The low-dose dexamethasone suppression test: a reevaluation in patients with Cushing's syndrome

Low-dose dexamethasone suppression testing has been recommended for biochemical screening when Cushing's syndrome is suspected. The criterion for normal suppression of cortisol after dexamethasone is controversial. To assess diagnostic utility (sensitivity), we report the results of low-dose dexamethasone suppression testing in 103 patients with spontaneous Cushing's syndrome. There were 80 patients with Cushing's disease (78%), 13 with the ectopic ACTH syndrome (13%), and 10 with cortisol-producing adrenocortical adenomas (10%). Fourteen (18%) of 80 patients with Cushing's disease suppressed serum cortisol to less than 5 micro g/dl (<135 nmol/liter) after the overnight 1-mg test, whereas six patients (8%) actually showed suppression of serum cortisol to less than 2 micro g/dl (<54 nmol/liter). In addition, the 2-d, low-dose dexamethasone suppression test yielded false-negative results in 38% of patients when urine cortisol was used and 28% when urinary 17-hydroxycorticosteroids were used. Serum cortisol after the 1-mg test correlated with baseline urinary free cortisol (r = 0.705, P < 0.001), plasma ACTH level (r = 0.322, P = 0.001), and urinary free cortisol after the 2-d test (r = 0.709, P = 0.001). This study provides evidence that low-dose dexamethasone may suppress either plasma cortisol or urinary steroids to levels previously thought to exclude Cushing's syndrome and that these tests should not be used as the sole criterion to exclude the diagnosis of endogenous hypercortisolism.     

Endogenous Cushing's syndrome: clinical and laboratorial features in 73 cases

We studied clinical and laboratorial features of 73 patients with endogenous Cushing's syndrome, subdivided as follows: 46 (63%) with Cushing's disease (CD), 21 (28.7%) with an adrenal tumor and 6 (8.2%) with ectopic ACTH secretion (EAS). The rate of typical manifestations of hypercortisolism was similar regardless its etiology. In 100% of cases of Cushing's syndrome we observed serum cortisol levels greater than 1.8 microg/dL in low-dose dexamethasone (DMS) suppression tests, as well as elevation of serum or salivary midnight cortisol. However, urinary free cortisol was normal in 11.5% of patients. ACTH levels were suppressed in patients with adrenal tumors, normal or high in CD and always high in EAS. In the 8-mg overnight DMS suppression test, serum cortisol suppression > 50% was observed in 78.2% of cases of CD and in 33.3% of subjects with EAS, while an 80% suppression was only seen in CD. After stimulation with CRH or DDAVP an ACTH increase > 35% occurred in 81% of individuals with CD and 16.6% of those with EAS, while an ACTH increase > 50 achieved 100% specificity. Moreover, the combination of serum cortisol suppression > 50% and an ACTH increase > 35% in both tests only occurred in Cushing's disease. Pituitary magnetic resonance imaging identified 100% of macroadenomas and 59.4% of microadenomas in patients with CD. Among 10 patients that underwent bilateral inferior petrosal sinus sampling, a central-to-peripheral ACTH gradient > 3 after CRH or DDAVP had 90% sensitivity and 100% specificity for Cushing's disease.     

过夜小剂量地塞米松抑制试验对库欣综合征诊断价值的再探讨

目的重新探讨过夜小剂量地塞米松抑制试验对库欣综合征的诊断价值。方法回顾性分析我院1990年1月到2005年7月收治的52例库欣综合征患者和153例经住院检查排除库欣综合征的肥胖症和高血压病患者，比较过夜小剂量（1mg）地塞米松抑制试验的不同血清皮质醇切点对库欣综合征诊断的敏感性和特异性。结果在过夜1mg地塞米松抑制试验中，以试验当日晨8：00血清皮质醇为基础值，次日8：00血清皮质醇为基础值的50％以及次日晨8：00血清皮质醇275、200、138和50nmol／L为切点，诊断库欣综合征的敏感性分别为92．3％、92．3％、92．3％、92．3％和100．0％，特异性分别为90．8％、98．7％、96．1％、91．5％和78．4％。结论在过夜1mg地塞米松抑制试验中，以次日晨8：00血清皮质醇50nmol／L为切点具有较高的敏感性，可作为库欣综合征的第一线筛选试验。     

