The corticotropin-releasing factor test in the differential diagnosis of Cushing's syndrome: a comparison with the lysine-vasopressin test

DIAGNOSIS OF ENDOCRINE DISEASE: The role of the desmopressin test in the diagnosis and follow-up of Cushing's syndrome

Desmopressin is a vasopressin analogue selective for type 2 vasopressin receptors that mediate renal water retention. In contrast to the native hormone arginine vasopressin, a well-known ACTH secretagogue, desmopressin, exerts minimal or no activity on ACTH excretion. However, in a substantial proportion of patients with ACTH-dependent Cushing's syndrome (CS), desmopressin elicits an ACTH and cortisol response, which contrasts with the minimal responses obtained in healthy subjects. The mechanism underlying this paradoxical response involves upregulation of vasopressin type 3 and/or the aberrant expression of type 2 receptors by neoplastic ACTH-producing cells. This makes desmopressin administration a suitable test enabling the distinction between neoplastic from functional (formerly termed 'pseudo-Cushing syndrome') ACTH-dependent cortisol excess. Several studies have now established an adjunctive role of desmopressin in the initial diagnostic workup of CS. Despite some early data indicating that this test may also have a role in distinguishing between Cushing's disease (CD) and ectopic ACTH secretion, subsequent studies failed to confirm this observation. The ability of the paradoxical response to desmopressin to depict the presence of neoplastic ACTH-secreting cells was also exploited in the follow-up of patients with CD undergoing surgery. Loss of the desmopressin response, performed in the early postoperative period, was a good predictor for a favorable long-term outcome. Moreover, during follow-up, reappearance of desmopressin paradoxical response was an early indicator for recurrence. In conclusion, the desmopressin test is a valid tool in both the diagnosis and follow-up of patients with CD and should be more widely applied in the workup of these patients.

Arginine vasopressin (AVP): a review of its historical perspectives, current research and multifunctional role in the hypothalamo-hypophysial system

INTRODUCTION

This publication reviews the function of arginine vasopressin and focuses on the morphologic and functional correlation between the hormone and its effect on stress, the hypophysial-adrenocortical axis, neuroimmune responses, renal function and corticotroph pituitary tumors.

MATERIALS AND METHODS

A literature review was performed using various search engines for information regarding the morphology and the multifunctional role of arginine vasopressin.

RESULTS

Although a large number of studies were published discussing these interactions, there are several important areas that are still obscure.

CONCLUSION

The questions of how does arginine vasopressin affect the morphology and function of these various areas, and how does the secretion of ACTH and adrenocortical hormones influence the morphology of arginine vasopressin-producing cells and their hormone secretion requires further investigation.

[Paraneoplastic Cushing's syndrome, a real diagnostic and therapeutic challenge: A case report and literature review]

INTRODUCTION

Paraneoplastic Cushing's syndrome is a rare cause of endogenous hypercortisolism attributable to ectopic ACTH secretion by non-pituitary tumors. Imaging and biochemical results are often inconclusive and differential diagnosis with Cushing's disease can then be challenging. Moreover, these tumors may be occult and difficult to find and thus the need of new imaging tools such as (18)FDG-PET scan and (18)DOPA-PET scan.

CASE REPORT

We report a 50-year-old man who presented with very aggressive clinical features related to Cushing's syndrome. Biological work-up confirmed the hypercortisolism and was consistent with an ectopic ACTH secretion. Conventional localization techniques failed to show any tumor and bilateral adrenalectomy was performed because of life-threatening complications. Two years later, thoracic computed tomography reveals an 11 mm mass in the left lower pulmonary lobe, (18)FDG-PET scan found a non-specific mild hypermetabolism of the lung nodule, and the (18)DOPA-PET scan confirmed the high uptake of this nodule suggesting an endocrine carcinoma. Histology confirmed a typical carcinoid tumor. The tumor cells stained positive for ACTH, CD56, chromogranin and synaptophysin.

CONCLUSION

This case illustrates the dilemma between the need for morphological diagnosis of the ectopic ACTH source and control of the life-threatening hypercortisolism. (18)FDG-PET scan and (18)DOPA-PET scan should be considered early as a secondary diagnostic tool when conventional imagery fails to show any tumor.

