Theoretical and Technical Problems in the Measurement of Nocturnal Penile Tumescence for the Differential Diagnosis of Impotence 1

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1 Theoretical and Technical Problems in the Measurement of Nocturnal Penile Tumescence for the Differential Diagnosis of Impotence 1 MARVIN D. WASSERMAN, MD, CHARLES P. POLLAK, MD, ARTHUR J. SPIELMAN, PHD, AND ELLIOT D. WEITZMAN, MD Theoretical and technical problems in using Nocturnal Penile Tumescence (NPT) measurements for the differential diagnosis of impotence are discussed and possible solutions are offered: 1) The basic assumption that NPT measurements can distinguish psychogenic from organic impotence has never been demonstrated in patients shown to be psychogenically and organically impotent independent of the NPT measurements themselves. Studies attempting to do this are necessary to determine definitively the limits of the clinical applicability of this important diagnostic tool. 2) Evidence is presented showing that though a direct observation of one of the patient's fullest erections is required for an adequate NPT evaluation, this is not always done. The danger of misdiagnosis if this step is omitted is illustrated with a case report. 3) Disagreements in the literature about NPT criteria for diagnosing psychogenic impotence are discussed and criteria are suggested that are based on demonstrating the intactness of the physiological mechanisms required for erection rather than on values recorded in normal subjects. INTRODUCTION The often difficult determination of whether a patient's impotence is psychogenic, organic, or mixed 2 has become of greater practical importance 'This is a modified version of a paper presented at the Symposium: Sleep Studies in the Diagnosis of Impotence. Meeting of American Psychosomatic Society, March 23, Although we diagnose a patient as "psychogenically" or "organically" impotent for clinical and discussion purposes, such pure diagnostic categories do not exist. Penile erection is the end product of a complex interaction of physiological and psychological processes and a disturbance in erectile function invariably involves both. A discussion of our criteria for diagnosing psychogenic, organic, and mixed impotence is found below. From the Sleep-Wake Disorders Center, Departments of Psychiatry and Neurology, Montefiore Hospital and Medical Center, Albert Einstein College of Medicine, Bronx, New York. Address requests for reprints to: Dr. Marvin D. Wasserman, Sleep-Wake Disorders Center, Montefiore Hospital, 111 East 210 Street, Bronx, NY Received for publication March 25, 1980; revision received August 16, since in recent years there have been advances in the treatment of both psychogenic (1, 2) and organic impotence (3-6). Simultaneous with these therapeutic advances, the measurement of Nocturnal Penile Tumescence (NPT) has come into use as a means of helping to make this important differential diagnosis (7 19). This article briefly reviews the literature on both the use of NPT measurements in the differential diagnosis of impotence and the evidence demonstrating that psychogenic factors can inhibit NPT, focuses for the first time on the theoretical and technical problems in the use of NPT measurements for the differential diagnosis of impotence, and offers suggestions as to how these problems might be resolved. REVIEW OF LITERATURE In 1944 Ohlmeyer et al. (20) described a cycle of penile erections during sleep in men 20 to 40 years old. In 1953, Aserinsky Psychosomatic Medicine Vol. 42, No. 6 (November 1980) Copyright 1980 by the American Psychosomatic Society, Inc. Published by Elsevier North Holland, Inc. 52 Vanderbilt Ave., New York, NY /80/ $01.75

2 MARVIN D. WASSERMAN et al. and Kleitman (21) first described Rapid Eye Movement (REM) sleep, and in 1955 they noted that the length of nocturnal erections appeared to correspond to the length of REM periods during normal sleep (22). During the mid-1960s Fisher ct al. (23) and Karacan et al. (24) independently demonstrated that 80-95% of REM periods of men in their 20s and 30s were accompanied by full or partial erections. Subsequently, Karacan et al. (8, 9, 25-28) reported that all normal males from 3 to 79 years old had NPT during normal sleep, the amount being a function of age. In 1970, Karacan (7) first reported using NPT measurements to distinguish psychogenic from organic impotence, providing for the first time an objective measure to aid the clinician in making this often difficult distinction. It was assumed that the relevant psychological factors would be inoperative during sleep in psychogenically impotent men and NPT would therefore be present. In organically impotent men, NPT would be absent, since the organic mechanisms would continue to operate even during sleep. Using these