The continuous 7-hour intravenous dexamethasone suppression test in the differential diagnosis of ACTH-dependent Cushing''s syndrome

OBJECTIVE: A recent report showing disappointingly low sensitivity and specificity for the oral high dose dexamethasone test in the differential diagnosis of Cushing's syndrome prompted us to re-evaluate the results obtained in our centre using the continuous 7-hour intravenous dexamethasone suppression test for this purpose. PATIENTS: 105 patients with ACTH-dependent Cushing's syndrome were included in this study; 78 with Cushing's disease, 8 with ectopic ACTH-secreting tumours and 19 were classified as 'of unknown aetiology'. RESULTS: In 74/78 (94.9%) of patients with Cushing's disease and in 3/8 (37.5%) patients with the ectopic ACTH syndrome, a plasma cortisol decrease > 190 nmol/l at 7 h as compared to baseline values was achieved in the continuous 7-hour intravenous dexamethasone suppression test. Using a plasma cortisol decrease > 190 nmol/l at 7 h as compared to baseline values as the cut-off value, the sensitivity and specificity of the continuous 7-hour intravenous dexamethasone suppression test for the diagnosis of Cushing's disease in patients with ACTH-dependent Cushing's syndrome were 94.9% and 62.5%, respectively. CONCLUSIONS: In patients with ACTH-dependent Cushing's syndrome with a plasma cortisol decrease > 190 nmol/l at 7 h in the continuous 7-hour intravenous dexamethasone suppression test, additional localizing investigations such as bilateral simultaneous inferior petrosal sinus sampling and/or pentetreotide scintigraphy should be performed when no clearly discernible pituitary adenoma is observed on MRI studies. Patients with ACTH-dependent Cushing's syndrome with a plasma cortisol decrease < 190 nmol/l at 7 h in the continuous 7-hour intravenous dexamethasone suppression test should also undergo bilateral simultaneous inferior petrosal sinus sampling and/or pentetreotide scintigraphy to demonstrate the presence of a nonpituitary source of ACTH overproduction.     

An overnight high-dose dexamethasone suppression test for rapid differential diagnosis of Cushing's syndrome

We have developed a high-dose dexamethasone suppression test that can be administered overnight with a single 8-mg dose and used the new procedure in the differential diagnosis of 83 patients with Cushing's syndrome. In 76 patients with surgically or pathologically proven cause--60 with Cushing's disease, 7 with the ectopic adrenocorticotrophic hormone syndrome, and 9 with adrenal tumors--suppression of plasma cortisol levels to less than 50% of baseline indicated a diagnosis of Cushing's disease. The test had a sensitivity of 92%, a specificity of 100%, and a diagnostic accuracy of 93%. These values equal or exceed those of the standard 2-day test whether based on suppression of urinary 17-hydroxycorticosteroids or plasma cortisol. We conclude that this overnight, high-dose dexamethasone suppression test is practical and reliable in the differential diagnosis of Cushing's syndrome.     

Effect of glycemic control on the overnight dexamethasone suppression test in patients with diabetes mellitus.

Because many of the clinical features associated with Cushing's syndrome are frequently found in patients with diabetes mellitus, diabetic patients are often evaluated for Cushing's syndrome. The initial test for Cushing's syndrome is the 1 mg overnight dexamethasone suppression test (DST), but its value as a screening test in diabetic subjects, especially those with poor glycemic control, has been questioned. To address this issue, an overnight DST was administered to 100 subjects with diabetes. Only 7 patients failed to suppress their plasma cortisol to less than 140 nmol/L (5.0 micrograms/dL), achieving a specificity of 93%. There was no relation between acute glycemic control (as measured by the mean of 4 serum glucose values obtained before receiving dexamethasone) or chronic glycemic control (as measured by glycohemoglobin) and false positive responses to the 1 mg overnight DST. The mean of the measures of acute glycemic control of the 7 subjects who had false positive results, 14.4 +/- 2.8 mmol/L, was not significantly different than that of the 93 subjects with normal responses, 13.2 +/- 3.3 mmol/L. Similarly, the mean glycohemoglobin of the subjects with false positive results, 12.8 +/- 2.4%, was not significantly different than that of the subjects with normal responses, 12.9 +/- 2.5%. There was no correlation between plasma cortisol after dexamethasone and glycohemoglobin (r = 0.05), and only a weak correlation with the mean serum glucose (r = 0.21). We conclude that the 1 mg overnight DST is a valid screening test for Cushing's syndrome in patients with diabetes, regardless of glycemic control.     