Dynamic testing in Cushing's syndrome

Endogenous Cushing's syndrome (CS) results from chronic exposure to excess glucocorticoids. CS can be ACTH-dependent, caused by ACTH-secreting pituitary or ectopic tumours, or ACTH-independent, caused by cortisol-secreting adrenal tumours. CS can be an extremely difficult diagnosis to make, and assessment will include clinical, biochemical and radiological evaluation. Several screening tests are used for the confirmation of hyper-cortisolaemia and its differentiation from other, more frequent, clinical abnormalities, such as simple obesity, hypertension, depression etc. Other dynamic tests are useful for establishing the aetiology. We have reviewed the current literature on the diagnosis of CS, and based on these data and our own experience, suggest the most useful tests and diagnostic criteria to be used. We conclude that even though laboratory testing is a fundamental part of the investigation of patients with CS, the interpretation of the tests should always be performed with extreme care, as none of the tests has proven fully capable of distinguishing all cases of CS. The biochemical results should be interpreted jointly with the clinical aspects and the radiology findings in a probabilistic matrix, and not as part of a uniform algorithm.

[Cushing's syndrome due to a pulmonary carcinoid]

Cushing paraneoplasic syndrome is a rare cause of hypercorticism. We report a case of 35 year-old man presenting with Cushing's syndrome characterized by severe signs of hypercorticism and hypokalemia. Endocrine investigations were suggestive of an hypercortisolism linked to an ectopic adrenocorticotropic (ACTH) secretion, both at baseline (mean ACTH levels=275 pg/ml, urinary free cortisol excretion=3.898 mmol/24 h) and after pharmacodynamic testing (lack of inhibition of ACTH by dexamethasone). Thoracic tomodensitometric examination revealed a 15 mm tumor corresponding to a neuroendocrine pulmonary carcinoid with positive immunostaining for chromogranin A. Postoperative ACTH measurement was undetectable, plasma cortisol and free urinary cortisol were also decreased after tumor resection suggesting complete tumor removal. This case report illustrates the characteristics of paraneoplasic Cushing syndrome due to ACTH secreting pulmonary neuroendocrine carcinoid.

Evaluation and treatment of Cushing's syndrome

Cushing's syndrome results from sustained pathologic hypercortisolism caused by excessive corticotropin (ACTH) secretion by tumors in the pituitary gland (Cushing's disease, 70%) or elsewhere (15%), or by ACTH-independent cortisol secretion from adrenal tumors (15%). The clinical features are variable, and no single pattern is seen in all patients. Those features most specific for Cushing's syndrome include abnormal fat distribution, particularly in the supraclavicular and temporal fossae, proximal muscle weakness, wide purple striae, and decreased linear growth with continued weight gain in a child. Patients with characteristics of glucocorticoid excess should be screened with measurements of saliva or urine cortisol or dexamethasone suppression testing. The diagnosis of Cushing's syndrome should be followed by the measurement of plasma ACTH concentration to determine whether the hypercortisolism is ACTH-independent. In ACTH-dependent patients, bilateral inferior petrosal sinus sampling with measurement of ACTH before and after administration of ACTH-releasing hormone most accurately distinguishes pituitary from ectopic ACTH secretion. Surgical resection of tumor is the optimal treatment for all forms of Cushing's syndrome; bilateral adrenalectomy, medical treatment, or radiotherapy are sought in inoperable or recurrent cases. The medical treatment of choice is ketoconazole. The prognosis is better for Cushing's disease and benign adrenal causes of Cushing's syndrome than adrenocortical cancer and malignant ACTH-producing tumors.

Differential diagnosis and imaging in Cushing's syndrome

Establishing the cause of Cushing's syndrome (CS) is one of the most challenging processes in clinical endocrinology. Biochemical testing, including measurement of plasma adrenocorticotropin (ACTH), high-dose dexamethasone suppression, and corticotropin-releasing hormone stimulation testing, is integral to the differential diagnosis. No existing test has sufficient diagnostic accuracy when used alone, however. The adjunctive use of focused imaging, including CT, MRI, and nuclear imaging modalities, often can provide a diagnosis. In patients with ACTH-dependent CS, bilateral inferior petrosal sinus sampling can facilitate a diagnosis in those with discrepant clinical features, biochemistry, or imaging. This article focuses on current biochemical and radiologic strategies for the differential diagnosis of CS.

