the definitive diagnosis of endogenous cushing 's syndrome ( cs ) is a challenge in clinical endocrinology . biochemical confirmation of cs relies upon the measurement of urinary free cortisol ( ufc ) over a 24  h period , low dose dexamethasone suppression test ( lddst ) , and plasma cortisol circadian rhythm assessment [ 1 , 2 ] . biochemical tests for the differential diagnosis of cs include baseline plasma adrenocorticotropic hormone ( acth ) measurement , high - dose dexamethasone suppression test ( hddst ) , and corticotropin - releasing hormone ( crh ) stimulation test [ 35 ] . cs is classified as either acth dependent or acth independent . in caucasians , the most common form of the syndrome is acth dependent ( 8085% ) . cushing 's disease ( cd , excessive secretion of corticotropin by pituitary corticotroph tumors ) , accounts for 6080% of cases in most series [ 3 , 57 ] . acth - independent cs ( 1520% ) results from excessive secretion of cortisol by adrenocortical tumors , classified as either adenoma ( 10% ) or carcinoma ( 8% ) , by primary pigmented nodular adrenocortical disease ( ppnad , 1% ) or by acth - independent bilateral macronodular adrenocortical hyperplasia ( aimah , < 1% ) [ 3 , 68 ] . in this study , we analyzed the clinical characteristics of cs at a medical center in southern taiwan and observed a different population distribution compared to western countries for acth - independent cs and acth - dependent cs . from january 1987 to december 2011 , over a total of 25 years , 84 patients with cs were confirmed by clinical manifestation , plasma and/or urinary biochemical laboratory tests , and surgical pathology . these patients were divided into ( a ) those with acth - independent ( adrenal ) cs , including adrenocortical adenomas and carcinomas , ppnad , and aimah and ( b ) those with acth - dependent cs , including cd and ectopic acth syndrome ( eas ) . patients who were suspected of endogenous cs without surgical intervention were excluded . laboratory tests of hypothalamic - pituitary - adrenal function in cs included measurement of baseline morning ( 0800  h to 0900  h ) and afternoon ( 1600  h to 2200  h ) plasma cortisol levels , baseline 24  h ufc , loss of plasma cortisol circadian rhythm ( i.e. , baseline afternoon plasma cortisol level greater than 7.5  g / dl and greater than 50% of baseline morning plasma cortisol level ) , nonsuppression of morning 0800  h plasma cortisol level ( i.e. , greater than 5  g / dl ) after administration of 1  mg dexamethasone orally at 2300  h ( overnight low - dose dexamethasone suppression test , overnight lddst ) , and nonsuppression of 24  h ufc ( > 122  g ) or nonsuppression of morning 0800  h plasma cortisol level ( > 5  g / dl ) 48  h after 0.5  mg dexamethasone administered orally every 6  h for 2 days ( 2-day lddst ) . baseline morning ( 0800  h to 0900  h ) plasma acth levels were also measured . for the 2-day high - dose dexamethasone suppression test ( 2-day hddst , 2  mg dexamethasone administered orally every 6  h for 2 days ) , a plasma cortisol level greater than 50% of the baseline plasma cortisol level or a 24  h ufc level greater than 50% of the baseline 24  h ufc level was indicative of nonsuppression . normal ranges for baseline plasma cortisol are 7.0025.00  g / dl in the morning and 2.009.00  g / dl in the afternoon . baseline 24  h ufc values are 34122  g/24  h. data are expressed as the mean  the standard deviation ( sd ) . statistical analyses were performed using spss 12.0 ( spss , chicago , il , usa ) . the patient distribution and demographic data for 84 patients with cs are presented in table 1 . the mean age of those with acth - independent cs and acth - dependent cs at the time of surgery was 37.5  14.2 and 40.9  16.1 years old , respectively . a larger proportion of our patients had acth - independent cs versus acth - dependent cs ( 75% versus 25% ) . forty - nine of the 84 patients ( 58.3% ) had adrenocortical adenoma , whereas 18 ( 21.4% ) had cd . more women than men had adrenocortical adenoma as well as cd ( table 1 ) . of the 54 patients with unilateral adrenocortical adenoma or carcinoma , the left side ( 33 cases ) one patient with this disease had a tumor 3.3  cm in diameter , as visualized by abdominal