Evaluation of endocrine tests. B: screening for hypercortisolism

BACKGROUND: While reference values for 24-hour free urinary cortisol excretion and the overnight 1 mg dexa-methasone-suppression test in the healthy population are available, cut-off values in patients clinically suspected of Cushing's syndrome have to be established. METHODS: This was a prospective follow-up study in one academic centre of 144 patients with clinical suspicion of Cushing's syndrome (group A) and 50 patients with adrenal incidentaloma (group B) who were referred for putative hypercortisolism between 1 January 1993 and 1 January 2003. The 24-hour urinary free cortisol and post-dexamethasone plasma cortisol were measured. Accurate diagnosis of (absence of) Cushing's syndrome was confirmed by histopathological data and long-term follow-up. Based on the data obtained in group A, sensitivity, specificity and receiver operating characteristic (ROC) curves were calculated. RESULTS: Complete follow-up was obtained in 86%, and partial follow-up was obtained in 8% of patients. Median follow-up was 36 (1 to 122) months. In group A, 17 patients were found to have Cushing's syndrome. In this group median 24-hour urinary free cortisol was 77 (<5 to 51458) mmol/24 hours and median post-dexamethasone plasma cortisol was <50 (<50 to 4900) nmol/l. Area under the ROC curve was 0.958 for 24-hour urinary free cortisol and 0.985 for post-dexamethasone plasma cortisol. Optimal cut-off values were 180 nmol/24 hours (sensitivity 94%, specificity 94%) and 95 nmol/l (sensitivity 100%, specificity 94%) respectively. CONCLUSION: We established cut-off values for 24-hour free urinary cortisol excretion (180 nmol/24 hours) and for post-dexamethasone plasma cortisol (95 nmol/l) in the evaluation of patients referred for hypercortisolism.     

Recurrent ACTH-independent Cushing's syndrome in multiple pregnancies and its treatment with metyrapone

A 17-year-old primigravid woman presented with Cushing's syndrome. Typical clinical symptoms and signs developed at the beginning of pregnancy. By week 17 of gestation, plasma cortisol diurnal rhythm was absent and there was a paradoxical increase in plasma cortisol after a 1-mg dexamethasone overnight suppression test. Basal urinary free cortisol was 10 times above the upper limit (in pregnancy) and ACTH levels were suppressed. The diagnosis of ACTH--independent Cushing's syndrome was established. MRI scans revealed normal adrenal and pituitary glands. To control hypercortisolism, the patient was treated with metyrapone. At 34 weeks of gestation, the patient developed preeclampsia and underwent caesarean section. A female infant weighing 1070 g was delivered. No apparent metyrapone-induced teratogenic effects were observed. Cushing's syndrome in the patient resolved within three weeks of delivery. No corticosteroid replacement therapy either for child or mother was needed. Eight months after delivery the patient became pregnant again and rapidly developed Cushing's syndrome with typical clinical symptoms and signs and laboratory results (urinary free cortisol 6464 nmol/24 h). This second pregnancy was unwanted and terminated by artificial abortion that was followed by rapid resolution of hypercortisolism. A third pregnancy, 12 months after delivery was also accompanied by the rapid development of hypercortisolism which recovered after artificial termination. The mechanisms by which pregnancy-induced Cushing's syndrome occurred in this patient are unclear. Aberrant responsiveness or hyperresponsiveness of adrenocortical cells to a non-ACTH and non-CRH substance produced in excess in pregnancy should be considered. Metyrapone suppression of hypercortisolism currently represents the best treatment for these rare cases.     

