Single Intravenous Bolus of Dexamethasone for the Differential Diagnosis of Cushing’s Syndrome
Shmuel Shilo1 and Ariel Rosler2
Endocrine Service, Shaare Zedek Medical Center1 and Department of Endocrinology and Metabolism, Hebrew University-Hadassah Medical Center2. Jerusalem, Israel
ABSTRACT
We developed a 24 hour intravenous dexamethasone suppression test for the differential diagnosis of Cushing’s syndrome. Basal ACTH and cortisol levels were measured at 8 and 9 AM; a bolus of 8 mg dexamethasone phosphate (in children 5 mg/m2) was administered intravenously, and cortisol levels were measured hourly until 3 PM, then every 2 hours until midnight, and the next morning at 8 and 9 AM. We studied 13 patients with an ACTH-secreting pituitary adenoma, four with an autonomous adrenal adenoma, a 10 year-old girl with primary adrenocortical nodular dysplasia, one male with an ACTH-secreting medullary carcinoma of the thyroid, and one male with an ACTH-secreting non-small cell carcinoma of the lung, and compared their results to those obtained in 8 lean and 12 obese normal individuals (controls). The clinical diagnosis was first ascertained by the response to the oral administration of dexamethasone in low and high doses (standard Liddle test), then by the intravenous dexamethasone suppression test, and finally confirmed surgically. Although both controls and patients with an ACTH- secreting pituitary adenoma significantly suppressed their cortisol levels within hours after the injection (50% reduction of basal value at 2 hours, and 75% at 4 hours, p<0.0001), levels remained suppressed the next morning only in the controls, while in the patients they returned to basal values. No suppression was observed in
any of the patients with an adrenal adenoma and the child with primary adrenocortical nodular dysplasia (whose ACTH levels were low), or in the patients with ectopic ACTH secretion tumors (whose ACTH levels were high). This test is easy to perform on an ambulatory basis, and may distinguish patients with hypercortisolism of different etiologies from normal and obese individuals, within a short period of time. If studies in a larger population will render similar results, the test may be simplified further by reducing the frequency of blood sampling.
INTRODUCTION
Oral administration of dexamethasone in low and high doses, as described by Liddle in 1960 /1/, is still being used for the differential diagnosis of patients with hypercortisolism /2/. Low doses (0.5 mg every six hours, for 48 hours) will suppress ACTH and cortisol secretion in normal individuals only, while high doses (2 and 4 mg every six hours, for 48 hours) will partially suppress these parameters in patients with an ACTH-secreting pituitary adenoma. In other types of Cushing’s syndrome ACTH and cortisol are usually non- suppressible. Although the results may be reliable in most patients, the test as originally designed has major disadvantages. It is long, requires good compliance in taking dexamethasone regularly, adequate gut absorption, and proper urinary collections. To avoid some of these problems Tyrrel et al. designed in 1986 /3/ an overnight oral (high dose) dexamethasone suppression test. However, this test did not always differentiate patients with an ACTH-secreting pituitary adenoma and other forms of Cushing’s syndrome, from normal individuals.
Reprint address: Ariel Rösler, M.D. Department of Endocrinology and Metabolism Hebrew University-Hadassah Medical Center P.O.B. 12000, Jerusalem 91120, Israel
VOLUME 8, NO. 1, 1995
Intravenous dexamethasone suppression tests have been available since 1965 /4-10/. Most of them consist of a fixed dose of dexamethasone (1 to 1.5 mg/hour) infused during 3 to 7 hours, and cortisol levels are measured basally and several hours to a day later. The degree of suppression is used to differentiate normal individuals from patients with ACTH-secreting pituitary adenoma and other forms of Cushing’s syndrome. These tests are, however, tedious to perform, and their results have not been always reliable.
We developed a simplified test, in which a single bolus of 8 mg dexamethasone phosphate is administered intravenously. This test may accurately differentiate normal individuals from patients with hypercortisolism of different etiologies.
