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Editorial: Erectile Dysfunction
0022-5347/95/15351494$03.00/0
Vol. 153, 1494-1495, May 1995 Printed in V.S.A.
k JOURNAL OF UROLOGY Copyright 0 1995 by ADaERlCAN UROIIDGICALASSOCIATION, INC.
EDITORIAL: ERECTILE DYSFUNCTION M e r e n t somatic neuro-integrity is critical for normal erectile function in animals and humans. The penis is well represented in the cortical sensory homunculus. However, a paucity of sensory nerve endings exists in the penis, particularly in the glans penis. Although the glans penis contains only primitive nerve endings, the epidermis of the penile shaft is similar to that found elsewhere and contains more complex mechanoreceptors, including pacinian corpuscles. Therefore, vibratory stimuli must be applied to this portion of the penis. Penile afferent neurological testing is performed most accurately by complex neurophysiological studies, particularly genito-cerebral evoked potential testing. These studies are able to localize (peripheral and central), lateralize and characterize the specific neuropathology. However, they are expensive and time-consuming, and require a trained technician and a cooperative patient. Sensory deficit erectile dysfunction is a syndrome that occurs in the presence of neuropathology in the somatic afferent pathway. It is seen with aging and in the presence of polysensory peripheral neuropathy, particularly that associated with diabetes mellitus and alcohol toxicity. However, it is not common as an occult isolated entity and, therefore, routine neurophysiological testing is not cost-effective. We proposed that simple quantitative vibratory testing by penile biothesiometry serve as a routine cost-effective screening study to select more effectively patients for more sophisticated neurophysiological testing and neurological consultation.' Bemelmans et a1 (page 1483) found a poor correlation between these 2 studies. However, they examined only the glans penis by vibratory testing. Additionally, they found no correlation between patient age and the vibratory threshold of the glans penis. Rowland et a1 (reference 18 in article) compared vibro-tactile and electrical stimulation thresholds in healthy young men, older men and impotent diabetic men. The vibrotactile stimulus in this study was applied to the shaR of the penis 10 mm. from the coronal ridge. These investigators, in contrast, found a positive correlation between vibro-tactile and electrical stimulation thresholds in these groups, and both were positively correlated with patient age. This age dependency is explained by pacinian degeneration, collagen infiltration and dermal atrophy. A study group of 118 normal potent men were, therefore, used to develop an age stratified nomogram of normal values (see table).' Additionally, in another study 137 impotent men underwent biothesiometric testing as well as genito-cerebral evoked potential studies. Of the 38 patients with a normal biothesiometric examination 80% had a normal evoked potential study, which increased to 93% among patients less than 60 years
Age adjustment for penile biothesiometry No.
Pt.
Shaft
Finger
Glans
Age
Pts'
Range
Rt.
Lt.
Rt.
Lt
18 22 31 31 10 9
17-29 30-39 4 M 9 5039 60-69 70-75
5 5 5 6 6 7
5 5 5 6 6 7
5 6 6 8 9 14
5 6 6 8 9 14
6 7 7 9 10 16
old. Of the 99 patients with a n abnormal biothesiometric examination 47% had an abnormal evoked potential result. Therefore, biothesiometry of the penile shaft is a simple and cost-effective screening tool for sensory deficit erectile dysfunction. The description of nitric oxide as the critical nonadrenergic, noncholinergic neurotransmitter in the regulation of corporeal smooth muscle resulted in a clinical interest in nitric oxide donors as possible superior pharmacological agents for intracavernous administration. Martinez-Pifieiro et a1 (page 1487) compared the relative efficacy of the nitric oxide donor sodium nitroprusside and prostaglandin E l , and demonstrated the superior efficacy of prostaglandin E l . These investigators were also able to avoid the severe hypotension that Brock et a1 experienced with nitroprusside, which caused them to conclude that it is a n inappropriate treatment for impotence (reference 18 in article). Similar results were obtained by Porst when another nitric oxide donor, linsidomine chlorhydrate, was compared to prostaglandin E1.2 It should also be remembered that nitric oxide donors release superoxide radicals and, therefore, may act as mutagens. In contrast, alprostadil, the synthetic version of prostaglandin E l , is a safe and effective pharmacological agent for intracavernous administration that will most likely be the first drug to obtain Food and Drug Administration approval for this indication. As a single agent it is associated with a 75% response rate and when combined with phentolamine mesylate, as routinely done at our institution, it is associated with an 85% response rate. It appears to be an ideal pharmacological agent. Additionally, a noninjectable formulation of alprostadil has been developed that can be delivered effectively to the corpora cavernosa by intraurethral administration.3 Erectile dysfunction following transurethral resection of the prostate has been reported to occur in 5 to 40% of patients. Most studies to date have determined this incidence by questionnaire with or without nocturnal penile tumescence recording. Tscholl et a1 (page 1491) report, in a large series of patients, an organic impotence rate of 8.3% following transurethral resection of the prostate as determined by Snap-Gauge* testing. This, in fact, may be a n underestimation due to the lack of sensitivity inherent to nocturnal penile tumescence recording by Snap-Gauge as opposed t o the Rigiscan.* These investigators report a direct correlation between impotence after transurethral resection of the prostate and patient age, and an indirect correlation between it and the size of the adenoma resected. The latter finding is unique and underscores the need for informed consent in younger patients with small adenomas. Additionally, it further supports the need to implement aggressively alternative medical and interventional therapies in these patients before choosing transurethral resection of the prostate. The exact etiology of the organic erectile dysfunction resulting in impotence after transurethral resection of the prostate appears to be related to the initiation or worsening of preexisting corporeal veno-occlusive dysfunction.4 The corporeal veno-occlusive dysfunction may result from direct thermoelectric or coagulative electrocautery injury to the erectile tissue, a similar injury to the cavernous nerves that lie ad-
Upper limit [mean + 3 standard devlations) of normal values for perception thresholds in a population of potent men
1494
* Dacomed, Minneapolis,
Minnesota.