Effects of the opiate agonist loperamide on pituitary-adrenal function in patients with suspected hypercortisolism

In the present work the possible use of loperamide, an opiate agonist, in the dynamic evaluation of patients with suspected hypercortisolism was investigated. The effects of loperamide on plasma ACTH and cortisol levels were evaluated in normal subjects and in 58 patients with suspected Cushing's syndrome. The results were compared to those obtained after the overnight dexamethasone suppression test. In normal subjects plasma ACTH and cortisol levels were significantly (p less than 0.005) suppressed by both loperamide (16 mg po) and dexamethasone (1 mg po). In 17 patients, in whom the diagnosis of Cushing's syndrome was confirmed by subsequent investigations, neither loperamide or dexamethasone inhibited cortisol (from a baseline of 606 +/- 55 nmol/L) to a nadir of 502 +/- 43 nmol/L and 539 +/- 50 nmol/L, respectively) and ACTH concentration (from a basal level of 70.1 +/- 11.8 pg/ml to a nadir of 46.0 +/- 8.6 pg/ml and 54.3 +/- 7.5 pg/ml, respectively). In 34 patients, in whom the suspect of hypercortisolism was ruled out, either loperamide or dexamethasone suppressed the pituitary-adrenal axis: cortisol and ACTH levels significantly fell from 417 +/- 24 nmol/L and 28.3 +/- 3.5 pg/ml to 60 +/- 6 nmol/L and 14.4 +/- 1.4 pg/ml after loperamide and to 26 +/- 4 nmol and 16.4 +/- 1.7 pg/ml after dexamethasone. In 7 patients discordant responses were observed. In 3 patients treated with antiepileptic drugs ACTH and cortisol levels were inhibited by loperamide, but not by dexamethasone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Salivary cortisol measurement--a reliable method for the diagnosis of Cushing's syndrome.

The measurement of cortisol in saliva is becoming more widely accepted as a screening test for the diagnosis of hypercortisolism. Since 1986, cortisol measurement in saliva has been continuously used in our department. In this study we compared salivary cortisol profiles from proven Cushing's disease patients with profiles from healthy subjects and obese children. The purpose was to evaluate the predictive value of the method for the diagnosis of hypercortisolism and to define cut-off levels to exclude or identify hypercortisolism. Cortisol in saliva was measured in 150 Cushing's disease patients (30 children, 120 adults, ranging from age 4-70), 100 healthy subjects (55 children, 45 adults, ranging from age 6-60), and 31 children (age 7-15) with an age-related body-mass-index above the 90th percentile. Generally, five saliva samples were taken over the day at 6:00-8:00 a.m., 11:00-12:00 a.m., 4:00-6:00 p.m., 7:00-8:00 p.m., and 10:00 p.m. The samples were measured using a radioimmuno-assay (INCSTAR Corporation, Stillwater, Minnesota, USA). For healthy subjects, morning levels of cortisol in saliva between 3-19 microg/l were found. These levels dropped to levels in between <1-11 microg/l at 11:00-12:00 a.m., <1-6 microg/l at 4:00-6:00 p.m., <1-4.5 microg/l at 7:00-8:00 p.m., and <1-2.9 microg/l at 10:00 p.m. The measured values showed a correlation with age, height, and weight. In Cushing's disease patients, the circadian salivary cortisol rhythm was missing, compared to healthy subjects. There was no significant difference in salivary cortisol levels or circadian rhythm between healthy or obese children. We found a high sensitivity for the detection of hypercortisolism at the 10:00 p.m. salivary cortisol measurement. The following, age dependent cut-off levels for salivary cortisol at 10:00 p.m. were calculated for the exclusion of hypercortisolism. Age 6-10: 1.0 microg/l (specificity 100%, sensitivity 87.5%); age 11-15: 1.7 microg/l (specificity 100%, sensitivity 100%); age 16-20: 1.6 microg/l (specificity 100%, sensitivity 76.2%); age 21-60: 1.6 microg/l (specificity 100%, sensitivity 90.9%) [corrected] For the proof of Cushing's syndrome, the following age-dependent cut-off levels at 10:00 p.m. were found: age 6-10: 1.9 microg/l (specificity 100%, sensitivity 80%); age 11-15: 1.7 microg/l (specificity 100%, sensitivity 100%); age 16-20: 2.5 microg/l (specificity 100%, sensitivity 84.2%); age 21-60: 1.9 microg/l (specificity 100%, sensitivity 97.6 %) [corrected] The cortisol assessment in saliva is a sensitive and reliable method to discriminate normocortisolemic from hypercortisolemic patients. From our view, the major advantages of this method are the reliability, non-invasiveness, and use in ambulatory patients.     