Cavernous and inferior petrosal sinus sampling in the evaluation of ACTH-dependent Cushing's syndrome

OBJECTIVE

Central venous sampling (CVS) is used frequently in the evaluation of ACTH-dependent Cushing's syndrome. However, several controversies exist including the diagnostic accuracy, the sampling site of choice (cavernous sinus vs. inferior petrosal sinus) and the use of lateralization data in tumour localization. We have analysed our experience with CVS to address these controversies.

DESIGN

We retrospectively reviewed CVS data in patients with ACTH-dependent Cushing's syndrome, in whom cavernous sinus sampling (CSS), inferior petrosal sinus sampling (IPSS) and IPSS after administration of ovine corticotrophin releasing hormone (oCRH) were performed.

PATIENTS

Data on 95 patients were analysed, including 79 patients with suspected Cushing's disease (CD) and 16 patients with suspected ectopic ACTH syndrome (EAS).

RESULTS

For the differential diagnosis of ACTH-dependent Cushing's syndrome, the diagnostic accuracy of IPSS after oCRH stimulation was 97% compared to 86% for CSS. While no single sampling site was perfect in diagnostic accuracy, sampling both CS and IPS achieved a combined diagnostic accuracy of 100%. Lateralization data predicted tumour location in 62-68% of the patients with various central venous drainage patterns and in 77-80% of the patients with symmetrical drainage. CSS was not significantly superior to IPSS in tumour lateralization. In patients with suspected CD based on CVS and in whom an adenoma was not found on magnetic resonance imaging (MRI) and not located by the surgeon intraoperatively, hemihypophysectomy based on lateralization data was successful in only 10 of the 18 patients (56%) with various central venous drainage patterns and in 5 of 10 patients with symmetrical drainage.

CONCLUSION

CVS is a powerful method for differentiating CD from the EAS. CSS without oCRH was not superior to IPSS after oCRH stimulation; however, we achieved a 100% diagnostic accuracy if at least two sites were sampled. Tumour localization by CVS did not accurately predict the tumour site at surgery and should not be used to guide surgical resection.

Análise crítica do cortisol salivar na avaliação do eixo hipotálamo-hipófise-adrenal

A dosagem do cortisol salivar, que avalia a fração livre do hormônio, tem se tornado cada vez mais popular, com vários ensaios comerciais disponíveis. Neste artigo avaliamos criticamente os diferentes ensaios disponíveis para dosagem de cortisol salivar e suas aplicações em situações fisiológicas e patológicas. Esta técnica tem se mostrado útil para o estudo do ritmo circadiano do cortisol e para a avaliação de insuficiência adrenal, nos primeiros dias de vida de recém-nascidos a termo e pré-termo. Adicionalmente, tem sido utilizada para avaliar o eixo hipotálamo-hipófise-adrenal (HHA) em alterações da função cognitiva, em situações de estresse, ansiedade, depressão, síndrome do pânico, na avaliação da privação de sono em pacientes trabalhadores noturnos e naqueles com fadiga crônica. Recentemente, a dosagem de cortisol salivar têm sido empregada no diagnóstico da síndrome de Cushing (SC), inclusive em crianças: sua dosagem às 24:00h apresenta sensibilidade diagnóstica superior a todos os outros parâmetros para detectar pacientes com a condição, mesmo naqueles com hipercortisolismo intermitente ou leve. Utilizando a dosagem do cortisol salivar, avaliamos a acurácia diagnóstica do teste de supressão com dexametasona (DEX, 8mg e 24mg) no diagnóstico diferencial da SC. Nossos dados sugerem que a medida do cortisol salivar, quando comparada ao cortisol plasmático, melhora a acurácia diagnóstica do teste de supressão com altas doses de DEX, mesmo utilizando critérios mais rigorosos. É importante que o pesquisador e o clínico estejam cientes das possíveis diferenças geradas pelos diferentes ensaios, para interpretarem adequadamente os intervalos de referências. Os ensaios para cortisol salivar devem ser padronizados e interpretados com base em valores de corte, obtidos em cada laboratório, utilizando amostras de controles normais da população, de obesos e de pacientes com pseudo-Cushing e SC comprovada. Os laboratórios de pesquisa ou laboratórios comerciais devem, desta forma, realizar a validação de seus ensaios para dosagem de cortisol salivar, tornando-os mais disponíveis à prática clínica.