MATERIALS AND METHODS
Subjects
Twelve females and one male (mean age 42.2 ± 13.2 years, range 16 to 67 years) with an ACTH- secreting pituitary adenoma, three females and one male with an autonomous adrenal adenoma (aged 31, 46, 43 and 34 years, respectively), a 10 year-old girl with primary adrenocortical nodular dysplasia /11/, a 19 year-old boy with an ACTH-secreting medullary carcinoma of the thyroid, and a 44 year- old male with an ACTH-secreting non-small cell carcinoma of the lung were included in the study. Seventeen normal females and three males (mean age 29.3 ± 13.0 years, range 16 to 63 years), referred for the evaluation of possible hyper- cortisolism, served as controls. Twelve of them were obese (20% or more above the ideal body weight). In the control group hypercortisolism was ruled out on clinical grounds, as well as by the suppression of plasma cortisol to less than 85 nmol/l in response to 1 mg dexamethasone, administered orally at midnight /12/. The patients’ group was initially studied by the standard Liddle’s test (data not shown) /1/, and afterwards by the single bolus intravenous dexamethasone test, as described below. All patients were studied while inpatients. In all instances the clinical diagnosis was confirmed surgically. Except for one patient, who received replacement of L-thyroxine for primary hypo-
thyroidism, none of the others was taking any medication. The study was approved by an Institutional Committee for Human Rights (Hebrew University-Hadassah Medical Center), in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from all subjects.
Protocol
After an overnight fast, an intravenous cannula with heparin lock was introduced into an antecubital vein. Blood specimens were drawn at 8 and 9 AM, for basal values of ACTH and cortisol. Thereafter, a single 8 mg bolus of dexamethasone phosphate was injected intravenously. In children the dose of dexamethasone was calculated on basis of body surface area, 5 mg/m2. Blood samples for cortisol and dexamethasone measurements were drawn at one hour intervals until 3 PM, then every two hours until midnight, and the following day at 8 and 9 AM. No adverse side effects were observed during or after the test.
Methods
Plasma ACTH was quantified using a dual- antibody immunoradiometric assay (Allegro HS- ACTH; Nichols Institute, Los Angeles, California) /13/ Plasma cortisol was determined by a sensitive and specific radioimmunologic method described previously /14/, and dexamethasone was measured by a modification of the assay described by Meikle et al. /15/.
Statistical analysis was performed by Student’s unpaired t-test.
RESULTS
Table 1 shows the cortisol concentrations in all patients with Cushing’s syndrome before and during 24 hours after the intravenous bolus of dexametha- sone, compared to the values in the control population. The basal (mean ± SD) cortisol concentrations in patients with an ACTH-secreting pituitary adenoma were 652 ± 240 nmol/l, and in controls 355 ± 102 nmol/l (p < 0.0001). The basal ACTH levels in these patients were 14 + 6 pmol/l, range 5 to 36 (individual data not shown), while in
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| Time in hours | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sex/Age | Diagnosis | -1 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 9 | 11 | 13 | 15 | 23 | 24 |
| F/42 | P | 607 | 472 | 389 | 270 | 176 | 108 | 94 | 88 | 61 | 83 | 171 | 315 | 251 | 502 | 328 |
| F/35 | P | 1363 | 1084 | 1035 | 850 | 513 | 574 | 762 | 819 | 993 | 877 | 1004 | 1087 | 1137 | 996 | |
| F/48 | P | 582 | 544 | 441 | 276 | 229 | 210 | 127 | 119 | 135 | 119 | 226 | 221 | 461 | 557 | 761 |
| F/16 | P | 312 | 582 | 499 | 135 | 168 | 179 | 113 | 121 | 66 | 58 | 52 | 97 | 546 | 766 | |
| F/43 | P | 728 | 679 | 428 | 232 | 154 | 132 | 102 | 80 | 77 | 75 | 146 | 132 | 141 | 425 | 370 |
| F/42 | P | 519 | 709 | 610 | 422 | 281 | 201 | 144 | 135 | 146 | 102 | 226 | 364 | 400 | ||
| F/42 | P | 350 | 430 | 353 | 240 | 182 | 110 | 168 | 52 | 35 | 33 | 276 | 276 | 226 | 460 | 439 |
| F/43 | P | 621 | 624 | 706 | 491 | 433 | 232 | 264 | 157 | 254 | 552 | 613 | 712 | 991 | 764 | |
| F/68 | P | 621 | 924 | 475 | 334 | 234 | 190 | 160 | 97 | 99 | 113 | 105 | 91 | 86 | 419 | 392 |
| M/29 | P | 811 | 640 | 605 | 439 | 392 | 185 | 121 | 165 | 72 | 433 | 533 | 637 | 529 | 640 | 620 |
| F/52 | P | 400 | 530 | 524 | 601 | 246 | 212 | 124 | 185 | 154 | 209 | 163 | 298 | 138 | 328 | 417 |