assumptions, a group of clinically indistinguishable impotent diabetics was divided into two distinct groups based on the presence or absence of NPT. Subsequently, Karacan et al. have indicated that NPT can be impaired to varying degrees (10, 11), but continue to report that NPT provides an objective basis to distinguish organic from psychogenic impotence (8-13). Fisher et al. (14) also suggested that NPT measurements could be used to help differentiate organic from psychogenic impotence, but stressed the necessity of a comprehensive clinical evaluation in conjunction with NPT recordings and raised the possibility that some psychogenic cases might have impaired NPT. It is of interest in this regard that 20% of the patients with impaired NPT studied by Karacan had no demonstrable organic disease known to cause impotence. He believes that these patients may have subtle physiological deficits not detectable by available techniques (29), whereas Fisher et al. (14-17) and Wasserman et al. (18) have raised the possibility that at least some of these patients may have psychogenic impotence. The following findings demonstrate that psychological factors can inhibit NPT and, therefore, raise the possibility that NPT may be significantly impaired in some psychogenically impotent patients. Several studies showed impaired NPT associated with anxiety dreams or anxiety caused by the recording situation. Karacan et al. found that NPT was impaired or absent in normal men during REM periods that were associated with dreams with a high anxiety content (24). Fisher (30) similarly found that erections were impaired in normal men in association with dreams that had a manifest content containing aggression, anxiety, or other negative affects. Jovanovic reported decreased total tumescence time, a decreased number of tumescence episodes, and a preponderance of weak and moderate episodes over stronger episodes on the first night of recording in the sleep laboratory as compared to the second night (31). This "first night effect" is presumably due to the novelty of the recording situation and the anxiety associated with it. Other studies have shown differences between NPT in normal and psychogenically impotent subjects. Fisher et al. (14) found a marked discrepancy between the impaired waking erections and the relatively 576 Psychosomatic Medicine Vol. 42, No. 6 (November 1980)

3 DIFFERENTIAL DIAGNOSIS OF IMPOTENCE BY NPT intact NPT in men diagnosed psychogenically impotent. However, careful review of their data indicates some decreases compared to normals in total nightly duration and length of episodes of NPT, as well as an increased tendency for the tumescence episodes to be interrupted early. Karacan et al. (10) found that 11 psychogenically impotent patients spent more time in and had a larger number of parital erections than 11 age-matched normal subjects. The psychogenically impotent patients also had fewer full erections per night (2.00 ± 0.95 compared to 2.59 ± 1.1), but the difference was not statistically significant. Finally, several studies have shown impaired NPT in patients whose total clinical picture indicated that physiological mechanisms for erection were intact. Kahn and Fisher (32) described two otherwise normal subjects between 71 and 96 years old who did not have full nocturnal erections when recorded in a sleep laboratory but reported being able to have intercourse. One of these, a 76-year-old subject, was recorded for 5 nights without an erection, but he reported successful intercourse every 1 to 2 months. Jovanovic (cited by Fisher (14)) noted a reduction in the number of erections, a 45% decrease in total nightly duration of erections, and a complete absence of full erections in 53 men diagnosed on clinical grounds to be psychogenically impotent. However, these results have not been replicated. Fisher et al. described three patients with significant impairment of NPT but no evidence of organic disease. They felt that they were psychogenically impotent despite the NPT findings. One of them was recorded for 4 nights with virtually no NPT. He was observed to attain a 90% erection by masturbating on the morning following the fourth night's recording. One year later he was still able to get a full erection when he masturbated but not when he attempted intercourse (17). THEORETICAL AND TECHNICAL PROBLEMS Basic Assumption Questioned In 1970 Karacan (7) first reported using NPT monitoring for the differential diagnosis of impotence. He assumed that if the pptient was psychogenically impotent nocturnal erections would be present since the psychogenic factors would be inoperative during sleep, and that if the patient was organically impotent nocturnal erections would be absent since the organic factors would continue to operate even during sleep. He recorded NPT in