Discriminatory value of the low-dose dexamethasone suppression test in establishing the diagnosis and differential diagnosis of Cushing's syndrome

Cushing's syndrome requires a screening test of high sensitivity, followed by biochemical evaluation of the source of the tumor when the cause is ACTH dependent. The high-dose dexamethasone suppression test is still in common use as an aid in differential diagnosis, although its value has been queried. We have routinely used the low-dose dexamethasone suppression test for many years in the diagnosis of Cushing's syndrome but noticed that patients with pituitary-dependent Cushing's syndrome or Cushing's disease, usually showed some degree of suppression of their serum cortisol, compared to those with the ectopic ACTH syndrome. We therefore analyzed retrospectively the serum cortisol responses during the low-dose dexamethasone suppression test and the high-dose dexamethasone suppression test in 245 patients with ACTH-dependent Cushing's syndrome and compared the diagnostic utility of each test either alone or in combination with a standard test using CRH. Evaluation of the serum cortisol response at 24 and 48 h during the low-dose dexamethasone suppression test correctly identified 98% of patients with ACTH-dependent Cushing's syndrome and distinguished between pituitary and ectopic causes with a sensitivity of 82% and a specificity of 79%. In the same patients, the serum cortisol response to the high-dose dexamethasone suppression test had a slightly higher sensitivity (91%) and specificity (80%). However, the combined criteria of a more than 30% suppression of serum cortisol during the low-dose dexamethasone suppression test and/or a more than 20% increase in the CRH test had a significantly higher sensitivity (97%) and specificity (94%) than either the high-dose dexamethasone or the CRH tests alone in the differential diagnosis of ACTH-dependent Cushing's syndrome. It produced equivalent information to that when high-dose and CRH test results were combined. We therefore conclude that in our patient series, the serum cortisol response during the low-dose dexamethasone suppression test is highly sensitive in diagnosing Cushing's syndrome and, combined with the results of the serum cortisol response to the CRH test, offered a safe and cost-effective test in the differential diagnosis of ACTH-dependent Cushing's syndrome. There does not appear to be any necessity for retaining the high-dose dexamethasone suppression test in this diagnostic work-up.     

Cushing's syndrome: a review of diagnostic tests.

This review presents an analysis and interpretation of the published experimental data that form the basis for laboratory tests commonly used for screening, definitive diagnosis, and differential diagnosis in Cushing's syndrome. The single-dose overnight dexamethasone suppression test is excellent for screening outpatients since this test has a very low incidence of false-negative results (1.9% of 154 patients with Cushing's syndrome). The definitive diagnosis of Cushing's syndrome is best established by combining basal state measurements of the daily urine-free cortisol excretion and late evening plasma cortisol levels with the 2-mg low-dose dexamethasone suppression test. The etiology of Cushing's syndrome is best determined by combining measurements of basal state plasma adrenocorticotropin (ACTH) levels with the 8-mg high-dose dexamethasone suppression test. Under certain conditions, the basal state daily urine excretion of 17-hydroxycorticosteroids and 17-ketogenic steroids, the insulin tolerance test, and the metyrapone test may be useful in the definitive or differential diagnosis of Cushing's syndrome.     