| F/27 | P | 1144 | 972 | 579 | 510 | 312 | 210 | 168 | 47 | 41 | 444 | 499 | 784 | 880 | 974 | 1068 |
| F/67 | P | 602 | 530 | 524 | 246 | 212 | 174 | 185 | 155 | 210 | 163 | 248 | 138 | 328 | 417 | |
| Mecan | (N=13) | 608 | 692 | 555 | 415 | 300 | 205 | 177 | 186 | 161 | 244 | 301 | 367 | 382 | 590 | 591 |
| ± 6D | 224 | 257 | 187 | 238 | 185 | 105 | 125 | 202 | 212 | 261 | 241 | 298 | 328 | 271 | 248 | |
| F/31 | A | 560 | 544 | 563 | 535 | 519 | 571 | 019 | 557 | 579 | 447 | 535 | 690 | 660 | 651 | 499 |
| F/46 | A | 624 | 486 | 353 | 348 | 406 | 356 | 447 | 433 | 425 | 472 | 496 | ||||
| F/43 | A | 425 | 450 | 447 | 458 | 417 | 444 | 466 | 480 | 458 | 499 | 488 | 540 | 413 | 596 | 864 |
| M/34 | A | 952 | 1022 | 817 | 1380 | 1092 | 1259 | 1129 | 992 | 861 | 110G | 1200 | 1048 | 843 | 679 | |
| F/10 | PAND | 471 | 495 | 554 | 487 | 442 | 473 | 479 | 552 | 597 | 534 | 538 | 310 | |||
| M/19 | E-1 | 855 | 918 | 913 | 665 | 827 | 1029 | 1007 | 886 | 842 | 847 | 875 | 872 | 871 | 1145 | 1247 |
| M/44 | E-2 | 738 | 811 | 787 | 859 | 789 | 721 | 683 | 794 | 698 | 1010 | 1380 | 1610 | |||
| Mean | (N=7) | 661 | 675 | 680 | 676 | 633 | 700 | 720 | 643 | 654 | 652 | 756 | 788 | 648 | 803 | 729 |
| ± 8D | 196 | 235 | 183 | 350 | 273 | 326 | 321 | 226 | 176 | 249 | 318 | 220 | 229 | 346 | 329 | |
| Controls Mean | (N=20) | 379 | 331 | 251 | 153 | 103 | 72 | 59 | 47 | 44 | 37 | 36 | 32 | 32 | 46 | 37 |
| 1 80 | 100 | 104 | 63 | 50 | 39 | 21 | 17 | 178 | 22 | 14 | 13 | 10 | 10 | 30 | 20 | |
P: ACTH-secreting pituitary adenoma; A: autonomous adrenal adenoma; PAND: primary adrenocortical nodular dysplasia; E-1: ectopic ACTH-secreting medullary carcinoma of thyroid; E-2: ectopic ACTH-secreting non-small cell carcinoma of lung.
normal subjects the values ranged between 4 and 18 pmol/l. The integrated basal (mean + SD) cortisol levels in the patients with an adrenal adenoma (N=4), primary adrenocortical nodular dysplasia, and the two with an ectopic ACTH-secreting tumor were 667 ± 209 nmol/l (p < 0.0001, compared to the controls), while their ACTH levels were less than 4, 5.6, and 172 and 82 pmol/l, respectively. After the dexamethasone injection plasma cortisol rapidly decreased to very low levels in the controls and in all patients with an ACTH-secreting pituitary adenoma. However, only in the control population did the cortisol levels remain suppressed the next morning, whereas in all patients with Cushing’s disease the values returned to the basal levels of the previous day (p < 0.0001). On the other hand, none
of the patients with an adrenal adenoma, primary adrenocortical nodular dysplasia, or ectopic ACTH- secreting tumor suppressed their cortisol levels during the entire period of the test.
Figure I shows the percentage decrease of the integrated cortisol concentrations (mean ± SE) in all tested patients with hypercortisolism, compared to the control values. The pattern in the patients with an ACTH-secreting pituitary adenoma and controls is similar during the first 5 to 7 hours, with a 50% reduction in cortisol levels after 2 hours, and 75% after 4 hours. Thereafter cortisol levels remained suppressed only in the controls, but in the patients with an ACTH-secreting pituitary adenoma returned progressively to basal levels by the next morning (p< 0.0001). In all other patients with Cushing’s
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syndrome cortisol levels did not suppress (p <0.0001), and compared to controls, were significantly higher during the 24 hours of the test.
One hour after the injection plasma dexa- methasone levels ranged between 401.4 nmol/l to 1194.7 nmol/1 (208 ng/dl to 619 ng/dl) in the control group, and between 422.7 nmol/l to 1088.5 nmol/1 (219 ng/dl to 564 ng/dl) in the patients with Cushing’s disease and adrenal adenoma. Figure 2 shows the dexamethasone disappearance curve in these three groups, using the mean concentrations measured at the end of the first hour as 100% /16/. In controls and patients with an ACTH-secreting pituitary adenoma the dexamethasone levels decreased promptly after the injection, following a slower but similar pattern than cortisol. A 50% decrease in dexamethasone concentrations was observed after approximately 6-1/4 hours, and a 75% decrease after 13-1/2 hours. In patients with an adrenal tumor, no significant decrease was noted during the first 4 hours. In this group, a 50% decrease occurred approximately 10 hours after the intravenous administration of dexamethasone.