Vasopressin as a target for antidepressant development: an assessment of the available evidence

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the key biological abnormalities described in major depressive disorder, occurring in 30-50% of depressed subjects. Corticotropin-releasing hormone (CRH) and vasopressin (AVP) are the main regulators of this stress system, with the two neuropeptides acting synergistically in bringing about adrenocorticotropin (ACTH) release from the anterior pituitary and cortisol from the adrenal gland. Based on the demonstration of elevated cerebrospinal fluid levels of CRH in depressives, and other evidence, it has been postulated that excess CRH and the resultant increased HPA forward drive form the basis of neuroendocrine dysregulation in depression. However, there is an accumulating body of evidence to support a significant role for AVP in the regulation of pituitary-adrenal activity in health and also in depressive disorder. This review, based on a Medline search from 1980 to 2001, focuses on the functional neuroanatomy, receptor pharmacology, VP synergism with CRH, and the data from clinical and pre-clinical studies that support an important role for AVP in the pathophysiology of major depression. We suggest that future antidepressants may target the vasopressinergic system.

Optimal response criteria for the human CRH test in the differential diagnosis of ACTH-dependent Cushing's syndrome

The CRH test is in widespread use for the differential diagnosis of ACTH-dependent Cushing's syndrome (CS). Despite the greater availability worldwide of human-sequence CRH (hCRH), there are no large series reporting the response criteria that best discriminate between Cushing's disease (CD) and the ectopic ACTH syndrome (EC) when using hCRH, rather than ovine-sequence CRH. We have, therefore, analyzed retrospectively the serum cortisol and plasma ACTH responses to hCRH in patients with ACTH-dependent CS, to develop response criteria that best discriminate between CD and EC. One hundred fifteen consecutive patients with proven ACTH-dependent CS were studied: 101 with CD (78 females; mean age, 40 yr; range, 10-73) and 14 with EC (7 females; mean age, 46 yr; range, 32-69). The response to hCRH was also studied in 30 normal volunteers (NVs; mean age, 29 yr; range, 20-44) with no clinical evidence of CS, and the results were compared. Following basal sampling at -15 and 0 min, hCRH (100 microg iv) was administered via an indwelling forearm cannula at 0900 h and serum cortisol and ACTH were measured at 15-min intervals for 2 h. The mean basal, peak, incremental, and percentage change in the serum cortisol and ACTH at all time points, and combination of time points, were calculated and analyzed to establish the best criteria to discriminate between CD and EC, and also between CD and NVs. The mean serum cortisol concentration in samples obtained at 15 and 30 min after CRH increased by at least 14% above the mean basal in 85 of 100 patients with CD, but in none with EC, giving a sensitivity of 85% at a specificity set at 100%. In contrast, the best plasma ACTH response of a rise of 105%, calculated from the maximal rise, gave only 70% sensitivity at 100% specificity. In the NVs, the maximum cortisol at the mean 15+30 min time point was 615 nmol/liter. Using the 15 and 30 min time points as the reference point, 71 of 100 patients with CD had a rise of serum cortisol greater than 14% and also showed an absolute cortisol level more than 615 nmol/liter. Serum cortisol responses to hCRH can be used to suggest the diagnosis of CD in the majority of patients with this condition, but it should only be used in conjunction with other biochemical and imaging modalities in establishing this important diagnosis. The measurement of plasma ACTH was less helpful in making this distinction, although it may have additional value in excluding ACTH-independent causes of CS. Although we believe that bilateral inferior petrosal sinus sampling remains the single most useful test in discriminating CD from EC in patients with ACTH-dependent CS, hCRH offers rapid diagnostic information and is a useful adjunctive test in establishing the presence of a possible ectopic source.