computed tomography . after laparoscopic adrenalectomy , the patient developed retroperitoneal and peritoneal seeding . in all patients with cs , baseline morning plasma cortisol levels were often within the normal range ( 60% , 48 out of 80 cases ) but mostly lacked circadian rhythm ( 95.9% of sensitivity ) . the mean baseline plasma cortisol levels of all cs patients at 0800  h and 1600  h2200  h were similar ( 24.6  10.5 versus 22.3  10.0  g / dl ; p = 0.155 ) . the sensitivity of the baseline 24  h ufc values was 88.5% using a cut - off value greater than 122  g/24  h. if the cut - off value for the baseline 24  h ufc was set at greater than 80  g/24  h , the sensitivity increased to 96.2% . the sensitivity of overnight and 2-day lddst using the criteria of plasma cortisol levels greater than 5  g / dl ( indicative of nonsuppression ) was 98.2% and 100% , respectively . the sensitivity of the 2-day lddst using the criterion of a 24  h ufc value greater than 122  g / day ( indicative of nonsuppression ) was 94.4% . five patients in the acth - independent cs group had a baseline 24  h ufc level < 122  g/24  h , with individual values of 32.5 , 88 , 90 , 94 , and 112  g/24  h. one patient with acth - dependent cs also had a very low baseline 24  h ufc level ( 10.7  g/24  h ) . for the 2-day hddst , the sensitivities of 0800  h plasma cortisol levels and 24  h ufc levels using the criteria of more than 50% suppression relative to the baseline values ( i.e. , suppression ) for patients with cd were 44.4% and 85.7% , respectively . the sensitivities of 0800  h plasma cortisol levels and 24  h ufc levels using a cut - off of greater than 50% of baseline levels ( i.e. , nonsuppression ) for patients with adrenal cs were 95.5% and 88.9% , respectively ( table 2 ) . baseline morning plasma acth levels were measured in 62 patients with cs ( table 3 ) . the levels were all below 29  pg / ml in the 43 patients with acth - independent cs . five ( 11.6% ) of those adrenal cs patients had plasma acth levels between 20 and 28.7  pg / ml ( table 3 ) . baseline plasma acth levels were between 37.4 and 328  pg / ml in the 16 patients with cd . three ( 18.8% ) of these patients were found to have levels within the normal range ( 37.4 , 45.8 , and 46.8  pg / ml ) ( table 3 ) . baseline plasma acth levels in three patients with eas ( small cell lung carcinoma , meningioma , and carcinoid tumor ) were 427 , 725 , and 318  pg / ml , respectively . of the sixty - three patients who had adrenal cs , four ( 3 ppnad patients and 1 patient with bilateral adrenocortical adenoma ) received 2 surgical operations each on different dates [ 912 ] , for a total number of 67 operations performed . twenty - four cases with adrenal nodules ( including adenoma , carcinoma , aimah , and ppnad ) were treated with retroperitoneoscopic adrenalectomy . these patients had a mean postsurgical hospitalization stay of 4.3  1.6 days ( mean  sd ) . the other forty - three ( including adenoma , carcinoma , aimah , and ppnad ) were treated with traditional transabdominal adrenalectomy . the difference between the two groups with regard to postsurgical hospital stay was significant ( p value < 0.001 ) . in our study , the incidence of acth - independent cs ( 75% ) was markedly higher than that of acth - dependent cs ( 25% ) , and the incidence of adrenocortical adenoma ( 58.3% ) was markedly higher than that of cd ( 21.4% , table 1 ) . in japan , the incidence of adrenocortical adenoma - induced cs and the incidence of cd were 50.9% and 37.9% , respectively . the distribution of adrenocortical adenoma - induced cs and pituitary cd is different between caucasian ( 7.818.8% for adenoma - induced cs and 6080% for pituitary cd ) and asian ( 50.958.3% and 21.437.9% , resp . ) populations [ 6 , 7 , 14 , 15 ] . the incidence of adrenocortical adenoma and cd by gender distribution is higher amongst females ( table 1 ) . this differential distribution of cs incidence by gender has been noted in other published articles [ 14 , 15 ] . elevated baseline 24  h ufc levels , an absence of normal plasma cortisol circadian rhythm , and loss of normal suppression of cortisol secretion by lddst are all highly sensitive tests for the detection of cs [ 1 , 6 , 15 , 16 ] . the