clinically indistinguishable impotent diabetics who were then diagnosed as psychogenically or organically impotent based on the presence or absence of NPT. Subsequently, Karacan et al. have described degrees of NPT impairment (10, 11), but continue to report that NPT provides an objective basis for distinguishing psychogenic from organic impotence (8 13). Although clinical experience strongly suggests that NPT monitoring is useful as an aid for the differential diagnosis of impotence in most cases, the assumption that NPT can distinguish psychogenic from organic impotence has never been validated in patients shown to be psychogenically or organically impotent independent of the NPT measurements themselves. Studies attempting to validate this basic assumption are therefore necessary to definitively determine whether NPT is useful for all cases of Psychosomatic Medicine Vol. 42, No. 6 (November 1980) 577

4 MARVIN D. WASSERMAN et al. impotence, and if not, to identify the exceptions. At present, both because of the lack of definitive validation of the basic assumption and the evidence cited above suggesting that some psychogenically impotent patients may have significantly impaired NPT, the diagnosis of organic impotence should not be made solely on the basis of significantly impaired NPT measurements. This caution is especially necessary since such a diagnosis often carries with it a recommendation for surgical implantation of a penile prosthesis. To be diagnosed as organically impotent, in addition to having significantly impaired NPT, the patient should have evidence of an organic disease known to cause impotence and a history that does not strongly suggest a psychogenic etiology, e.g., full erections in some circumstances but not others. The ability of NPT measurements to discriminate psychogenic from organic impotence could be tested by recording NPT prior to treatment in subjects selected because their clinical picture strongly suggested reversible psychogenic or organic impotence. The reversibility by specific psychological and organic treatments would provide evidence independent of NPT measurements about the cause of the impotence. The NPT results could then be analyzed to determine to what degree they discriminated the two groups. Requirement for Direct Observation of an Erection There are large interindividual differences in the increase in circumference associated with full erections at the tip of the penis (10-48 mm) (13, 26) as well as at the base (15-45 mm) (16, 17). Because of this, there is general agreement that if the increase in circumference falls within the above ranges, the only way at present to determine whether the erection is adequate for vaginal penetration is to observe it directly and test its rigidity (17, 18, 33). An adequate observation is the most difficult step in the NPT evaluation. This is because it is sometimes not possible to time the awakening so that the observed erection is sufficiently rigid for vaginal penetration and/or the increases in circumference at both the base and tip of the penis are 81% or more of the largest increases recorded during the 3 nights (the increase in normals shown to usually be associated with an erection sufficiently rigid for vaginal penetration (11)). If an adequate awakening is not possible, an alternative employed in our center, as well as by Fisher et al. (17), is to have the patient masturbate with a strain gauge in place at the base of his penis. An observation is made, if possible, when the increase in circumference reaches 81% or more of the largest increase recorded during sleep. The difficulty in obtaining an adequate observation may explain why in practice a direct observation has not always been used to determine if an erection is full. For example, in a study in which most of the patients who had increases in circumference of 5 mm or more at the tip were awakened to observe one or more of their fullest erections, an erection was classified as full or partial based on the amount of increase in circumference and not on information obtained from the direct observation. An increase of 16 mm or more at the tip was defined as a full erection (11). In other studies the erections were not directly observed (34, 35). A clinical example illustrates the potential hazards of basing a diagnosis sole- 578 Psychosomatic Medicine Vol. 42, No. 6 (November 1980)