Diagnosis and differential diagnosis of Cushing's syndrome.

The clinical recognition of Cushing's syndrome and its biochemical confirmation is a challenging problem. The best diagnostic approach to patients with suspected Cushing's syndrome is still evolving. The traditional diagnostic approach of urine free cortisol and low-dose dexamethasone suppression testing may be inadequate when the degree of hypercortisolism is mild. Late-night salivary cortisol determinations may evolve as the simplest means of screening patients for suspected hypercortisolism. Repeated measurements of cortisol secretion (urine free cortisol or late-night salivary cortisol) over an extended period of time may be necessary to provide diagnostic certainty. The dexamethasone-CRH test is a reasonable approach in patients with equivocal data. The introduction of reliable, sensitive, and specific plasma ACTH measurements, the use of IPSS for ACTH with CRH stimulation, and the improved techniques of pituitary and adrenal imaging have made the differential diagnosis of Cushing's syndrome relatively straightforward (see Fig. 2). Clinicians who have never missed the diagnosis of Cushing's syndrome or have never been fooled by attempting to establish its cause should refer their patients with suspected hypercortisolism to someone who has.     

EVALUATION OF STEROID LABORATORY TESTS AND ADRENAL GLAND IMAGING WITH RADIOCHOLESTEROL IN THE AETIOLOGICAL DIAGNOSIS OF CUSHING''S SYNDROME

Basal values of the urinary excretion of 17-oxogenic steroids and serum levels of cortisol were not satisfactory in the differentiation of 'suspected' subjects from patients with true Cushing's syndrome. With an RIA method for serum cortisol determination, the overnight dexamethasone suppression test provided the most reliable single test in establishing adrenocortical hyperfunction. Thirty-five normal subjects, fifty-nine obese patients, thirteen 'suspected' patients, and thirteen patients with disease states other than Cushing's syndrome had suppressed values below 4.0 microgram/100 ml. None of the ten patients with Cushing's syndrome had a cortisol concentration less than 16.3 microgram/100 ml. Adrenal gland scintigraphy after radiocholesterol injection is a more valuable tool than the metyrapone test and the high-dose dexamethasone suppression test in the localization and differential diagnosis of adrenocortical lesions causing Cushing's syndrome. It obviates the need for angiographic procedure in the localization of adenomas. It is a reliable technique for identifying functioning adrenal remnants. We therefore propose a schedule for studying patients with suspected adrenocortical hyperfunction.     

Midnight salivary cortisol for the initial diagnosis of Cushing's syndrome of various causes

We assessed the value of midnight salivary cortisol for the initial diagnosis of Cushing's syndrome. Sixty-three patients with various causes of Cushing's syndrome (37 with Cushing's disease, 17 with adrenal Cushing's syndrome, and nine with ectopic ACTH syndrome) and 54 control subjects with simple obesity were studied. All patients with Cushing's syndrome excreted more than 90 microg urinary free cortisol (UFC)/d (248 nmol/d), and all controls excreted less than 90 microg/d UFC. All patients with Cushing's syndrome had a midnight salivary cortisol concentration above 2.0 ng/ml (5.52 nmol/liter), whereas only three controls did so [2.0 ng/ml (5.52 nmol/liter); 2.05 ng/ml (5.66 nmol/liter); and 3.6 ng/ml (9.96 nmol/liter)]. This cut-off provides a sensitivity of 100% and a specificity of 96%. In patients with Cushing's syndrome, midnight salivary cortisol concentrations were correlated with UFC collected over the same period of time (0800-0800 h). Salivary cortisol measurements taken every 4 h showed a typical lack of circadian variation. The daily measurement of midnight salivary cortisol concentrations for 2 wk or more in five other out-patients (with obvious Cushing's disease, subclinical adrenal Cushing's syndrome, suspected Cushing's syndrome, pituitary incidentaloma, and prolactinoma) demonstrated the clinical utility of this factor. Measuring midnight salivary cortisol is an easy and noninvasive means of diagnosing hypercortisolism. Its diagnostic accuracy is identical to, if not better than, that of previously described gold standards.     

