Distinguishing Cushing's disease from the ectopic ACTH syndrome: Needles in a haystack or hiding in plain sight?

Ectopic Cushing's Syndrome in Advanced Small-Cell Lung Cancer (SCLC): Clinical Challenges and Therapeutic Insights

BACKGROUND/OBJECTIVES

Ectopic Cushing's syndrome (ECS) is a rare, life-threatening condition caused by uncontrolled ACTH secretion from tumors, most commonly small-cell lung cancer (SCLC). ECS is traditionally reported in 1-6% of SCLC cases; however, recent data suggest it may be much higher. This study compares the clinical presentation of SCLC-related ECS (ECS-SCLC) with other ECS etiologies and analyzes the diagnosis, treatment, and outcomes of ECS-SCLC.

METHODS

We retrospectively analyzed the records of 39 ECS patients diagnosed between 2000 and 2024 at a tertiary endocrinology center. Seven cases (18%) were due to SCLC. Diagnosis was based on clinical signs, biochemical testing, imaging, and histopathology.

RESULTS

ECS-SCLC patients (five men, two women; median age 61), compared to other ECS etiologies, had a shorter time to diagnosis (median 1 vs. 2 months; p = 0.03), worse general condition (ECOG 4 vs. 3; p = 0.01), greater muscle weakness (Lovett scale median 2[IQR 1-2] vs. 2[IQR 2-3]; p = 0.04), more severe hypokalemia (2.12 vs. 2.7 mmol/L; p = 0.03), and required higher potassium supplementation (200 vs. 120 mEq/day; p = 0.001). All ECS-SCLC patients experienced weight loss (median 5 kg). Cortisol-lowering therapy (metyrapone or osilodrostat) was initiated in six patients (mean initiation time 3.7 days), leading to clinical improvement. Oncological treatment (chemotherapy or radiotherapy) was administered in five patients after stabilization. The median follow-up time was 3 months.

CONCLUSIONS

Early recognition of ECS-SCLC and a multidisciplinary approach are critical. Severe hypokalemia and muscle weakness should prompt timely evaluation for hypercortisolism. Cortisol-lowering therapy may improve clinical status and facilitate oncological treatment.

A Rare Case of Metastatic Adrenocorticotrophic Hormone - Secreting Pancreatic Neuroendocrine Tumor Causing Ectopic Cushing Syndrome in a 46-Year-Old Woman

BACKGROUND Adrenocorticotrophic hormone (ACTH)-secreting pancreatic neuroendocrine tumors (pNETs) are rare and poorly understood entities. Only 1-2% of pancreatic neoplasms are pNETs, and even fewer are hormone-secreting. They can present indolently or with overt Cushing syndrome. Their diagnosis involves complex multi-modal imaging and laboratory evaluation. Management includes medications, such as somatostatin analogs and ketoconazole, as well as surgical resection for definitive treatment. This report describes a 46-year-old woman who presented with overt Cushing syndrome and was ultimately diagnosed with a pNET. CASE REPORT This patient's initial symptoms and laboratory testing were consistent with Cushing syndrome. A high-dose dexamethasone suppression test suggested ectopic ACTH production, and magnetic resonance imaging (MRI) of the brain showed a pituitary microadenoma. However, computed tomography (CT) of the abdomen and endoscopic ultrasound-guided biopsy with immunohistochemistry confirmed a pancreatic mass as the source of ACTH production with potential hepatic metastasis. Her Cushing syndrome was managed with ketoconazole and octreotide. Subsequently, >99% of the pNET was surgically removed, resulting in reversal of her Cushing syndrome. Currently, she is being monitored closely for recurrence. CONCLUSIONS Our management of this ACTH-secreting pNET highlights the complexities of diagnosis and multidisciplinary treatment options, which are underrepresented in the current literature on this rare entity. This case emphasizes the challenges in evaluation, including the importance of early and precise diagnosis in the face of potential confounders.

Ectopic ACTH syndrome secondary to small-cell oropharyngeal cancer

A woman in her 80s with known metastatic small-cell oropharyngeal cancer was admitted after a fall. There was proximal limb weakness with hypertension, metabolic alkalosis, hypokalaemia and hyperglycaemia. CT scans revealed progression of her cancer with enlarging liver and lung metastases. Her admission was complicated by delirium and progressive dysphagia relating to her primary oropharyngeal malignancy. Cortisol and adrenocorticotropic hormone (ACTH) were markedly raised and were not suppressed after overnight and high-dose dexamethasone tests. Typical clinical features of Cushing's syndrome were absent. She was diagnosed with ectopic ACTH syndrome secondary to small-cell oropharyngeal cancer. Metyrapone and spironolactone were commenced; however, the patient deteriorated, and a decision was made to prioritise her comfort over escalating treatment.