5 DIFFERENTIAL DIAGNOSIS OF IMPOTENCE BY NPT ly on circumference changes. Patient I 3 is a 49-year-old married white male with a history of progressive erectile impairment for 3 years prior to our evaluation. Two years prior to coming to our center, he consulted a urologist who found no abnormality other than a small inguinal hernia and referred the patient for sex therapy. The patient remained convinced that his problem was organic in origin, consulted a second urologist who found a borderline abnormal glucose tolerance test (GTT), and then consulted a diabetologist who did not think that his impotence was secondary to diabetes. Following this consultation the patient went on a vacation with his wife and was able to have intercourse three times during a one week period. Subsequent to this transient improvement, there was again further steady deterioration and the patient was unable to obtain an erection sufficient for intercourse in the month prior to coming to our center. His sexual desire was also markedly decreased. Physical and neurological examinations were normal. NPT was recorded for 3 consecutive nights. His largest increase in circumference at the base was 21 mm and at the tip was 14 mm. Both values fall within the normal range for full erections cited earlier. However, when an erection with an increase at the base of 17 mm, representing 81% of the largest increase in circumference at the base during the 3 nights, and an increase at the tip of 14 mm, the largest increase at the tip during the 3 nights, was observed, both patient and observer felt it was inadequate for vaginal 3 This patient was described briefly in a previous publication (18). penetration. They both rated it as 5 to 6 on a 0 to 10 scale, with 8 defined as sufficently rigid for intercourse. The results of recording sleep and NPT are summarized in Table 1. The number of and time spent in maximum erections (full erections) as well as the number of erections sustained in the maximum range for 5 or more minutes are shown calculated on the basis of circumference increase alone, and on the basis of both circumference increase and the results of a direct observation. If the diagnosis had been solely based on circumference changes, the patient's erections would have been considered to be full resulting in a mistaken diagnosis of psychogenic impotence and his again being referred for psychotherapy. The direct observation demonstrated that this was not the case. Abnormal laboratory tests were as follows: GTT: fasting blood sugar (FBS) 88 mg/dl, 30 min 152 mg/dl, 1 hr 213 mg /dl, 2 hr 135 mg /dl, 3 hr 72 mg /dl, 4 hr 70 mg/dl, 5 hr 77 mg/dl; testosterone 184 ng/100 ml ( ng/100 ml); prolactin 461 ng/nl (5-18 ng/ml); luteinizing hormone (LH) 2.7 mlu/ml (7-24 mlu/ml); follicle stimulating hormone (FSH) 3.4 mlu/ml (4-25 mlu/ml). Normal laboratory tests included: complete blood count, blood serology, SMA - 12, T - 4, urinalysis, EKG, chest X-ray, penile blood pressure, skull X-ray, polytomograms of the sella turcica, and CAT scan of the brain. The patient was considered to probably have a pituitary microadenoma that was not demonstrated by radiographic techniques. He was treated for hyperprolactinemia with bromocryptine mesylate starting with 2.5 mg/day. This was increased by 2.5 mg increments every 10 Psychosomatic Medicine Vol. 42, No. 6 (November 1980) 579

6 MARVIN D. WASSERMAN et al. TABLE 1. NPT Measurements in Patient 1 before and after Treatment with Bromocryptine Mesylate Sleep Average total sleep time/night (min) Average total REM time/night (min) Average REM % of total sleep time/night Total number of REM periods NPT Total number of REM erections base tip Largest increase in circumference (mm) base tip Total number of maximum REM erections base tip Total time spent in maximum REM erection (min) base tip Total number of erections sustained in the maximum range for 5 or more min base tip 3 Night Evaluation Before Bromocryptine % M0) b 1 MO) b 22MO) b 11.3M0) b 1 MO) b 1 MO) b Awakening Increase in circumference at time of awakening (mm) (Percentage of largest increase in circumference during 3 nights' recording) base 17(81%) tip 14(100%) Rating of observed erection patient 5-6/10 observer 5-6/10 3 Night Evaluation After Bromocryptine % c 28 c (2) b c (9.3) b 28(100%) 8/ /10 a The value noted was based on circumference increase alone. A maximum erection was defined as an erection which had an increase of 81% or more of the largest increase in circumference recorded during the three nights. b The value noted in parentheses was based both on circumference increase and direct observation. A maximum erection is defined as an erection which had an increase of 81% or more of the largest increase in circumference recorded during the three nights and which was confirmed by direct observation to be adequate for intercourse. c Tip was not recorded because of technical difficulties. 580 Psychosomatic Medicine Vol. 42, No. 6 (November 1980)

