Cushing's syndrome is most frequently seen in patients on exogenous glucocorticoids (ie, steroids) for immune-related conditions (eg, rheumatoid arthritis and asthma) and specific haematological cancers. Endogenous Cushing's syndrome is rare, with the excess glucocorticoids arising from the adrenal cortex. The majority of cases are adrenocorticotropic hormone (ACTH)-dependent, most often pituitary-dependent Cushing's syndrome (Cushing's disease), which was first described by Harvey Cushing in 1932. 1 These are generally small corticotroph tumours, although 5–10% are macroadenomas. Over the past 2 years, an increasing proportion of ACTH-dependent Cushing's syndrome has been identified as arising from neuroendocrine tumours, causing ectopic ACTH syndrome, many from small bronchial carcinoids. For ACTH-independent Cushing's syndrome, these could be due to adrenal adenomas or carcinomas, as well as rare bilateral micronodular or macronodular adrenal hyperplasia. 2
Ashley Grossman (Sun,) studied this question.