upper normal range for baseline ufc values in most assays is between 80 and 120  g/24  h . the determination of the 24  h ufc value is the most sensitive ( 95 to 100% ) and specific ( 98% ) screening test for cs if the collection of urine is adequate as documented by creatinine excretion [ 5 , 7 ] . one meta - analysis of 15 separate studies found that baseline ufc measurement had a sensitivity of 96.6% and a specificity of 94.3% in the diagnosis of cs . a survey of 146 patients with cs also reported a sensitivity of 95% but also noted that 11% of their patients had at least one out of four ufc measurements within the reference range . thus , cs can not be excluded on the basis of a single normal baseline ufc value . multiple ufc measurements are needed because even intelligent and carefully instructed patients can make mistakes , such as not discarding the urine voided when the first day 's collection begins . furthermore , cortisol excretion in patients with cs may vary from day to day and can be cyclical , so multiple values are necessary to indicate the constancy of cortisol secretion . moreover , if there is renal impairment with a glomerular filtration rate of less than 30.0  ml / min , or an incomplete collection ( such as the urine voided to the toilet during bowel movement ) , the ufc concentration may be falsely low [ 3 , 18 ] . milder elevations of ufc levels can be found in conditions such as chronic anxiety , depression , and alcoholism , all of which are known as pseudo - cushing states , as well as in normal pregnant women . in this study , the sensitivity of baseline 24  h ufc values using a cut - off value greater than 122 or 80  g/24  h was 88.5% or 96.2% , respectively , in the all patients with cs ( table 2 ) . alexandraki and grossman   reported that the baseline ufc was almost total overlap between cs and pseudo - cushing groups . a value of ufc greater 100  nmol / l ( 3.6  g / dl ) on the second day of a 2-day lddst produced a specificity of 100% and a sensitivity of only 56% for the diagnosis of cs versus pseudo - cushing , whereas a 48  h plasma cortisol of at least 38  nmol / l ( 1.4  g / dl ) gave a specificity of 100% and a sensitivity of 90% . since the sensitivity and specificity of ufc were less than ideal when compared with other diagnostic modalities , they suggested the use of other more novel tests as first - step diagnostic tests to screen for hypercortisolemia . patients in our study often exhibited baseline morning plasma cortisol levels within the normal range ( 60% , 48 out of 80 cases ) but most had lost circadian rhythm ( 95.9% , table 2 ) . in an italian multicenter study , 37% of the patients with cs had a normal baseline plasma cortisol but 90% lacked circadian rhythm and 95% lacked suppression after overnight lddst . reported that a single sleeping midnight cortisol value greater than 1.8  g / dl resulted in 100% sensitivity for the diagnosis of cs and no overlap with controls . however , this test requires that the patient be admitted for a period of 48  h or more to avoid false - positive responses due to the stress of hospitalization . likewise , blood samples need to be drawn within 5 minutes of waking the patient . to avoid false positive results due to anticipation - related stress , these patients should not be informed that the test is to be performed . in the giraldi study , the specificity was very low ( 20.2% ) with a midnight plasma cortisol cut - off value of 1.8  g / dl ; specificity increased to 73.9% and 87.7% with 5  g / dl and 7.5  g / dl cut - off values , respectively . regardless , the measurement of midnight plasma cortisol levels is inconvenient and impractical for outpatients . our study set an easy , practical cut - off point that correlates with loss of plasma cortisol circadian rhythm ( i.e. , a baseline plasma cortisol level greater than 7.5  g / dl at 16002200  h and greater than 50% of baseline plasma cortisol level at 08000900  h ) and had a high sensitivity ( 95.9% ) for all patients with cs ( table 2 ) . the lddst is used to differentiate cs patients from those who do not have cs . found the sensitivity to be 95% for the overnight lddst using the criterion for nonsuppression of serum cortisol greater than 5  g / dl . the overnight