The desmopressin and combined CRH-desmopressin tests in the differential diagnosis of ACTH-dependent Cushing's syndrome: constraints imposed by the expression of V2 vasopressin receptors in tumors with ectopic ACTH secretion

The role of desmopressin, alone or in combination with CRH, in the differential diagnosis between Cushing's disease (CD) and ectopic ACTH secretion (EAS) still remains uncertain. Based on existing data, the desmopressin test is regarded as an alternative to the CRH stimulation test and, when given in combination with CRH, it has been suggested to completely discriminate between patients with CD and EAS. However, assessment of these tests has been limited in only a small number of patients with EAS. Desmopressin is a relatively specific V2 vasopressin receptor (V2R) agonist. Although expression of V3 vasopressin receptor (V3R) is common in tumors with EAS, the expression of V2R has not been extensively investigated. In the present study, we report our findings of the desmopressin and the combined CRH-desmopressin test in a series of patients with CD and EAS; also, the expression of V2R and V3R was investigated in tumors with EAS by a RT-PCR method. We assessed a cohort of 31 patients with ACTH-dependent Cushing's syndrome, including 26 patients with CD and five cases with histologically confirmed EAS. To avoid bias of predetermined criteria, univariate curves of the receiver operating characteristics (ROC) were constructed by plotting the sensitivity against 1-specificity at each level of the percent cortisol (F) and ACTH responses to these tests. Following desmopressin administration there was an overlap of the percent F and ACTH responses among patients with CD and EAS, and the area under the ROC curve for both these responses was not significantly different than that occurring by chance. This was also true for the percent F response following the combined CRH-desmopressin test. However, the area under the ROC curve for the percent ACTH rise following the combined test was significantly different; the point of the ROC curve closest to 1 corresponded to a percent ACTH rise of 218% (88% sensitivity and 80% specificity). Expression of V2R and V3R mRNA was investigated in four of the five excised tumors with EAS and revealed the presence of the V2R in all, whereas the V3R mRNA was expressed in three of these cases. In conclusion, in this series the desmopressin test produced a significant overlap of responses between CD and patients with EAS and, therefore, is of limited value in the differential diagnosis of the ACTH-dependent Cushing's syndrome. This is most probably due to the expression of the V2R in tumors with EAS. Moreover, following the combined CRH-desmopressin test only the ACTH but not the F responses were diagnostically useful, but still far from completely discriminating patients with CD and EAS.

Diagnóstico Laboratorial da Síndrome de Cushing

A suspeita clínica de síndrome de Cushing leva obrigatoriamente a uma avaliação laboratorial, baseada nas dosagens de cortisol e de ACTH. Entretanto as dosagens basais destes hormônios não são suficientes para confirmar o diagnóstico, sendo necessários testes dinâmicos que estimulem ou inibam o eixo hipotálamo-hipófise-adrenal (HHA). A adequada interpretação das dosagens requer o conhecimento dos princípios básicos da regulação do eixo HHA, o meio e a forma (ligada ou livre) onde o hormônio será quantificado, além das características dos ensaios empregados. Numa primeira fase do diagnóstico laboratorial, é feita a documentação do hipercortisolismo endógeno, através de dosagens salivares, urinárias ou séricas de cortisol, em amostras coletadas em horários apropriados e/ou após uso de dexametasona em doses baixas (1 mg). Numa segunda fase procede-se ao diagnóstico etiológico da síndrome de Cushing empregando-se basicamente dosagens de ACTH e de cortisol após uso de doses maiores de dexametasona. Muitas vezes a complexidade da patologia exige o uso de testes funcionais mais sofisticados, como o emprego de CRH, chegando até à necessidade de cateterismo do seio petroso inferior com coleta de amostras para a dosagem de ACTH. Apresentamos também o esquema utilizado na Divisão de Endocrinologia e Metabologia da Faculdade de Medicina de Ribeirão Preto para a confirmação da existência de síndrome de Cushing e determinação de sua etiologia.