Cushing syndrome

Cushing syndrome (CS) is a constellation of signs and symptoms caused by excessive exposure to exogenous or endogenous glucocorticoid hormones. Endogenous CS is caused by increased cortisol production by one or both adrenal glands (adrenal CS) or by elevated adrenocorticotropic hormone (ACTH) secretion from a pituitary tumour (Cushing disease (CD)) or non-pituitary tumour (ectopic ACTH secretion), which stimulates excessive cortisol production. CS is associated with severe multisystem morbidity, including impaired cardiovascular and metabolic function, infections and neuropsychiatric disorders, which notably reduce quality of life. Mortality is increased owing to pulmonary emboli, infection, myocardial infarction and cerebrovascular accidents. The clinical presentation is variable and because some CS signs and symptoms are common in the general population, the diagnosis might not be considered until many features have accumulated. Guidelines recommend screening patients with suspected CS with 24-h urine cortisol, bedtime salivary cortisol and/or 1 mg dexamethasone suppression test. Subsequently, determining the aetiology of CS is important as it affects management. The first-line therapy for all aetiologies of endogenous CS is surgical resection of the causal tissue, including corticotroph adenoma or ectopic tumour for ACTH-dependent CS or unilateral or bilateral adrenalectomy for adrenal CS. Second-line therapies include steroidogenesis inhibitors for any cause of CS, pituitary radiation (with or without steroidogenesis inhibitors) for CD, and bilateral adrenalectomy for ACTH-dependent causes of CS.

Personalized Noninvasive Diagnostic Algorithms Based on Urinary Free Cortisol in ACTH-dependant Cushing's Syndrome

CONTEXT

Current guidelines for distinguishing Cushing's disease (CD) from ectopic ACTH secretion (EAS) are questionable, as they use pituitary magnetic resonance imaging (MRI) as first-line investigation for all patients. CRH testing is no longer available, and they suggest performing inferior petrosal sinus sampling (BIPPS), an invasive and rarely available investigation, in many patients.

OBJECTIVE

To establish noninvasive personalized diagnostic strategies based on the probability of EAS estimated from simple baseline parameters.

DESIGN

Retrospective study.

SETTING

University hospitals.

PATIENTS

Two hundred forty-seven CD and 36 EAS patients evaluated between 2001 and 2023 in 2 French hospitals. A single-center cohort of 105 Belgian patients served as external validation.

RESULTS

Twenty-four-hour urinary free cortisol (UFC) had the highest area under the receiver operating characteristic curve for discrimination of CD from EAS (.96 [95% confidence interval (CI), .92-.99] in the primary study and .99 [95% CI, .98-1.00] in the validation cohort). The addition of clinical, imaging, and biochemical parameters did not improve EAS prediction over UFC alone, with only BIPPS showing a modest improvement (C-statistic index .99 [95% CI, .97-1.00]). Three groups were defined based on baseline UFC: < 3 (group 1), 3-10 (group 2), and > 10 × the upper limit of normal (group 3), and they were associated with 0%, 6.1%, and 66.7% prevalence of EAS, respectively. Diagnostic approaches performed in our cohort support the use of pituitary MRI alone in group 1, MRI first followed by neck-to-pelvis computed tomography scan (npCT) when negative in group 2, and npCT first followed by pituitary MRI when negative in group 3. When not combined with the CRH test, the desmopressin test has limited diagnostic value.

CONCLUSION

UFC accurately predicts EAS and can serve to define personalized and noninvasive diagnostic algorithms.