7 DIFFERENTIAL DIAGNOSIS OF IMPOTENCE BY NPT days until he reported a complete return of potency, 2 3 days after increasing his daily dose to 10 mg. Five months later, while the patient was continuing 10 mg/day of bromocryptine mesylate NPT was re-recorded for 3 consecutive nights. Laboratory tests done at that time revealed the following: prolactin 14 ng/ml (5-18 ng/ml); LH 10 mlu/ml (7-24 mlu/ml); FSH 4.1 mlu/ml (4-25 mlu/ml); all of them had returned to normal. Testosterone was still reduced however, 215 ng/100ml ( ng/100ml). The NPT recordings showed that the largest increase in circumference at the base was 28 mm. An awakening at that time revealed a fully rigid "standup" erection that both patient and observer felt was adequate for intercourse. The sleep and NPT results of these recordings are also summarized in Table 1. The patient had only one maximum erection sustained for 5 or more minutes, illustrating that a man with a history of unimpaired erectile functioning n^y have only one such erection during 3 nights of NPT recording. NPT Criteria for Diagnosing Psychogenic Impotence All previous attempts to classify impotence as psychogenic or organic based on NPT measurements have relied to some degree on reported normal values. However, there is disagreement about which normal values should be used, i.e., should frequency of full erections and/or duration of full erections be used, should data from all erections or only full erections be used. There is also disagreement about whether different criteria should be used for patients of different ages, and whether the criteria for diagnosing psychogenic impotence should be based entirely or only partially on normative data. Examples of NPT criteria that have been used to diagnose psychogenic impotence include: 1) one or more full NPT episodes (11), 2) one maximum (full) erection per night that is maintained for 5 or more minutes (17), and 3) "total minutes and number of full episodes within the normal range" (13). These difficulties in arriving at NPT criteria for diagnosing psychogenic impotence have led us to question the usefulness of reported normal NPT values for the diagnosis of impotence, since Karacan et al. (17, 24, 33), Fisher et al. (16, 17, 30), Jovanovic (31), and Wasserman et al. (18) agree that psychological factors can inhibit NPT. Any disagreement concerns not whether, but to what degree psychological factors inhibit nocturnal erections. We concur with Kaplan (2) that psychogenic impotence is always caused by the complex interaction of psychological and physiological factors and is never the result of psychological factors alone. With this in mind, we began by asking what are we trying to demonstrate when we measure NPT that will justify diagnosing a patient psychogenically impotent. We concluded that the goal is to demonstrate that the patient has sufficient physiological capacity to attain an erection sufficiently rigid for vaginal penetration and to maintain it for a period of time sufficiently long for satisfactory intercourse. The purpose is not to determine if he can equal values for frequency and/or duration of full and /or partial erections of age-matched potent normals. Looked at in this way, the question becomes, what NPT findings demonstrate the physiological capacity to attain and maintain an erection adequate for satisfactory intercourse, rather than how normal NPT is defined. We have operationally defined impo- Psychosomatic Medicine Vol. 42, No. 6 (November 1980) 581

8 MARVIN D. WASSERMAN et al. tence as "psychogenic" if the patient has one or more full erections during the 3 nights of NPT recording confirmed by direct observation to be adequate for vaginal penetration and maintained with this degree of rigidity for 5 or more consecutive minutes. The occurrence of such an erection even once during the three nights of recording demonstrates that the physiological mechanisms for erection during sleep are sufficiently intact for the patient to attain and maintain a full erection. The clinical usefulness of this finding is based on the assumption that the same physiological mechanisms for erection operate during both waking and sleep. This assumption needs to be validated. The duration of 5 minutes originally suggested by Fisher et al. (17), was chosen because of our clinical impression that this period is sufficiently long for satisfactory intercourse for most men. In addition to "psychogenic" impotence we have also developed three other categories in our system of classifying impotence: 1. "Organic". The patient has no full erections during 3 nights' recording, independent evidence of an organic disease known to cause impotence, and the absence of a history strongly suggestive of a psychogenic etiology, e.g., full erections in some circumstances but not in others. 2. Mixed. The patient has one or more full erections during the 3 nights' recording confirmed by direct observation to be adequate for vaginal penetration but none are maintained in the maximum range for 5 or more consecutive minutes, independent evidence of an organic disease known to cause impotence, and a history strongly suggestive of a psychogenic component, e.g., brief (less than 5 minutes) full erections in some circumstances but not in others. 