Desmopressin stimulation test before and after pituitary surgery in patients with Cushing's disease

OBJECTIVE

The desmopressin test has been proposed as a useful tool for the differential diagnosis of Cushing's disease. The aim of our study was to investigate, in a large series of patients with Cushing's disease, the incidence of a positive ACTH and cortisol response to desmopressin. Moreover, we repeated the test soon after surgery to verify its usefulness in the assessment of early and late surgical results.

PATIENTS AND METHODS

One hundred and seven consecutive patients with Cushing's disease, 89 female and 18 male patients, with a mean age of 37.2 +/- 1.3 years, were studied. All patients, except three, repeated the test 5-6 days after surgery. Desmopressin (10 microg) was injected i.v. and blood samples were drawn 15, 30, 45 and 60 minutes thereafter. Plasma ACTH and serum cortisol were measured in duplicate by commercially available immunoassays. A positive response to desmopressin was considered to be a plasma ACTH and serum cortisol increment of at least 30% and 20% above baseline, respectively.

RESULTS

Mean basal plasma ACTH level was 17.3 +/- 1.7 pmol/l and rose to a peak level of 42.7 +/- 4.9 pmol/l at 15 minutes Mean basal serum cortisol level was 574 +/- 19 nmol/l and rose to a peak level of 814 +/- 28 nmol/l at 45 minutes. ACTH and cortisol incremental changes were inversely correlated with their respective basal levels. Ninety patients (84.1%) had an ACTH and 84 patients (78.5%) had a cortisol response to desmopressin. Several clinical and demographic characteristics were not significantly different among desmopressin responders and non responders, except that basal ACTH and cortisol levels were significantly higher in desmopressin non responders (27.2 +/- 8.3 pmol/l, 781 +/- 86 nmol/l) than in desmopressin responders (15.4 +/- 1.2 pmol/l, 535 +/- 14 nmol/l). Disappearance of the ACTH and cortisol response to desmopressin after surgery occurred in 50 of 87 (57%) ACTH responders and in 57 of 81 (70.4%) cortisol responders, respectively. However, concordance between the desmopressin test and surgical outcome was not complete. Indeed, 18 patients considered in remission still showed an ACTH increase after desmopressin and, on the contrary, four patients with disappearance of the ACTH response had persistence of hypercortisolism. During follow-up monitoring, three patients, who had persistence of the ACTH response to desmopressin, relapsed 24, 38 and 54 months after surgery.

CONCLUSIONS

Desmopressin administration elicits a significant rise in ACTH and cortisol levels in the majority but not all patients with Cushing's disease. There is a good, but not complete, concordance between the response to the desmopressin test and the surgical outcome. Our preliminary data show that persistence of the ACTH response to desmopressin in the early postoperative period might be associated with a higher risk of late relapse.

The dexamethasone-suppressed corticotrophin-releasing hormone stimulation test in anorexia nervosa

OBJECTIVE

The dexamethasone-CRH test (combination of dexamethasone-induced suppression of HPA axis function and subsequent stimulation with oCRH) (Dex-CRH test) has been proposed to fully distinguish ACTH-dependent Cushing's disease (CD) from pseudo-Cushing's states (PCS), i.e. tumoural vs. functional hypercortisolism. A plasma cortisol concentration greater than 38 nmol/l 15 min after CRH injection has been demonstrated to identify all cases of CD and to exclude all cases of PCS. Although obviously not a PCS from a clinical point of view, anorexia nervosa (AN) is associated with CRH-driven hyperactivity of the HPA axis. This study reports the response of AN patients, a model of functional biological hypercortisolism, to the Dex-CRH test.

PATIENTS AND METHODS

Nineteen women affected with anorexia nervosa and 6 healthy sex-matched controls were studied.