Unusual Presentation of Case of a Lung Carcinoid Tumor With Ectopic Adrenocorticotropic Secretion (EAS) Associated With Acute Weight Gain and Peripheral Edema

Ectopic adrenocorticotropic secretion (EAS) is classically related to small-cell lung cancer but is caused by a wide variety of tumors. In approximately one-fifth of cases, the cause remains unidentified. Excess adrenocorticotropic hormone (ACTH) leads to Cushing's syndrome, and the presentation can be due to biochemical derangements such as hypokalemia and hyperglycemia. Alternatively, it may manifest with secondary symptoms such as weight gain, hypertension, skin thinning, abdominal striae, and/or psychotic manifestations. The diagnosis is established through dynamic testing after confirming excess cortisol and ACTH levels. Imaging is then used to identify the hormonally active lesion. Controlling hypercortisolism with steroidogenesis inhibitors is the initial step before proceeding to definitive treatment. Ideally, tumor resection, if possible, but bilateral adrenalectomies are considered in cases not amenable to curative surgery.

Cushing's syndrome

Endogenous Cushing's syndrome results from excess glucocorticoid secretion, which leads to a myriad of clinical manifestations, comorbidities, and increased mortality despite treatment. Molecular mechanisms and genetic alterations associated with different causes of Cushing's syndrome have been described in the last decade. Imaging modalities and biochemical testing have evolved; however, both the diagnosis and management of Cushing's syndrome remain challenging. Surgery is the preferred treatment for all causes, but medical therapy has markedly advanced, with new drug options becoming available. Nevertheless, several comorbidities remain even after patient remission, which can affect quality of life. Accurate and timely diagnosis and treatment are essential for mitigating chronic complications of excess glucocorticoids and improving patient quality of life. In this Seminar, we aim to update several important aspects of diagnosis, complications, and treatment of endogenous Cushing's syndrome of all causes.

Ectopic Hormonal Syndromes: Cushing's Syndrome and Acromegaly

Ectopic hormone production may be present in neuroendocrine and non-endocrine neoplasms. Ectopic sources of growth hormone, adrenocorticotropin (ACTH), or their releasing factors are uncommon but clinically relevant. Ectopic ACTH tumors have been studied more than the rest, but there are still no comprehensive multidisciplinary guidelines that include all the pitfalls in the diagnosis and management of ectopic hormonal syndromes and the neoplasms associated with ectopic Cushing or acromegaly. The frequency of neuroendocrine neoplasms and other neoplasms with neuroendocrine differentiation has been increasing in recent decades. The review of the available data on these tumors, their classification, and improvements in diagnostic and therapeutic procedures is important to understand the relevance of ectopic Cushing's syndrome and acromegaly in clinical practice.

Non-Invasive Biochemical Testing of ACTH-dependent Cushing's Disease: Do We Still Need Petrosal Sinus Sampling?

Differentiating between a pituitary from an ectopic source of ACTH could be a real one of the major challenges of clinical endocrinology. The Bilateral inferior petrosal sinus sampling (BIPSS) is considered the gold standard for identifying the source of ACTH; however, is not available worldwide. After the SARS-CoV-2 pandemic, algorithms that include biochemical and imaging tests have gained importance as an alternative to BIPSS. This review summarizes the drawbacks in the differential diagnosis of ACTH-dependent Cushing; the evolution of diagnostic tests, and the evidence that exists on their performance. As well as a comparison between the advantages and disadvantages of invasive and non-invasive tests.

The relationship between temporal muscle thickness and disease activity in Cushing's disease

OBJECTIVE

This study aimed to investigate the relationship between hypercortisolism and temporal muscle thickness (TMT) in Cushing's disease (CD).

METHODS

A retrospective review of medical records was conducted for patients with CD who presented to our clinic between 2012 and 2022. Biochemical data and TMT measurements from sella imaging were evaluated during diagnosis and the first postoperative year.

RESULTS

A total of 44 patients were included in the study, with an average age of 43.9 years, of which 38 were female. The mean TMT at the time of diagnosis was 19.07 ± 1.71 mm, with no significant difference between males and females (p = 0.097), and no correlation between the TMT and age at diagnosis (p = 0.497). There was an inverse relationship between TMT and serum cortisol levels, 24-h UFC, and midnight salivary cortisol at the time of diagnosis of CD (p < 0.05, for all). One year after surgery, TMT significantly increased in all patients compared to baseline (p < 0.001). Furthermore, patients who achieved postoperative remission had significantly higher TMT values compared to those who did not achieve remission (p = 0.043). Among the patients who achieved remission, those who achieved remission through surgery had significantly higher TMT compared to those who could not reach remission with surgery and patients who started medical treatment and achieved biochemical remission (p = 0.01). Patients with severe myopathy and sarcopenia had significantly lower TMT values than the others (p < 0.001).

