of 401 sexual medicine experts across Europe found that the most common oral medication prescribed for the treatment of PD was Tadalafil 5 mg once daily (57.4%) [16]. Palmieri et al. showed in a randomized controlled trial (RCT) on PD patients complaining of ED that ESWT plus Tadalafil 5 mg once daily significantly improved IIEF-5 and quality of life (QoL) compared to ESWT alone at 6 months [3]. Dell’Atti compared intralesional verapamil injection (IVI), Tadalafil 5 mg daily, and IVI plus Tadalafil 5 mg daily in a 3-month RCT on PD patients. Penile pain resolved completely or partially in 57%, 61%, and 76% of cases, respectively. A slight reduction in penile curvature was recorded in all groups with no significant differences compared to baseline. Plaque size remained stable in IVI alone and Tadalafil alone groups, significantly decreasing in the combination group. IIEF-5 significantly improved in Tadalafil alone and combination groups, with a statistically significant difference in favor of the latter [26]. Hatampour et al. compared intraplaque injection of dexamethasone plus Tadalafil 5 mg once daily and IVI in another 3-month RCT on chordee patients with PD. Degree of penile curvature, plaque count, and plaque size decreased significantly in both groups from baseline, with no significant difference between the groups [27]. Chung et al. evaluated PD patients with septal scars undergoing Tadalafil 2.5 mg daily over a 6-month period in a retrospective controlled study. The Tadalafil group reported a significantly higher IIEF-5 score and significantly more frequent septal scar resolution than the control group. Besides, 5 patients in the control group and only 1 subject in the Tadalafil group showed worsening or penile curvature during the follow-up [14]. Ozturk et al. compared Sildenafil 50 mg daily and Vitamin E 400 IU daily in a RCT with 3 months of follow-up. IIEF-5, penile curvature, plaque volume, and pain score were significantly improved from baseline in the Sildenafil group. Moreover, the improvements in IIEF-5 score and pain score were statistically significant in Sildenafil group compared with Vitamin E group [15].
Molecular mechanisms of PDE5Is in PD
Several studies on fibrosing diseases (e.g., idiopathic pulmonary fibrosis, Duchenne muscular dystrophy, cardiac and renal fibrosis) showed that PDE5Is have antifibrotic properties [28]. Growing evidence is showing that continuous therapy with PDE5Is may block or reverse fibrosis of the corpora cavernosa and tunica albuginea, with antifibrotic mechanisms independent of the well-known effect of vasodilation and increased blood flow associated with these drugs. Continuous PDE5Is administration induces a sustained elevation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in the penile tissues. This pathway, probably by activating protein kinase G (PKG), leads to decrease profibrotic factor secretion (e.g., TGF-β1), myofibroblasts count, and collagen deposition [13]. Myofibroblasts are “the most intensive collagen factory”. Oxidative stress and inflammation typical of the acute phase of PD promote local fibroblast-to-myofibroblast conversion. Sustained levels of NO and cGMP seems hinder this differentiation and promote myofibroblast apoptosis. The timing for the administration of PDE5Is could be essential, a recent study suggests that these drugs can prevent but not reverse myofibroblast transformation, therefore, they should only be used in the early stage of PD for antifibrotic purposes [29]. However, the antifibrotic mechanisms of PDE5Is in the penile tissues are probably still largely unknown and some of them could be partially or totally independent from the NO/cGMP pathway. Finally, we hypothesize that an anti-inflammatory and antioxidant effect of continuous PDE5Is may contribute to the reduction of penile pain in patients with PD, however this statement is not currently supported by solid biomolecular evidence [24, 25, 30].
Our main findings
In this study we compared the clinical outcomes of PD patients receiving Tadalafil 5 mg daily or observation. Interestingly, we found that the penile curvature progression rate was significantly lower in patients taking Tadalafil than men under observation (p = 0.042). This finding supports the hypothesis that PDE5Is may interfere with the pathogenesis of fibrosis in PD patients [31]. Moreover, the difference between the two groups was significant (p = 0.002) only when considering patients with short duration of the disease (≤ 9 months). This result suggests a substantial benefit especially when therapy with PDE5Is is started early.
Furthermore, in patients receiving Tadalafil we observed a predictable significant improvement in the IIEF-5 score and statistically significant higher scores compared to subjects in the observation group. This finding aligns with the recommendation of the EAU guidelines to offer PDE5Is to PD patients to improve erection and optimize penetration [9].
Finally, we found a significant improvement in the PDQ-Overall and PDQ-PP scores of men treated with Tadalafil and stable scores in observed patients. Consequently, despite a statistically significant difference at baseline in favor of the observation group, no statistically significant differences were recorded between the two groups at 12 weeks. This result supports previous evidence on the analgesic effect of PDE5Is in PD patients [15].
Strengths and Limitations
To the best of our knowledge this is the first study specifically designed to evaluate the clinical outcomes of patients in acute phase of PD treated with Tadalafil 5 mg daily alone. Furthermore, despite the relatively small sample size, this is to date the clinical study on the topic with the largest cohort of patients evaluated. Other significant strengths of this paper are the well-defined methodology, the presence of a comparative group, and the use of validated tools for measuring outcomes. However, our research should be read and interpreted considering various issues. The main limitation is the retrospective design. Another weakness, caused by the lack of randomization, is the presence of some significant differences at baseline between the intervention and observation group. There is no univocal definition of penile curvature progression, therefore it was decided arbitrarily, this may have influenced the direction of the results. The course of PD is unpredictable and especially for patients with time from onset > 9 months the improvement in clinical outcomes could be due in part to spontaneous disease stabilization rather than PDE5Is [31]. Only men with penile pain and progressive worsening of the penile curvature were included in the study, but it is known that a significant proportion of subjects in the acute phase of PD may have no pain or progression of the curvature [32]. In addition, the selected patients had overall a mild penile curvature and all complained of ED. Finally, only men who had not discontinued Tadalafil treatment were included, although it is known that not negligible percentage of patients treated with PDE5Is may discontinue therapy for various reasons [22, 33]. These last three issues could hinder the generalizability of our results. Noteworthy is that a relevant number of men included had calcified plaques, suggesting that, despite the symptoms, some subjects were closer to stabilizing the disease. However, the concept of calcified plaque as a pathognomonic sign of stable disease is currently under discussion and there was no significant difference between the intervention and observation groups regarding the presence of calcified plaques [34].