RESULTS

Three of 19 AN patients had an abnormal 24-h urinary free cortisol excretion (UFC), whereas 1 of 19 AN had increased overnight UFC. AN subjects had inadequately suppressed plasma cortisol after low-dose dexamethasone suppression test (LDDST) (cortisol 192.8 +/- 63.4 vs. < 27 nmol/l, AN vs. controls, respectively). Seven of 19 AN patients had plasma cortisol levels above 50 nmol/l after LDDST. None of the AN patients had CRH-induced increases in plasma ACTH or cortisol (basal cortisol 192. 8 +/- 63.4 and peak cortisol 181.7 +/- 59.9 nmol/l). Despite unresponsivenessto CRH and because of the lack of suppression after dexamethasone, using the single plasma cortisol threshold value of 38 nmol/l obtained at 15 min during the Dex-CRH test would have been misclassified in half of our AN population (9 of 19).

CONCLUSION

Since anorexia nervosa represents a model of functional hypercortisolism that shares similar pathophysiological mechanisms to the other causes of pseudo-Cushing's states, we suggest testing all causes of pseudo-Cushing's states using the dexamethasone-CRH approach to (i) describe the actual responses of clinically relevant pseudo-Cushing's states and (ii) to improve our knowledge of the pathophysiological discrepancies between the various causes of pseudo-Cushing's states. Lastly, the evaluation of dexamethasone metabolism (absorption, volume of distribution, clearance) may help to gain more insight into the diagnostic value of the dexamethasone-CRH test.

ACTH and cortisol release following intravenous desmopressin: a dose-response study

OBJECTIVE

Desmopressin (DDAVP) is a synthetic analogue of AVP, the companion regulator of corticotrophin-releasing hormone (CRH) in the control of ACTH synthesis and release from the pituitary corticotrophs. The body of evidence from human studies suggests that DDAVP alone, unlike AVP, does not bring about ACTH release, although recent evidence suggests idiosyncracies of response in healthy subjects. We examined whether DDAVP exerted any consistent effect on ACTH and cortisol release, and also if this occurred in a dose-dependant manner.

DESIGN AND SUBJECTS

A total of 18 subjects participated in the study. Saline, 5 microg, 10 microg and 15 microg DDAVP were administered as an intravenous bolus at 1300 h; 5, 7, 18 and 8 subjects, respectively, participated in each arm of the study. Plasma ACTH and cortisol responses were measured over a 120-minutes period.

RESULTS

Significant between group comparisons were demonstrated for both ACTH (P < 0.05) and cortisol responses (P < 0. 005) measured as maximum increment from baseline. The ACTH response to 5, 10 and 15 microg DDAVP was significantly greater than saline at all three doses, whilst maximal responses were seen at 10 microg. The cortisol responses to 10 and 15 microg DDAVP doses, but not 5 microg, were significantly greater than following saline. 11/18 subjects were deemed 'responders' following 10microg DDAVP on the basis of both ACTH and cortisol output.

CONCLUSIONS

This data suggests that DDAVP is capable of stimulating ACTH and cortisol release when administered alone as a bolus in over 50% of healthy subjects. This is in contrast to much of the extant literature. The mode of administration may be pertinent to this effect. This finding has implications for the recent focus on DDAVP as a diagnostic tool in disorders such as Cushing's Disease.

How do cryptogenic and symptomatic infantile spasms differ? Review of biochemical studies in Finnish patients

Infants with cryptogenic infantile spasms seem to differ from those with symptomatic spasms in having a higher cerebrospinal fluid corticotropin content, different levels of corticotropin release after exogenous vasopressin, higher serum levels of progesterone, higher dehydroepiandrosterone: androstenedione ratio (during corticotropin therapy), a higher cerebrospinal fluid gamma-aminobutyric acid content, and higher cerebrospinal fluid nerve growth factor concentrations. It remains to be seen whether the biochemical differences between the two groups are specific or only happen to correlate with the early brain damage. However, these differences would explain many pathophysiologic features of infantile spasms.