CONCLUSION

Temporal muscle thickness was found to be associated with disease activity and disease control in Cushing's disease.

Surgery and perioperative management of patients with Cushing's disease

Transsphenoidal surgery (TSS) is the initial treatment modality of first choice in Cushing's disease (CD). With microscopic TSS and endoscopic TSS, two operative techniques with equally favourable remission rates and operative morbidity are available. On average, remission is achieved with primary TSS in 80% of patients with microadenomas and 60% of patients with macroadenomas. The current literature indicates that remission rates in repeat TSS for microadenomas can also exceed 70%. Experience with TSS in CD plays an important role in the success rate and centralization in Pituitary Centres of Excellence has been proposed. Microadenoma stage, imaging-visible adenoma, confirmation of ACTH-positive adenoma on histopathology and noninvasiveness are positive predictors for postoperative remission. In postoperative management, a steroid-sparing protocol with early postoperative assessment of remission status is recommended. Convincing evidence suggests that prolonged postoperative prophylactic antithrombotic measures can significantly reduce the risk of postoperative thromboembolic events in CD. Prevention or successful treatment of cortisol withdrawal syndrome remains an unsolved issue that should be a focus of future research. The further development and broad availability of functional imaging hold promise for improved preoperative detection of microadenomas. Intraoperative identification of microadenomas by specific fluorescent targeting could be a promising future avenue for the treatment of patients with negative imaging.

Long-term morbidity and mortality in patients with Cushing's syndrome

Increased multisystem morbidity and mortality in patients with Cushing's syndrome comprise clinical problems and challenges, both at the time of diagnosis and in remission. Relevant comorbidities and clinical problems include hypertension, diabetes, overweight, myopathy and a high risk for acute complications such as infections and venous thrombembolism. Although there are therapy recommendations for most of these comorbidities, there is a lack of large, prospective studies to confirm and optimise them. Mortality is especially high during active disease and within the first year after diagnosis, as a result of cardiovascular events, infections and suicide. All in all, interdisciplinary therapy management is important for reducing morbidity and mortality over the long-term.

Clinical presentation and etiology of Cushing's syndrome: Data from ERCUSYN

This review presents the data on clinical presentation at diagnosis in 1564 patients included in the European Registry on Cushing's syndrome (ERCUSYN), of whom 1045 (67%) had pituitary-dependent Cushing's syndrome (CS) (PIT-CS), 385 (25%) had adrenal dependent CS (ADR-CS) and 89 (5%) had ectopic adrenocorticotropic hormone syndrome (ECT-CS). The most frequent symptoms in the overall series were weight gain (83%), hypertension (79%), skin alterations (76%) and myopathy (70%). Diabetes mellitus was present in 32% and depression in 35% of patients. Skin alterations, menstrual irregularities and reduced libido were more prevalent in PIT-CS patients compared to ADR-CS patients, whereas patients with ECT-CS more frequently had diabetes mellitus, myopathy, hirsutism and vertebral fractures compared to the other etiologies, consistent with a more severe clinical scenario. Reduced libido and bone fractures were more prevalent in men compared to women. Quality of life was poor at diagnosis, irrespective of the etiology of CS, and also associated with the presence of depression at baseline. A delay of 2 years between the onset of symptoms and diagnosis was also observed, with a high number of specialists consulted, who often missed the correct diagnosis. To develop strategies aimed at shortening the time elapsed to diagnosis, it is important to rapidly start treatment and reduce the burden of the disease on patient psychophysical health and longevity.

The diagnosis and management of Cushing's syndrome in pregnancy

Endogenous Cushing's syndrome (CS) is rarely encountered during pregnancy. Clinical and biochemical changes in healthy pregnancy overlap with those seen in pregnancy complicated by CS; the diagnosis is therefore challenging and can be delayed. During normal gestation, adrenocorticotrophic hormone, corticotrophin-releasing hormone, cortisol, and urinary free cortisol levels rise. Dexamethasone administration fails to fully suppress cortisol in pregnant women without CS. Localisation may be hindered by non-suppressed adrenocorticotrophic hormone levels in a large proportion of those with adrenal CS; smaller corticotroph adenomas may go undetected as a result of a lack of contrast administration or the presence of pituitary hyperplasia; and inferior petrosal sinus sampling is not recommended given the risk of radiation and thrombosis. Yet, diagnosis is essential; active disease is associated with multiple insults to both maternal and foetal health, and those cured may normalise the risk of maternal-foetal complications. The published literature consists mostly of case reports or small case series affected by publication bias, heterogeneous definitions of maternal or foetal outcomes or lack of detail on severity of hypercortisolism. Consequently, conclusive recommendations, or a standardised management approach for all, cannot be made. Management is highly individualised: the decision for surgery, medical control of hypercortisolism or adoption of a conservative approach is dependent on the timing of diagnosis (respective to stage of gestation), the ability to localise the tumour, severity of CS, pre-existing maternal comorbidity, and, ultimately, patient choice. Close communication is a necessity with the patient placed at the centre of all decisions, with risks, benefits, and uncertainties around any investigation and management carefully discussed. Care should be delivered by an experienced, multidisciplinary team, with the resources and expertise available to manage such a rare and challenging condition during pregnancy.