Figure 3 shows the results of this test in two patients with an ACTH-secreting pituitary adenoma, before and one year after transphenoidal adenomec- tomy. The upper panel illustrates a patient whose surgery was successful. Prior to surgery cortisol levels suppressed promptly following the intravenous administration of dexamethasone, but escaped after 16 hours, returning to basal levels the next morning. One year after transphenoidal adenomectomy the cortisol response to a 8 mg dexamethasone bolus was similar to that in normal controls. On the other hand, the lower panel illustrates another patient with an ACTH-secreting pituitary adenoma who underwent unsuccessful surgery. The abnormal pattern of cortisol suppression was found unchanged after the operation, although the absolute levels were lower than before.
DISCUSSION
Once hypercortisolism is established it is necessary to differentiate normal subjects with high plasma cortisol levels from patients with the various forms of Cushing’s syndrome. The classic Liddle’s
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test /1/ is still being used, in spite of its disadvantages, including 13% false negative results in patients with an ACTH-secreting pituitary adenoma, and 26% false positive results in patients with an ectopic ACTH-secreting tumor /17/. In order to shorten the test, simplified oral and intravenous tests have been developed. In the latter a constant dose of dexamethasone phosphate is infused over several hours, and cortisol levels are measured periodically /4-10/. To further simplify these tests, we chose to administer intravenously a single bolus of 8 mg dexamethasone.
In normal controls and patients with an ACTH- secreting pituitary adenoma cortisol concentrations fell significantly (p < 0.0001) during the first 5 to 7 hours after the injection, the degree of suppression being the same in both groups. However, all patients with the pituitary adenoma subsequently escaped suppression and cortisol levels returned to basal values after 24 hours, whereas these remained suppressed in the controls. Thus, the cortisol response during the first 5 to 7 hours after the injection, together with the next morning levels served to distinguish normal individuals and patients with an ACTH-secreting pituitary adenoma from those with other forms of Cushing’s syndrome (in whom cortisol levels remained unchanged during the whole test period). Measuring basal ACTH levels in parallel helped to further differentiate the patients with an autonomous adrenal tumor from those with an ectopic ACTH-secreting tumor, and helped to diagnose the girl with primary adrenocortical nodular dysplasia, who in addition to low ACTH levels and non-suppressible cortisol levels with dexamethasone, had bilateral adrenal uptake of 1311-19-iodocholesterol /11/. This approach is definitively less difficult and hazardous for the patient than determining plasma ACTH from the inferior petrosal sinuses, as recently suggested /18/. The results of this test in ectopic ACTH- secreting tumors need to be validated further, however, since we examined only two such patients.
Studies in our relatively small population of normal and affected individuals suggest that this test seems to be reliable for the differential diagnosis of Cushing’s syndrome. If studies in a larger series of patients will render similar results, we propose to simplify the test further by reducing the frequency of sampling. This could be done, for instance, by obtaining five samples, before, and 2, 4, 6, and 24 h after the injection of dexamethasone. Obviously once the biochemical diagnosis is established localization studies are necessary. We did not have the opportunity to study any patient with a corticotrophin-releasing hormone producing tumor, so that their response to this test is still unknown.
The metabolic clearance rate of dexamethasone was similar in controls and patients with an ACTH- secreting pituitary adenoma. The patients with an adrenal adenoma experienced a delay in the
clearance rate during the first 4 hours. Decreased clearance of dexamethasone was the cause for the abnormal cortisol suppression with low doses of dexamethasone found in several exceptional patients with an ACTH-secreting pituitary adenoma /16, 19/. In our patients, however, cortisol levels did not suppress in spite of the delay in dexamethasone clearance. Since cortisol and dexamethasone utilize similar metabolic pathway(s) for degradation /16/, it is possible that a competitive mechanism may be operative when cortisol is produced in very large quantities (e.g., in large adrenal tumors), thus delaying the clearance of dexamethasone.
In summary, we developed a simplified intravenous dexamethasone suppression test, which may also be useful in the pediatric population. It does not require urinary collections, does not depend on the patient’s compliance in taking the right doses of dexamethasone on time, and is not affected by gut absorption of the drug. The test may rapidly differentiate normal individuals from patients with Cushing’s syndrome of various etiologies, and in addition seems to be useful for the prediction of success or failure of transphenoidal adenomectomy.
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