lddst with a cut - off value of plasma cortisol levels greater than 1.8  g / dl allowed adequate sensitivity ( 98%100% ) but low specificity [ 4 , 7 ] . with a cut - off point using the traditional plasma cortisol level of greater than 5  g / dl , the overnight lddst has been reported to have a specificity of 77% to 99% depending on the population studied . lowering this cut - off would likely further decrease specificity , resulting in an increased number of false positives and potentially unnecessary evaluations . a test with near 100% sensitivity may not be a useful test if its specificity is unacceptably low . conversely , one review article reported that 38% of patients with cd retain sensitivity to dexamethasone and show suppression of plasma cortisol to less than 1.8  g / dl on overnight or 2-day lddst . thus , if clinical suspicion of cs remains high , repeated tests and other investigations are indicated . .   showed that 18% of patients with cd had plasma cortisol levels suppressed to less than 5  g / dl ( false negative ) after overnight lddst , whereas 8% actually showed suppression of plasma cortisol to less than 2  g / dl . in addition , they reported that the 2-day lddst yielded false negative results in 38% of patients when urine cortisol was tested . they recommended that neither the overnight lddst nor the 2-day lddst should be used as the sole criterion to exclude the diagnosis of cs . the hddst relies on the concept that pituitary corticotroph tumor cells in cd retain sensitivity to negative feedback effects of glucocorticoid , but this sensitivity is not observed in eas or adrenal cs [ 3 , 5 , 8 , 14 ] . the 2-day hddst in our study for the differential diagnosis of adrenal cs demonstrated a sensitivity of 95.5% using the criterion of a cut - off value of plasma cortisol levels greater than 50% of the baseline plasma cortisol level ( table 2 ) . this test demonstrated a sensitivity of 88.9% when the criterion of a cut - off value of the 24  h ufc level greater than 50% of the baseline 24  h ufc level was used . the 2-day hddst also demonstrated a sensitivity of 44.4% when using the criterion greater than 50% decrease of baseline plasma cortisol levels and a sensitivity of 85.7% when using the criterion greater than 50% decrease of the baseline 24  h ufc value for the differential diagnosis of cd ( table 2 ) . both overnight hddst and the 2-day hddst can distinguish pituitary from ectopic source of acth with a sensitivity varying from 60% to 80% and a high specificity when a cut - off value of plasma cortisol suppression above 50% is used . the 2-day hddst reportedly carries a sensitivity of 8994% and a widely ranging specificity ( from 2960% ) using the criterion of a 50% decrease in ufc levels . the overnight hddst bears a sensitivity of 7792% and a specificity of 57100% using the criterion of a 50% decrease in the plasma cortisol levels for the differential diagnosis of acth - dependent cs . .   found that 7 of 36 patients with eas ( 19% ) are suppressed to more than 50% baseline cortisol levels during the hddst . they also found that more than 60% suppression of baseline cortisol levels had the highest accuracy in excluding eas , with 80% sensitivity and 90% specificity for the diagnosis of cd . the combined criteria of a more than 30% suppression of serum cortisol during the lddst and/or a more than 20% increase in the crh test had a significantly higher sensitivity ( 97% ) and specificity ( 94% ) than the hddst or the crh tests alone in the differential of acth - dependent cs . factors that influence the poor diagnostic accuracy of the hddst include incomplete urine collection , interfering substances , episodic cortisol secretion , or inadequate levels of plasma dexamethasone due to inadequate absorption , increased clearance , or poor compliance [ 8 , 14 ] . as a result , the hddst should not be used as the sole test for the differential diagnosis of acth - dependent cs . the determination of a baseline plasma acth level is the best way to discriminate between acth - independent cs and acth - dependent cs . acth concentrations below the level of detection or 10  pg / ml at 0900  h with concomitant increased production of cortisol suggest an acth - independent cause of cs . plasma