Aggressive corticotroph tumors and carcinomas

Pituitary tumors are generally benign, although in rare cases aggressive pituitary tumors (APTs) and carcinomas present important diagnostic and therapeutic challenges and are associated with a high mortality rate. Almost half of these APTs and carcinomas are corticotroph tumors, suggesting a specific prognosis. Clinical, pathological and molecular prognostic markers are limited and do not allow early management of these tumors. Temozolomide remains the first-line treatment once a diagnosis of aggressive pituitary tumor or carcinoma has been made. Novel alternative treatments exist, including immune checkpoint inhibitors, which can be used in the case of temozolomide treatment failure. The aim of this review is to present the clinical, pathological and molecular characteristics of aggressive corticotroph tumors and carcinomas, and to describe the results obtained with currently available treatments.

Pituitary MRI in Cushing's disease - an update

Pituitary MRI is essential in the diagnosis of ACTH-dependent Cushing's syndrome, but its results are inconsistent. The demonstration of a sellar image compatible with the diagnosis of corticotropinoma varies from 40% to 90%, depending on the centre where the imaging is performed. In fact, the expertise of the neuroradiologist, use of a Tesla 3.0 MRI and choice of sequences are fundamental. The T2 and 3D gradient echo sequences after gadolinium injection are the most informative and today allow the detection of macro- and microadenomas in almost all cases. The diagnosis of numerous picoadenomas (<3-4 mm) is more challenging. The 2D and 3D spin echo or delayed T1 SE or FLAIR sequences after gadolinium can be used as a complement or to confirm a suspicious image. Characterization of corticotropinomas remains problematic. However, the correct assessment of so-called incidentalomas by recognizing artifacts, anatomical variants and frequent Rathke's cleft cysts eliminates around 90% of the incidentalomas that mimic pituitary adenomas, as repetitively reported in the literature. For the time being, there is reason to believe that hybrid imaging combining PET and MRI such as 11C-methionine PET coregistered with volumetric MRI will solve the diagnosis of corticotropinomas in the near future.

Hypothalamic-pituitary-adrenal axis recovery after treatment of Cushing's syndrome

After successful treatment for Cushing's syndrome (CS), secondary adrenal insufficiency develops as a result of the prior suppression of the hypothalamic-pituitary-adrenal (HPA) axis by excess cortisol in the body. Until the recovery of the HPA axis, glucocorticoid replacement therapy is required to enable normal functioning of the body and prevent adrenal crisis. Significant variation in the median time of recovery of the HPA axis is found in various cohorts of CS patients ranging from several weeks to years. Despite the use of physiological glucocorticoid replacement, after cure for CS, patients often experience symptoms of glucocorticoid withdrawal syndrome (GWS). The optimal glucocorticoid regimen to reduce GWS needs to be established and requires an individualized approach aiming to avoid overtreatment at one side and minimize the risk of undertreatment and possible adrenal crisis and GWS on the other side.