3. Undetermined origin. The patient has one or more erections with an increase of 10 mm or more at the tip or 15 mm or more at the base, but an adequate direct observation is not possible to determine whether these erections are sufficiently rigid for vaginal penetration, or if the patient has no full erections during the 3 nights' recording and there is no independent evidence of an organic disease known to cause impotence. On the basis of these criteria we have diagnosed the first 25 patients evaluated in our Center (Table 2). Only one patient was diagnosed as "mixed." Because of our limited experience with such patients, the criteria described above for making this diagnosis are considered tentative. Although impotence of "mixed" etiology is mentioned in the literature (14, 18, 36, 37) as a possibility, there have been no published case reports of such patients. A case report of the patient we diagnosed as "mixed" is in preparation for publication. The data regarding changes in circumference at the base and tip, the total number of maximum erections and the number of maximum erections that were maintained for 5 or more consecutive minutes in each of the eleven patients we have diagnosed as "psychogenically" impotent is shown in Table 3. TABLE 2. Diagnosis Psychogenic Organic Mixed Undetermined Diagnostic Classification of Impotent Patients Number of Patients Psychosomatic Medicine Vol. 42, No. 6 (November 1980)

9 DIFFERENTIAL DIAGNOSIS OF IMPOTENCE BY NPT TABLE 3. Maximum Erections in Psychogenically Impotent Patients during 3 Consecutive Nights of NPT Recording Patient Number Total Number of Maximum Erections a B-7 T-6 B-10 T-2 B-4 T-14 B-W> T-8 b B-11 T-8 B-6 T-4 B-6 T-2 B-4 T-2 B-15 T-8 B-2 T-1 B-5 b T-4 b Number of Maximum Erections Maintained for 5 or more Consecutive Minutes B-5 T-1 B-7 T-1 B B-4b T-6b B B-4c T_2d B-3 T-1 B-3 T-1 B-7 T-2 B-1 T-1 a B = base; T = Tip. b Maximum erection calculated on basis of an increase in circumference of less than 81% of largest increase in circumference for the 3 nights because a smaller increase was shown by direct observation to be adequate for vaginal penetration. c Recorded only 2 nights because of technical difficulties. d Recorded only 1 night because of technical difficulties. SUMMARY Cr Cr Theoretical and technical problems in using NPT measurements for the differential diagnosis of impotence are discussed. It has been assumed that NPT measurements can discriminate between psychogenically and organically impotent patients. However, the validity of this assumption has never been demonstrated in patients shown to be psychogenically or organically impotent independent of NPT measurements. Studies to test this assumption are required to definitively determine the limits of the clinical applicability of this important diagnostic tool. Inconsistencies in the literature about the necessity of directly observing one of the patient's fullest erections to determine if it is sufficiently rigid for vaginal penetration are discussed. It is concluded that because of the high interindividual variability in the increase in circumference associated with an erection sufficiently rigid for vaginal penetration, it is necessary that a direct observation be performed in all patients whose increase is within the range reported to be associated with full erections. A patient is described who would have been misdiagnosed if this step had been omitted. Disagreements in the literature about NPT criteria for diagnosing psychogenic impotence are discussed. All of the previously suggested criteria rely to a greater or lesser extent on normal values. We suggest that NPT criteria should be focused on demonstrating that physiological mechanisms required for erection are sufficiently intact for the patient to attain and maintain an erection adequate for intercourse rather than on showing that the patient can equal reported values for age-matched normal subjects. We recommend that the criterion for such physiological intactness of erectile mechanisms is the occurrence during 3 nights' recording of one full erection maintained for 5 or more consecutive minutes. Psychosomatic Medicine Vol. 42, No. 6 (November 1980) 583