1495
ERECTILE DYSFUNCTION jacent to t h e prostatic capsule, or extravasation of irrigating fluid and t h e subsequent inflammatory reaction producing nerve or corporeal tissue injury.4 These pathogenic mechanisms may be more likely to occur during resection of a small gland.
Harin Padma-Nathan Department of Urology University of Southern California Medical Center Los Angeles, California
REFERENCES
1. Padma-Nathan, H.: Neurologic evaluation of erectile dysfunction. Urol. Clin. N. h e r . , 1 6 77, 1988. 2. Porst, H.: Prostaglandin E l and the nitric oxide donor linsidomine for erectile failure: a diagnostic comparative study of 40 patients. J. Urol., part 2, 149 1280, 1993. 3. Padma-Nathan, H., Keller, T., Poppiti, R., Lue, T., Tam, P. and Place, V.: Hemodynamic effects of intraurethral alprostadil the medicated urethral system for erection (MUSE).J. Urol., part 2,161: 345A, abstract 469, 1994. 4. Padma-Nathan, H., and Goldstein, I.: The pathogenisis of postl " impotence. J. Urol., part 2,139 2754 abstract 449,1988.
Vol. 153, 1494-1495, May 1995 Printed in V.S.A.
k JOURNAL OF UROLOGY Copyright 0 1995 by ADaERlCAN UROIIDGICALASSOCIATION, INC.
EDITORIAL: ERECTILE DYSFUNCTION M e r e n t somatic neuro-integrity is critical for normal erectile function in animals and humans. The penis is well represented in the cortical sensory homunculus. However, a paucity of sensory nerve endings exists in the penis, particularly in the glans penis. Although the glans penis contains only primitive nerve endings, the epidermis of the penile shaft is similar to that found elsewhere and contains more complex mechanoreceptors, including pacinian corpuscles. Therefore, vibratory stimuli must be applied to this portion of the penis. Penile afferent neurological testing is performed most accurately by complex neurophysiological studies, particularly genito-cerebral evoked potential testing. These studies are able to localize (peripheral and central), lateralize and characterize the specific neuropathology. However, they are expensive and time-consuming, and require a trained technician and a cooperative patient. Sensory deficit erectile dysfunction is a syndrome that occurs in the presence of neuropathology in the somatic afferent pathway. It is seen with aging and in the presence of polysensory peripheral neuropathy, particularly that associated with diabetes mellitus and alcohol toxicity. However, it is not common as an occult isolated entity and, therefore, routine neurophysiological testing is not cost-effective. We proposed that simple quantitative vibratory testing by penile biothesiometry serve as a routine cost-effective screening study to select more effectively patients for more sophisticated neurophysiological testing and neurological consultation.' Bemelmans et a1 (page 1483) found a poor correlation between these 2 studies. However, they examined only the glans penis by vibratory testing. Additionally, they found no correlation between patient age and the vibratory threshold of the glans penis. Rowland et a1 (reference 18 in article) compared vibro-tactile and electrical stimulation thresholds in healthy young men, older men and impotent diabetic men. The vibrotactile stimulus in this study was applied to the shaR of the penis 10 mm. from the coronal ridge. These investigators, in contrast, found a positive correlation between vibro-tactile and electrical stimulation thresholds in these groups, and both were positively correlated with patient age. This age dependency is explained by pacinian degeneration, collagen infiltration and dermal atrophy. A study group of 118 normal potent men were, therefore, used to develop an age stratified nomogram of normal values (see table).' Additionally, in another study 137 impotent men underwent biothesiometric testing as well as genito-cerebral evoked potential studies. Of the 38 patients with a normal biothesiometric examination 80% had a normal evoked potential study, which increased to 93% among patients less than 60 years
Age adjustment for penile biothesiometry No.