The corticotroph cells from early development to tumorigenesis

During development, highly specialized differentiated cells, such as pituitary secretory cells, acquire their identity and properties through a series of specification events exerted by transcription factors to implement a unique gene expression program and epigenomic state. The investigation of these developmental processes informs us on the unique features of a cell lineage, both to explain these features and also to outline where these processes may fail and cause disease. This review summarizes present knowledge on the developmental origin of pituitary corticotroph and melanotroph cells and on the underlying molecular mechanisms. At the onset, comparison of gene expression programs active in pituitary progenitors compared to those active in differentiated corticotrophs or melanotrophs indicated dramatic differences in the control of, for example, the cell cycle. Tpit is the transcription factor that determines terminal differentiation of pro-opiomelanocortin (POMC) lineages, both corticotrophs and melanotrophs, and its action involves this switch in cell cycle control in parallel with activation of cell-specific gene expression. There is thus far more to making a corticotroph cell than just activating transcription of the POMC gene. Indeed, Tpit also controls implementation of mechanisms for enhanced protein translation capacity and development of extensive secretory organelles. The corticotroph cell identity also includes mechanisms responsible for homotypic cell-cell interactions between corticotrophs and for privileged heterotypic cell interactions with pituitary cells of other lineages. The review also summarizes current knowledge on how a pioneer transcription factor, Pax7, remodels the epigenome such that the same determination transcription factor, Tpit, will implement the melanotroph program of gene expression. Finally, this canvas of regulatory mechanisms implementing POMC lineage identities constitutes the background to understand alterations that characterize corticotroph adenomas of Cushing's disease patients. The integration of all these data into a unified scheme will likely yield a scheme to globally understand pathogenic mechanisms in Cushing's disease.

Role of radiosurgery in the treatment of Cushing's disease

Radiotherapy is a useful adjuvant treatment for patients with Cushing's disease that is not cured by surgery. In particular, Gamma Knife radiosurgery (GKRS) has been increasingly used worldwide as the preferred radiation technique in patients with persistent or recurrent Cushing's disease. The most widely accepted criterion for hormonal remission after GKRS is normalization of urinary free cortisol (UFC) levels. When a clear biological target is not identified, irradiation of the whole pituitary gland can be considered. The 5-year probability of remission is 65%-75%. Normalization of hypercortisolism usually occurs within 3 years from GKRS treatment and control of tumor growth is optimal, approaching more than 90%. No clear predictor of a favorable outcome has emerged up to now, except for the experience of the treating team. In the largest series, development of partial or complete hypopituitarism occurred between 15% and 36%. Severe side effects of GKRS, such as optic neuropathy and oculomotor palsy, are uncommon but have been documented in patients previously exposed to radiation. Recurrence of disease has been reported in as high as 16%-18% of the patients who achieved normalization of UFC levels in the two largest series, whereas smaller series did not describe late failure of GKRS. The reason for this discrepancy is unclear, as is the relationship between hormonal and tumoral recurrence. Another unresolved issue is whether treatment with adrenal blocking drugs can jeopardize the results of GKRS. GKRS is an effective second-line treatment in patients with Cushing's disease not cured by surgery. Hypopituitarism is the most frequent side effect of GKRS, whereas severe neurologic complications are uncommon in radiation-naïve patients.

Long-term follow-up and predictors of recurrence of Cushing's disease

Transsphenoidal surgery is the first-line treatment for Cushing's disease to selectively remove the tumor. The rate of postoperative remission is estimated around 70%-80% in expert centers. However, the long-term remission rate is lower because of recurrence during follow-up that can be observed in 15% to 25% of the patients depending on the studies and duration of follow-up. There is no significant predictive factor of recurrence before surgery, but postoperative corticotroph insufficiency and its duration has been found to be a protective factor for recurrence in many studies. The persistence of a positive response to desmopressin after surgery is associated with a higher rate of recurrence. Long term monitoring for recurrence with annual clinical and hormonal investigations after the hypothalamic-pituitary-adrenal axis postoperative recovery is advised. The biological tests used for the diagnosis of Cushing's syndrome (24 h-urinary-free cortisol [UFC], late-night salivary or serum cortisol, 1 mg dexamethasone suppression test) can be used to screen for recurrence. Several studies report that increased late night cortisol and alterations of dynamic testing can be observed before the increased 24 h-UFC. For this reason it is suggested that late-night salivary cortisol would be a very sensitive tool to diagnose recurrence, pending the realization of several assays in case of borderline or discrepant result. This review will summarize the knowledge about recurrence of Cushing's disease after pituitary surgery and the current recommendations for its monitoring and diagnosis.