The ovine corticotropin-releasing hormone stimulation test and the dexamethasone suppression test in the differential diagnosis of Cushing's syndrome

We gave a standard dexamethasone suppression test and an ovine corticotropin-releasing hormone (CRH) stimulation test to 41 patients with adrenocorticotrophic hormone (ACTH)-dependent hypercortisolism to determine the efficacy of each test in the differential diagnosis of Cushing's syndrome. Twenty-nine of thirty-three patients with Cushing's disease and 0 of 8 patients with ectopic secretion of ACTH responded to the ovine CRH test with increased levels of cortisol. When a cortisol response was judged as positive for Cushing's disease, the CRH test had a diagnostic sensitivity, specificity, and accuracy of 88%, 100%, and 90%, respectively. Twenty-nine patients with Cushing's disease and 1 patient with ectopic secretion of ACTH responded to the dexamethasone suppression test. A combined-test strategy requiring negative results from both tests to exclude a diagnosis of Cushing's disease yielded superior sensitivity (100%) and diagnostic accuracy (98%). Thus, the ovine CRH test works as well as the standard dexamethasone suppression test in discriminating between Cushing's disease and ectopic ACTH secretion. The diagnostic power of each test is enhanced when the two tests are combined.     

THE OVERNIGHT DEXAMETHASONE TEST IS A WORTHWHILE SCREENING PROCEDURE

The overnight low-dose dexamethasone test is a convenient screening procedure for Cushing's syndrome. Claims that the test is associated with a high incidence of 'false positives', rendering it of little value particularly in obese and hospital in-patients, have been investigated in the present study. The data from 100 consecutive subjects undergoing overnight low-dose dexamethasone tests to examine for the possibility of Cushing's syndrome, were reviewed. Cushing's syndrome was identified in four patients, normal suppression of cortisol values occurred in 84 patients and 12 patients exhibited false positive results. Differences in body weights, body mass indices or in-patient status did not distinguish between those subjects with normal suppression of plasma cortisol and those subjects who yielded false positive results. These data indicate that the simple overnight dexamethasone test substituted for the more cumbersome traditional 48-h dexamethasone test in 84 of 96 patients who did not have Cushing's syndrome. Thus the overnight test provides a useful screening procedure but a small percentage of patients, approximately 12.5%, will require additional procedures to exclude Cushing's syndrome.     

Subclinical Cushing's syndrome.

Classic Cushing's syndrome is a rare disease with an estimated incidence of 1 case per 100,000 persons. With routine use of imaging techniques such as ultrasound and CT, adrenal masses are being detected with increased frequency. A substantial percentage of these incidentalomas are hormonally active, with 5% to 20% of the tumors producing glucocorticoids. Autonomous glucocorticoid production without specific signs and symptoms of Cushing's syndrome is termed subclinical Cushing's syndrome. With an estimated prevalence of 79 cases per 100,000 persons, subclinical Cushing's syndrome is much more common than classic Cushing's syndrome. Depending on the amounts of glucocorticoids secreted by the tumor, the clinical spectrum ranges from slightly attenuated diurnal cortisol rhythm to complete atrophy of the contralateral adrenal gland with lasting adrenal insufficiency after unilateral adrenalectomy. Patients with subclinical Cushing's syndrome lack the classical stigmata of hypercortisolism but have a high prevalence of obesity, hypertension, and type 2 diabetes. All patients with incidentally detected adrenal masses scheduled for surgery must undergo testing for subclinical Cushing's syndrome to avoid postoperative adrenal crisis. The best screening test to uncover autonomous cortisol secretion is the short dexamethasone suppression test. Because the adrenal origin of a pathologic cortisol secretion is anticipated, the author prefers a higher dexamethasone dose (3 mg instead of 1 mg) to reduce false-positive results. A suppressed serum cortisol level of less than 3 micrograms/dL (80 nmol/L) after dexamethasone excludes significant cortisol secretion by the tumor. A serum cortisol level greater than 3 micrograms/dL requires further investigation, including confirmation by high-dose dexamethasone (8 mg) suppression testing, a CRH test, and analysis of diurnal rhythm. Determination of urinary free cortisol is less useful because increased values are a late finding usually associated with emerging clinical signs of Cushing's syndrome. Patients with suppressed plasma ACTH in response to CRH generally have adrenal insufficiency after surgery and require adequate perioperative and postoperative substitution therapy. Whether patients with subclinical Cushing's syndrome should undergo adrenalectomy is a matter of debate. The author performs surgery in young patients (< 50 years), in patients with suppressed plasma ACTH, and in patients with a recent history of weight gain, substantial obesity, arterial hypertension, diabetes mellitus, and osteopenia. In completely asymptomatic patients with normal plasma ACTH concentrations and in patients older than 75 years, the author recommends a nonsurgical approach. A large prospective randomized study is necessary to evaluate the benefits of surgery versus conservative treatment in patients with subclinical Cushing's syndrome.     

