Endogenous neoplastic hypercortisolism - Cushing syndrome (CS) - is one of the most challenging diagnostic and management problems in clinical endocrinology. CS may be due to either a pituitary tumor (Cushing disease, CD), or a non-pituitary (ectopic) tumor secreting ACTH. ACTH-independent hypercortisolism due to unilateral or bilateral adrenal nodular disease has been increasingly recognized as an important cause of CS. Regardless of the cause of CS, the clinical manifestations are protean and include a myriad of clinical, biochemical, neurocognitive, and neuropsychiatric abnormalities. The catabolic state of hypercortisolism causes signs and symptoms including skin fragility, bruising, delayed healing, violaceous striae, muscle weakness, and low bone mass with fragility fractures. Other clinical features include weight gain, fatigue, depression, difficulty concentrating, insomnia, facial plethora, and fat redistribution to the head and neck with resultant supraclavicular and dorsocervical fullness[
1]. Metabolic consequences of hypercortisolism including hypertension, diabetes, and dyslipidemia are common. In addition, women often experience hirsutism and menstrual irregularity, while men may have hypogonadism.
Management options of CS include surgery, medications, and radiation. The preferred first line treatment, regardless of source, is surgery, which offers the potential for remission[
2‐
4]. The primary literature, reviews, and clinical practice guidelines for CS have traditionally focused on the diagnosis, subtyping, and surgical approach to CS. This bias derives first from the profound diagnostic challenge posed in the evaluation of cortisol production and dynamics, given that circulating cortisol follows a circadian rhythm, exhibits extensive protein binding and metabolism, and rises acutely with stress. CD and ectopic ACTH syndrome may be difficult to distinguish clinically and biochemically, and inferior petrosal sinus sampling is required in many patients to resolve this differential diagnosis. Ectopic ACTH-producing tumors can also be small, and these tumors can escape localization despite the best current methods. Although diagnosis and initial surgical remission can be achieved in the majority of patient with CS at experienced centers, up to 50% of patients with CD will require additional therapies after unsuccessful primary surgeries or recurrence up to many years later[
5]. For patients who do not achieve surgical cure or who are not surgical candidates, several medical treatment options are now available. Pharmacotherapies directed at the pituitary include pasireotide[
6,
7] (FDA approved) and cabergoline[
8]. Adrenal steroidogenesis inhibitors such as osilodrostat[
9] (FDA approved), metyrapone[
10], levoketoconazole[
11] (FDA approved) and ketoconazole[
12], as well as the glucocorticoid antagonist, mifepristone[
13] (FDA approved), are now widely used to treat CS. Pituitary radiotherapy is an additional treatment option for CD but can take months to years to lower cortisol production. Bilateral adrenalectomy (BLA) provides immediate, reliable correction of hypercortisolism but mandates life-long corticosteroid replacement therapy, and, in patients with CD, may be complicated by corticotroph tumor progression syndrome in 25–40% of patients[
14].
After successful surgery for CS, the rapid onset of adrenal insufficiency (AI) is anticipated and usually portends a favorable prognosis [
15‐
18]; however, despite the use of post-operative corticosteroid replacement, the rapid reduction in cortisol exposure often results in an enigmatic phenomenon referred to as the glucocorticoid withdrawal syndrome (GWS). This article addresses the clinical presentation and the pathogenesis of GWS, as well as its distinction from AI. When available, appropriate references are provided. Statements and guidance provided without references are derived from expert opinion and experience.