Second level diagnostic evaluation uses specialistic instrumental exams that can be helpful for accurate aetiological diagnosis of ED.
Penile dynamic colour-duplex Doppler ultrasonography allows direct visualization of penile vessels and evaluation of possible strictures and dysfunctions. Using Doppler methodology urologists are able to study both arterial and venous flow velocity, assessing erectile haemodynamics as a whole. This exam is performed after injection of alprostadil (PGE 1 ) 10 or 20 mg in order to induce erection and reduce false positive; some authors reported that oral administration of sildenafil seems to be as effective than PGE1 in inducing erection, but less invasive and more capable of reducing false positive venous leakage diagnosis. If full rigidity is not obtained after a period of privacy and self-stimulation, a second injection (alprostadil 10 mg plus phentolamine 1-2 mg) should be performed in order to achieve the best erection and get over anxiety-induced failures.
Ultrasonoghrapy is performed 5-10 minutes after injection, using high-frequency linear transducers (7.5-13 MHz). When it’s possible, Power Doppler technique should be used because of better definition of vascular details and less dependence on transducer position.
During exam, parameters which could be mainly considered are the Peak Systolic Velocity (PSV), the End Diastolic Velocity (EDV) and the Resistance Index (RI= (PSV-EDV)/PSV); the last one can predict venous leak probability in patients suffering ED.
Dynamic ultrasonography also allows to value anatomical aspects of penile circulation (for example strictures, high-speed jets, duplication of the cavernosal artery, cross-communications between the two cavernosal arteries, etc.) and corpora cavernosa, especially after vasoactive drugs injection.
Men with normal erectile function present a PSV value > 30 cm/s and an EDV value< 5 cm/s and the RI always >
0.85. As the PSV decreases with ageing, the PSV cut-off value should be calculated as following in order to increase test predictivity: PSV = 6.73 + (0.7 * age).
Patients showing normal PSV value and complete erectile response can be considered as normal subjects; patients showing low PSV value but normal erection probably suffer arterial insufficiency, offset by effective veno-occlusive system (RI > 0.85).
In patients showing normal PSV value associated with incomplete erectile response and RI value under 0.85, a probable veno-occlusive mechanism alteration should be considered as cause of erectile dysfunction. Nevertheless, penile dynamic colour-duplex Doppler ultrasonography is not sufficient to make diagnosis of venous leak because of its low specificity due to incomplete rigidity of corpora cavernosa and persistence of diastolic flow. In order to formulate a correct diagnosis of venous leak gold standard remain the cavernosometry/cavernosography.
Role of penile Doppler ultrasonography has been discussed because it provides operator dependent information and, considering currently available therapy for ED (especially PDE5-inhibitors), rarely alters following patient management.
Some evidences open new diagnostic possibilities for penile dynamic colour-duplex Doppler ultrasonography. A statistically significant correlation between PSV decrease and ischemic heart disease was found, probably due to a greater sensibility of penile vessels towards atherosclerosis promoting factors.
Thus ultrasonography could become a non-invasive screening test in order to value coronary risk. Moreover penile dynamic colour-duplex Doppler ultrasonography conserves a very important role in investigating patients refractory to PDE5-inhibitors therapy (especially in detecting arterio-venogenic disorders).
If suspect of veno-occlusive dysfunction arises during penile dynamic, next diagnostic level is represented by cavernosometry/cavernosography. However, there is no gold standard in literature on whether to perform cavernosometry alone or with cavernosography, which flow values (induction or maintenance) should be measured, which drug should be used, whether a standard cavernous pressure of rigidity exists or does it change from case to case and whether the examination can indicate an effective therapeutic choice. Even if cavernosometry is a reliable test in the evaluation of patients with vascular erectile dysfunction, it should not be used alone to decide treatment. In these cases the therapeutic management is difficult, since the alternatives (high pharmacological doses, drug combinations, venous surgery, prosthesis implants) are serious for the patients. Cavernosometry could be useful to select patients for surgical therapy and during follow-up of patients not responding to venous surgery alone or with pharmacotherapy.
Among second level test it is included also NPTR (RigiScan), which offers an objective and quantitative evaluation of nocturnal erections. Nocturnal penile erections physiologically occur 3-5 times during sleep, usually in conjunction with R.E.M. phase.
When this test is performed in men without sleep disorders which can alter NPTR, it allows to distinguish between organic and psychogenic ED in the majority of patients.
RigiScan is performed by applying two elastic rings placed at the basis and the tip of the penis connected to RigiScan recorder placed on one leg. Nocturnal erections must be recorded at least for two consecutive nights. RigiScan criteria for ED are the following: less than 60% of tip and base rigidity, less than 2 cm increase of tip tumescence, less than 3 cm increase of base tumescence, less than three full erections during night and less than 10 min of full erection during night. Patients suffering organic ED present at three of these criteria, while patients suffering psychogenic ED have normal erections.
Although many studies confirmed that NPRT is the best non-invasive diagnostic test for differentiating psychogenic from organic dysfunction, others claimed that NPRT effectiveness is limited by anxiety and sleep disorders. Moreover, NPTR parameters are closely related to androgen levels and advanced age. Additionally, there are no standard evaluation criteria of NPTR and different studies have adopted different criteria.
As showed in many clinical trials, RigiScan sensibility in distinguishing between organic and psychogenic ED varies from 82 to 98%. In order to obtain a certain etiological diagnosis of ED, other test (penile dynamic colour-duplex Doppler ultrasonography, cavernosometry) are needed, because NPRT can differentiate psychogenic from organic ED, but it is not able to identify causes of organic dysfunction (arterial, venous, neurogenic).
Rarely specific neurological alterations involving both central and peripheral nervous system can determinate ED. If urologist suspects a neurological aetiology, he can perform specific tests investigating penile and genital conduction effectiveness. These tests include biothesiometry, speed of conduction of the dorsal penile nerve, bulbocavernous reflex, somatosensorial evoked potential and perineal electromyography. In most cases, careful anamnesis and neurological physical exam allow to detect neurological condition underlying ED, limiting the use of more specific diagnostic tools to selected patients.
Via Pansini 5, Napoli, Italy
Via Pansini 5, Napoli