Women are more affected with Cushing syndrome than men, at a ratio of 4:1. This is often because of Cushing disease, due to pituitary adenoma.
Exogenous administration of glucocorticoids can results in iatrogenic Cushing syndrome, which is the most common cause of Cushing syndrome.
Of the endogenous causes of Cushing Syndrome, decreased ACTH occurs due to primary adrenal issues. ACTH is low due to negative feedback from increased corticoids.
This can be either adrenal hyperplasia, adenoma or carcinoma. It is characterized by hypercortisolism, due to secretion from the adrenals, and low ACTH. As these are 1° adrenal disorders, cortisol secretion is always elevated and does not respond to high or low-dose dexomethasone suppression tests.
Of the endogenous causes of Cushing Syndrome, increased ACTH levels point to a diagnosis of either an ACTH-secreting pituitary adenoma (Cushing Disease) or paraneoplastic ACTH secretion.
This is the most common cause of endogenous Cushing syndrome. It is usually due to a ACTH-producing pituitary micro adenoma. This presentation, involving the pituitary, is known as Cushing Disease.
Small cell carcinoma of the lung, in a paraneoplastic manner, can secrete ACTH. This subsequently yields high cortisol levels, which are not suppressed by low or high dose dexamethasone suppression tests.
This is a rare cause of Cushing syndrome that can result in pituitary hyperplasia and increased ACTH secretion.
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