Pseudo-tumours of the thymus after correction of hypercortisolism in patients with ectopic ACTH syndrome: a report of five cases

We report the cases of four patients with occult, and one patient with overt, ectopic ACTH syndrome. Cushing's syndrome was cured by removal of the ACTH secreting tumour, op'DDD, ketoconazole or bilateral adrenalectomy. Six to 14 months after remission of hypercortisolism, follow-up computed tomography or magnetic resonance imaging of the thorax revealed in all five patients an anterior mediastinal mass 3-5 cm in length that suggested a thymic carcinoma. Exploratory thoracotomy was performed in four cases and allowed the removal of an enlarged, but normal, thymus. Histological examination revealed no tumour but showed benign thymic hyperplasia with negative immunostaining for ACTH. Thymic enlargement spontaneously disappeared 11 months after its demonstration in the patient who did not undergo thoracotomy. The mechanism of this abnormality is thought to be thymic depletion resulting from high plasma cortisol concentrations followed by 'rebound' thymic hyperplasia when cortisol levels fall. Physicians involved in the management of patients with Cushing's syndrome must be aware of this entity in order to avert a diagnostic thoracotomy.

The desmopressin stimulation test in the differential diagnosis of Cushing's syndrome

OBJECTIVE

We assessed the ability of desmopressin to stimulate the pituitary-adrenal axis in patients with Cushing's syndrome.

DESIGN AND SUBJECTS

The cortisol response to 5 ot 10 micrograms of intravenous desmopressin was evaluated in 31 patients with Cushing's syndrome of several aetiologies and in 15 normal subjects.

RESULTS

Cortisol responses were observed in 15 out of 16 patients with pituitary dependence and in two patients with adrenal nodular hyperplasia, the increase above baseline ranging from 61 to 379% in the responders. Eight patients with adrenal tumours and one with the ectopic ACTH syndrome did not respond to desmopressin, having shown changes in their cortisol levels from -5 to 42% above baseline. Responses occurred in two out of the 15 normal individuals, whose cortisol increased 58 and 69% above baseline, respectively. Stimulation tests with standard agents as lysine vasopressin or ovine corticotrophin-releasing hormone were performed in the same patients and there was a high degree of concordance. No serious adverse reactions were observed in the tests with desmopressin.

CONCLUSIONS

Desmopressin was able to stimulate the pituitary-adrenal axis in patients with Cushing's disease and, like corticotrophin releasing hormone, it may prove useful in the differential diagnosis of Cushing's syndrome.

Potentiation of the classic ovine corticotrophin releasing hormone stimulation test by the combined administration of small doses of lysine vasopressin

OBJECTIVE

To assess the corticotrophic response to ovine corticotrophin releasing hormone (CRH) with the lowest dose of lysine vasopressin able to induce both the greatest stimulation and the lowest degree of side-effects.

SUBJECTS

Fourteen healthy young adult males.

DESIGN

Increasing intravenous doses (either 0, 0.03, 0.1, 0.3, or 1 IU) of lysine vasopressin, infused over 20 minutes, combined with a bolus of 100 micrograms ovine CRH.

MEASUREMENT

Radioimmunoassay of plasma ACTH, lipotrophin hormones and cortisol levels.

RESULTS

(1) Responses to stimulation tests were evaluated as the area under the curves of plasma levels versus sample times, from 0 to 120 minutes after injection or start of perfusion (six subjects). The lowest dose of lysine vasopressin that induced an additional stimulation in the CRH-stimulated ACTH response was 0.3 IU. The combination of 1 IU lysine vasopressin with CRH doubled values of the area under the curve for the ACTH. Lysine vasopressin alone (0.3 and 1 IU) failed to stimulate ACTH responses. (2) The combined test (100 micrograms CRH and 1 IU lysine vasopressin) was carried out on eight additional control subjects. From a mean basal level of 23 +/- 5.6 (SEM), plasma ACTH peaked to 104.5 +/- 8 ng/l (23.0 +/- 1.8 pmol/l) as early as 20-30 minutes after the start of injection. When repeated after a two-week interval, the combined test induced identical stimulation in a given subject. Results of lipotrophin hormone determinations roughly paralleled those of ACTH. However the effects on cortisol levels were less clear. Subjects injected with CRH experienced slight facial flush. Following the 1 IU lysine vasopressin dosage, side-effects were reduced to skin pallor. No changes in heart-rate or blood-pressure were observed.

CONCLUSIONS

Under these conditions, the combination of 100 micrograms CRH with 1 IU lysine vasopressin constitutes a powerful test for direct assessment of the pituitary reserve and therefore can be employed as a routine investigational tool.