Out-patient screening for Cushing's syndrome: the sensitivity of the combination of circadian rhythm and overnight dexamethasone suppression salivary cortisol tests

Screening tests have been used to support a biochemical diagnosis of Cushing's syndrome (CS). Measurements of salivary cortisol offer facilities for studying out-patients. This study assessed salivary cortisol in screening for CS by evaluating hypercortisolism based on circadian rhythm and the overnight 1-mg dexamethasone (DEX) suppression test for out-patients. We evaluated 33 patients with CS. Thirty normal volunteers and 18 obese patients were used as controls. Salivary cortisol (nanograms per dL) levels (mean +/- SEM) were 596 +/- 44, 528 +/- 104, and 1205 +/- 118 (0900 h); 213 +/- 27, 325 +/- 76, and 778 +/- 74 (1700 h); and 95 +/- 8, 133 +/- 26, and 914 +/- 94 (2300 h) in normal controls, obese subjects, and CS patients, respectively. After the overnight 1-mg DEX test, they were 64 +/- 1.1, 107 +/- 25, and 1048 +/- 129, respectively. In the present series, a single out-patient 0900, 1700, and 2300 h measurement and an overnight 1-mg DEX salivary cortisol level above the 90th percentile of the control or obese group values had sensitivities of 65.6%, 81.8%, 100%, and 100% or 78.1%, 57.6%, 93.3%, and 91.4%, respectively. The sensitivity improved (100%) in response to the combination of 2300 h and overnight 1-mg DEX salivary cortisol suppression tests to differentiate between obese and CS subjects. Our data indicate that nighttime sample and overnight 1-mg DEX suppression salivary cortisol tests are sensitive markers for the diagnosis of CS. In addition, the combination of the two tests improves the ability to differentiate between obese and CS patients and may be useful for out-patient screening.     

Clinical experience with a simple screening test for Cushing's syndrome combining the determination of plasma cortisol circadian rhythm with the overnight dexamethasone suppression test

In 17 normal subjects and 126 patients with various endocrine disorders, including 13 patients with Cushing's syndrome, plasma levels of fluorogenic corticosteroid were measured at 9 AM and midnight, and again at 9 AM the following morning, after the patient had received 1 mg of dexamethasone by mouth immediately after the midnight sampling. Basal morning levels of plasma corticosteroids were of little diagnostic value in differentiating between Cushing's syndrome and non-Cushing's states because of the wide overlap of values observed. At midnight the overlap almost completely disappeared. After overnight suppression, only one patient with a mild form of Cushing's disease had normal (false-negative) results in two of four instances. There were virtually no false-positive results, except for two patients with anorexia nervosa showing minor abnormalities of the test. The results were in general agreement with those of the classic Liddle test. However, one patient with Cushing's disease had repeatedly abnormal responses to overnight suppression and normal responses to the Liddle test. When the inhibitory tests gave equivocal results in the differential diagnosis between exogenous obesity and Cushing's disease due to adrenal hyperplasia, the response of plasma corticosteroids to hypoglycemia, normal in obesity and absent in Cushing's disease, proved to be an excellent ancillary test in differentiating between the two conditions.