Pt.
Shaft
Finger
Glans
Age
Pts'
Range
Rt.
Lt.
Rt.
Lt
18 22 31 31 10 9
17-29 30-39 4 M 9 5039 60-69 70-75
5 5 5 6 6 7
5 5 5 6 6 7
5 6 6 8 9 14
5 6 6 8 9 14
6 7 7 9 10 16
old. Of the 99 patients with a n abnormal biothesiometric examination 47% had an abnormal evoked potential result. Therefore, biothesiometry of the penile shaft is a simple and cost-effective screening tool for sensory deficit erectile dysfunction. The description of nitric oxide as the critical nonadrenergic, noncholinergic neurotransmitter in the regulation of corporeal smooth muscle resulted in a clinical interest in nitric oxide donors as possible superior pharmacological agents for intracavernous administration. Martinez-Pifieiro et a1 (page 1487) compared the relative efficacy of the nitric oxide donor sodium nitroprusside and prostaglandin E l , and demonstrated the superior efficacy of prostaglandin E l . These investigators were also able to avoid the severe hypotension that Brock et a1 experienced with nitroprusside, which caused them to conclude that it is a n inappropriate treatment for impotence (reference 18 in article). Similar results were obtained by Porst when another nitric oxide donor, linsidomine chlorhydrate, was compared to prostaglandin E1.2 It should also be remembered that nitric oxide donors release superoxide radicals and, therefore, may act as mutagens. In contrast, alprostadil, the synthetic version of prostaglandin E l , is a safe and effective pharmacological agent for intracavernous administration that will most likely be the first drug to obtain Food and Drug Administration approval for this indication. As a single agent it is associated with a 75% response rate and when combined with phentolamine mesylate, as routinely done at our institution, it is associated with an 85% response rate. It appears to be an ideal pharmacological agent. Additionally, a noninjectable formulation of alprostadil has been developed that can be delivered effectively to the corpora cavernosa by intraurethral administration.3 Erectile dysfunction following transurethral resection of the prostate has been reported to occur in 5 to 40% of patients. Most studies to date have determined this incidence by questionnaire with or without nocturnal penile tumescence recording. Tscholl et a1 (page 1491) report, in a large series of patients, an organic impotence rate of 8.3% following transurethral resection of the prostate as determined by Snap-Gauge* testing. This, in fact, may be a n underestimation due to the lack of sensitivity inherent to nocturnal penile tumescence recording by Snap-Gauge as opposed t o the Rigiscan.* These investigators report a direct correlation between impotence after transurethral resection of the prostate and patient age, and an indirect correlation between it and the size of the adenoma resected. The latter finding is unique and underscores the need for informed consent in younger patients with small adenomas. Additionally, it further supports the need to implement aggressively alternative medical and interventional therapies in these patients before choosing transurethral resection of the prostate. The exact etiology of the organic erectile dysfunction resulting in impotence after transurethral resection of the prostate appears to be related to the initiation or worsening of preexisting corporeal veno-occlusive dysfunction.4 The corporeal veno-occlusive dysfunction may result from direct thermoelectric or coagulative electrocautery injury to the erectile tissue, a similar injury to the cavernous nerves that lie ad-
Upper limit [mean + 3 standard devlations) of normal values for perception thresholds in a population of potent men
1494
* Dacomed, Minneapolis,
Minnesota.
1495
ERECTILE DYSFUNCTION jacent to t h e prostatic capsule, or extravasation of irrigating fluid and t h e subsequent inflammatory reaction producing nerve or corporeal tissue injury.4 These pathogenic mechanisms may be more likely to occur during resection of a small gland.
Harin Padma-Nathan Department of Urology University of Southern California Medical Center Los Angeles, California
REFERENCES
1. Padma-Nathan, H.: Neurologic evaluation of erectile dysfunction. Urol. Clin. N. h e r . , 1 6 77, 1988. 2. Porst, H.: Prostaglandin E l and the nitric oxide donor linsidomine for erectile failure: a diagnostic comparative study of 40 patients. J. Urol., part 2, 149 1280, 1993. 3. Padma-Nathan, H., Keller, T., Poppiti, R., Lue, T., Tam, P. and Place, V.: Hemodynamic effects of intraurethral alprostadil the medicated urethral system for erection (MUSE).J. Urol., part 2,161: 345A, abstract 469, 1994. 4. Padma-Nathan, H., and Goldstein, I.: The pathogenisis of postl " impotence. J. Urol., part 2,139 2754 abstract 449,1988.