acth values greater than 20  pg / ml suggest an acth - dependent cause . for values between 10 and 20  pg / ml , a crh stimulation test is indicated . one retrospective review examined over 425 patients with cs and determined that 28% of patients with acth - independent cs had acth levels in the normal range . in addition , eight patients with adrenal adenomas had acth levels of 20  pg / ml or greater [ 4 , 15 ] . our study showed no overlap of baseline plasma acth levels between acth - independent cs and acth - dependent cs . five patients ( 11.6% ) with adrenal cs had acth levels above 20  pg / ml ( table 3 ) . reported that crh test was particularly useful for the exclusion of a pituitary adenoma in patients with acth - independent cs and normal acth levels , because acth did not respond to crh in any of these patients . on the other hand , two - day or overnight hddst may be considered for distinguishing adrenal cs from cd in cases of plasma acth levels below 30 laparoscopic adrenalectomy has become a common procedure for most benign functioning and nonfunctioning adrenal masses , as well as for patients with hyperplasia . the advantages of laparoscopic adrenalectomy as compared with open adrenalectomy include briefer postoperative hospital stay , less postoperative pain and complications , earlier oral feeding , quicker mobilization , and better postoperative quality of life and cosmetic results [ 23 , 24 ] . however , gonzalez et al .   reported an association between laparoscopic adrenalectomy for adrenocortical carcinoma and a high risk of peritoneal carcinomatosis ( 83% ) compared with open adrenalectomy ( 8% , p = 0.0001 ) . these researchers suggested that open adrenalectomy should remain the standard of care for resection of adrenal cortical neoplasms for which adrenocortical carcinoma remains in the differential diagnosis . such tumors include those with imaging characteristics suggestive of malignancy ( e.g. , heterogeneous or irregular borders ) or a transverse diameter greater than 4  cm . the most common cause of cs in our study was adrenal dependent . in the definitive diagnosis of all the cs patients , loss of plasma cortisol circadian rhythm , baseline 24  h ufc values > 80  g / dl , and overnight and 2-day lddst exhibited a high sensitivity ( 94.4100% ) . multiple ufc measurements and repeated lddst are needed if clinical suspicion of cs remains high . in the differential diagnosis of cs , baseline plasma acth concentration is the best test to discriminate between acth - independent cs and acth - dependent cs . the hddst should not be used as the sole test for the differential diagnosis of acth - dependent cs . open adrenalectomy should be reserved for cases in which adrenocortical carcinoma remains in the differential diagnosis .
from january 1987 to december 2011 , over a total of 25 years , 84 patients with cushing 's syndrome ( cs ) were identified at a medical center in southern taiwan . 
 we observed a higher incidence of acth - independent cs ( 75% ) than acth - dependent cs ( 25% ) . a higher incidence of adrenocortical adenoma ( 58.3% ) than cushing 's disease ( cd , 21.4% ) was also found . 
 the sensitivity of the definitive diagnostic tests for cs , including loss of plasma cortisol circadian rhythm , a baseline 24  h urinary free cortisol ( ufc ) value > 80  g , and overnight and 2-day low - dose dexamethasone suppression test , was between 94.4% and 100% . 
 for the 2-day high - dose dexamethasone suppression test for the differential diagnosis of cd , the sensitivity of 0800  h plasma cortisol and 24  h ufc was 44.4% and 85.7% , respectively . 
 for the differential diagnosis of adrenal cs , the sensitivities of the 0800  h plasma cortisol and 24  h ufc were 95.5% and 88.9% , respectively . in patients with acth - independent cs and acth - dependent 
 cs , the baseline plasma acth levels were all below 29  pg / ml and above 37  pg / ml , respectively . 
 the postsurgical hospitalization stay following retroperitoneoscopic adrenalectomy was shorter than that observed for transabdominal adrenalectomy ( 4.3    1.6 versus 8.8    3.7 days , p < 0.001 ) . 
 it was easy to develop retroperitoneal and peritoneal seeding of adrenocortical carcinoma via laparoscopic adrenalectomy .