10 MARVIN D. WASSERMAN et al. REFERENCES 1. Masters WH, Johnson VE: Human Sexual Inadequacy. Boston, Little, Brown, 1970, pp Kaplan HS: The New Sex Therapy. New York, Bruner Mazel, 1974, pp Scott FB, Bradley WE, Timm CW: Management of erectile impotence. Use of implantable inflatable prosthesis. Urology 2: 80-82, Small MP, Carrion HM, Gordon JA: Small-Carrion penile prosthesis. Urology 5: , Michal V, Kramar R, Bartak V: Femoro-pudendal by-pass in the treatment of sexual impotence. J Cardiovasc Surg 15: , Scott FB, Byrd GJ, Karacan I, Olsson P, Beutler LE, Attia SL: Erectile impotence treated with an implantable, inflatable prosthesis. J Am Med Assoc 241: , Karacan I: Clinical value of nocturnal erection in the prognosis and diagnosis of impotence. Med Aspects Hum Sex 4: 27-34, Karacan I, Williams RL, Thornby JI, Salis PJ: Sleep related tumescence as a function of age. Am J Psychiatry 132: , Karacan I, Salis PJ, Thornby JI, Williams RL: The ontogeny of nocturnal penile tumescence. Waking and Sleeping 1: 27-44, Karacan I, Scott FB, Salis PJ, Attia SL, Ware JC, Attila A, Williams RL: Nocturnal erections, differential diagnosis of impotence, and diabetes. Biol Psychiatry 12: , Karacan I, Salis PJ, Ware JC, Dervent B, Williams RL, Scott FB, Attia SL, Beutler LE: Nocturnal penile tumescence and diagnosis in diabetic impotence. Am J Psychiatry 135: , Karacan I: Advances in the psychophysiological evaluation of male erectile impotence, in Handbook of Sex Therapy. Edited by J LoPiccolo, L LoPiccolo. New York, Plenum Publishing, 1978, pp Karacan I, Salis PJ, Williams RL: The role of the sleep laboratory in diagnosis and treatment of impotence, in Sleep Disorders, Diagnosis and Treatment. Edited by RL Williams, I Karacan. New York, John Wiley and Sons, 1978, pp Fisher C, Schiavi R, Lear H, Edwards A, Davis DM, Witkin BA: The assessment of nocturnal REM erection in the differential diagnosis of sexual impotence. J Sex Marriage Ther 1: , Fisher C, Schiavi R, Edwards A: Assessment of nocturnal REM erection in differential diagnosis of sexual impotence. Sleep Res 5: 42, Fisher C, Schiavi R, Edwards A, Davis D, Reitman M, Fine J: Quantitative differences in nocturnal penile tumescence (NPT) between impotence of psychogenic and organic origin. Sleep Res 6: 49, Fisher C, Schiavi RC, Edwards A, Davis D, Reitman M, Fine J: Evaluation of nocturnal penile tumescence in the differential diagnosis of sexual impotence. Arch Gen Psychiatry 36: , Wasserman MD, Pollak CP, Spielman AJ, Weitzman ED: The differential diagnosis of impotence: measurement of noctural penile tumescence. J Am Med Assoc 243: , Wasserman MD, Pollak CP, Spielman AJ, Weitzman ED: Impaired nocturnal erections and impotence following transurethral prostatectomy. Urology 15: , Ohlmeyer P, Brilmayer H, Hullstrung H: Periodische vorgange im schlaf. Pflueggers Arch 248: , Aserinsky E, Kleitman N: Regularly occurring periods of eye motility and concomitant phenomena during sleep. Science 118: , Aserinsky E, Kleitman N: Two types of ocular motility occurring in sleep. J Appl Physiol 8:1-10, Fisher C, Gross J, Zuch J: Cycle of penile erection synchronous with dreaming (REM) sleep. Arch Gen Psychiatry 12: 29-45, Karacan I, Goodenough DR, Shapiro A, Starker S: Erection cycle during sleep in relation to dream anxiety. Arch Gen Psychiatry 15: , Karacan I, Hursch CJ, Williams RL, Thornby JI: Some characteristics of nocturnal penile tumescence in young adults. Arch Gen Psychiatry 26: , Hursch CJ, Karacan I, Williams RL: Some characteristics of nocturnal penile tumescence in early middle-aged males. Comp Psychiatry 13: , Karacan I, Hursch CJ, Williams RL, Littell RC: Some characteristics of nocturnal penile tumescence during puberty. Pediat Res 6: , Psychosomatic Medicine Vol. 42, No. 6 (November 1980)

11 DIFFERENTIAL DIAGNOSIS OF IMPOTENCE BY NPT 28. Karacan I, Hursch CJ, Williams RL: Some characteristics of nocturnal penile tumescence in elderly males. J Gerontol 27: 39-45, Impotence: Psyche vs. soma. Med World News: 17: 28, June 28, Fisher C: Dreaming and sexuality, in Psychoanalysis A General Psychology. Edited by RM Loewenstein, LM Newman, M Schur, AJ Solnit. New York, Int Univ Press, 1966, pp Jovanovic VJ: Der effekt der ersten untersuchungsnacht auf die erektionen im schlaf. Psychother Psychosom 17: , Kahn E, Fisher C: REM sleep and sexuality in the aged, J Geriatr Psychiat 2: , Karacan I, Ilaria RL: Nocturnal penile tumescence (NPT): the phenomenon and its role in the diagnosis of impotence. Sexuality Disability 1: , Hosking DJ, Bennett T, Hampton JR, Evans DF, Clark AJ, Robertson G: Diabetic impotence: studies of nocturnal erection during REM sleep. Br Med J 2: , Madorsky ML, Ashamalla MG, Schussler I, Lyons HR, Miller GH: Postprostatectomy impotence. J Urol 115: , Karacan I, Ware JC, Dervent B, Attila A, Thornby JI, Williams RL, Kaya N, Scott, FB: Impotence and blood pressure in the flaccid penis: relationship to nocturnal penile tumescence. Sleep 1: , Karacan I, Dervent A, Cunningham G, Moore CA, Weinstein EJ, Cleveland SE, Salis PA, Williams RL, Kopel K: Assessment of nocturnal penile tumescence as an objective method for evaluating sexual functioning in ESRD patients. Dialysis Transplant 7: , 890, 1978 Psychosomatic Medicine Vol. 42, No. 6 (November 1980) 585

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