Glucose and lipid metabolism abnormalities in Cushing's syndrome

Prolonged excess of glucocorticoids (GCs) has adverse systemic effects leading to significant morbidities and an increase in mortality. Metabolic alterations associated with the high level of the GCs are key risk factors for the poor outcome. These include GCs causing excess gluconeogenesis via upregulation of key enzymes in the liver, a reduction of insulin sensitivity in skeletal muscle, liver and adipose tissue by inhibiting the insulin receptor signalling pathway, and inhibition of insulin secretion in beta cells leading to dysregulated glucose metabolism. In addition, chronic GC exposure leads to an increase in visceral adipose tissue, as well as an increase in lipolysis resulting in higher circulating free fatty acid levels and in ectopic fat deposition. Remission of hypercortisolism improves these metabolic changes, but very often does not result in full resolution of the abnormalities. Therefore, long-term monitoring of metabolic variables is needed even after the resolution of the excess GC levels.

Genetics of Cushing's disease

Corticotroph tumours are primarily sporadic monoclonal neoplasms and only rarely found in genetic syndromes. Recurrent mutations in the ubiquitin specific protease 8 (USP8) gene are found in around half of cases. Mutations in other genes such as USP48 and NR3C1 are less frequent, found in less than ~20% of cases. TP53 and ATXR mutations are reported in up to one out of four cases, when focusing in USP8 wild type or aggressive corticotroph tumours and carcinomas. At present, USP8 mutations are the primary driver alterations in sporadic corticotroph tumours, TP53 and ATXR mutations may indicate transition to more aggressive tumour phenotype. Next generation sequencing efforts have identified additional genomic alterations, whose role and importance in corticotroph tumorigenesis remains to be elucidated.

Medical management of Cushing's disease: When and how?

Transsphenoidal surgery is the first-line treatment of Cushing's disease. However, medical treatment can be given in a high proportion of patients with this rare condition. This is especially the case in severe hypercortisolism for which medical treatment will be given for a short period of time to prepare the patient for surgery, or on a long-term basis after failed transsphenoidal surgery, or when waiting for the maximal beneficial effect of radiation techniques. These different situations all require that hypercortisolism be perfectly controlled. Severe hypercortisolism is frequently treated by a block and replace approach during which a substitutive treatment is given after the induction of adrenal insufficiency. Mild hypercortisolism, the most frequent situation, is usually treated with a titration approach with a progressive dose increase. This approach requires certainty of eucortisolism because patients may be treated for a prolonged period. This review details the main situations during which medical treatment should be considered, as well as the way in which to monitor them to avoid the long-term consequences of mild hypo- or hypercortisolism.

Long-term effects of glucocorticoid excess on the brain

The metabolic and cardiovascular clinical manifestations in patients with Cushing's syndrome (CS) are generally well known. However, recent studies have broadened the perspective of the effects of hypercortisolism, showing that both endogenous and exogenous glucocorticoid excess alter brain functioning on several time scales. Consequently, cognitive deficits and neuropsychological symptoms are highly prevalent during both active CS and CS in remission, as well as during glucocorticoid treatment. In this review, we discuss the effects of endogenous hypercortisolism and exogenously induced glucocorticoid excess on the brain, as well as the prevalence of cognitive and neuropsychological deficits and their course after biochemical remission. Furthermore, we propose possible mechanisms that may underly neuronal changes, based on experimental models and in vitro studies. Finally, we offer recommendations for future studies.

Diagnostic workup of Cushing's syndrome

Cushing's syndrome (CS) is a rare but detrimental endocrine disorder. Early diagnosis and prompt treatment are essential since the duration of hypercortisolism has an adverse impact on the extent of comorbidities and overall survival. The diagnostic approach involves a stepwise process that includes (1) screening and confirming the diagnosis and (2) establishing the aetiology of CS. The tests currently used to confirm the diagnosis of CS include urinary free cortisol measurements, the dexamethasone suppression test and late- night salivary cortisol or midnight serum cortisol measurements. None of these tests are ideal; all have pitfalls and require careful interpretation. Following confirmation of CS, measurement of ACTH discriminates between ACTH-dependent and non-ACTH dependent causes of CS. Adrenal imaging provides clues for the aetiology of non-ACTH dependent forms. Differentiation between the ACTH-dependent forms that involve pituitary corticotroph adenomas and ectopic ACTH sources is more complex and include pituitary MRI imaging, the high dose dexamethasone suppression test, the CRH test, bilateral inferior petrosal sinus sampling and, when required imaging modalities to detect ectopic ACTH secreting lesions. This review, which is part of a special issue on "Update of Cushing's syndrome: 100 years after Minnie G" will provide an update on our current diagnostic workup for the confirmation and differential diagnosis of CS.