What is the main cause of Cushing's syndrome?

The main cause of Cushing's syndrome is the presence of excessive levels of cortisol in the body. Cushing's syndrome can arise from various conditions that lead to elevated cortisol, which is a steroid hormone produced primarily by the adrenal glands. This can occur due to a tumor in the pituitary gland causing overproduction of adrenocorticotropic hormone (ACTH), which in turn stimulates cortisol production from the adrenal glands. It can also result from adrenal tumors or from prolonged use of corticosteroid medications.

In contrast, insufficient thyroid hormone production and deficiencies in growth hormone relate to different endocrine disorders, such as hypothyroidism and growth hormone deficiency, respectively. Low levels of insulin pertain to diabetes and metabolic disorders, which are unrelated to Cushing's syndrome. Thus, the correlation of Cushing's syndrome with excessive cortisol underscores its primary cause.