Cushing's Disease points specifically to a pituitary source where there is an overproduction of ACTH, however it can still be termed Cushing's Syndrome. All other endogenous sources that are listed below are coined as Cushing's Syndrome, but only a pituitary source gets the name Cushing's Disease.
Information taken from the NIH website.
Pituitary adenomas cause 70 percent of Cushing's syndrome cases,1 excluding those caused by glucocorticoid use. These benign, or noncancerous, tumors of the pituitary gland secrete extra ACTH. Most people with the disorder have a single adenoma. This form of the syndrome, known as Cushing's disease, affects women five times more often than men.
Ectopic ACTH Syndrome
Some benign or, more often, cancerous tumors that arise outside the pituitary can produce ACTH. This condition is known as ectopic ACTH syndrome. Lung tumors cause more than half of these cases, and men are affected three times more often than women. The most common forms of ACTH-producing tumors are small cell lung cancer, which accounts for about 13 percent of all lung cancer cases,2 and carcinoid tumors-small, slow-growing tumors that arise from hormone-producing cells in various parts of the body. Other less common types of tumors that can produce ACTH are thymomas, pancreatic islet cell tumors, and medullary carcinomas of the thyroid.
In rare cases, an abnormality of the adrenal glands, most often an adrenal tumor, causes Cushing's syndrome. Adrenal tumors are four to five times more common in women than men, and the average age of onset is about 40. Most of these cases involve noncancerous tumors of adrenal tissue called adrenal adenomas, which release excess cortisol into the blood.
Adrenocortical carcinomas-adrenal cancers-are the least common cause of Cushing's syndrome. With adrenocortical carcinomas, cancer cells secrete excess levels of several adrenocortical hormones, including cortisol and adrenal androgens, a type of male hormone. Adrenocortical carcinomas usually cause very high hormone levels and rapid development of symptoms.
Familial Cushing's Syndrome
Most cases of Cushing's syndrome are not inherited. Rarely, however, Cushing's syndrome results from an inherited tendency to develop tumors of one or more endocrine glands. Endocrine glands release hormones into the bloodstream. With primary pigmented micronodular adrenal disease, children or young adults develop small cortisol-producing tumors of the adrenal glands. With multiple endocrine neoplasia type 1 (MEN1), hormone-secreting tumors of the parathyroid glands, pancreas, and pituitary develop; Cushing's syndrome in MEN1 may be due to pituitary, ectopic, or adrenal tumors.
1Nieman LK, Ilias I. Evaluation and treatment of Cushing’s syndrome. The Journal of American Medicine. 2005;118(12):1340-1346.
2Govindan R, Page N, Morgensztern D, et al. Changing epidemiology of small-cell lung cancer in the United States over the last 30 years: analysis of the surveillance, epidemiologic, and end results database. Journal of Clinical Oncology. 2006;24:4539-4544.
Endogenous versus Exogenous: Endogenous means produced or growing from within. Exogenous means originating or produced outside of the body.
There is also the most common type of Cushing's Syndrome which is the exogenous form and it's called Iatrogenic Cushing's Syndrome. This type of Cushing's is caused by glucocorticoids that are prescribed by a physician for other diseases or ailments. People who suffer from allergies, asthma and even organ transplant recipients who need to keep their immune systems suppressed need these type of steroids in order to function, but it can come with the cost of developing this form of Cushing's Syndrome. Usually tapering or lowering the dose will alleviate all symptoms, but for some it may not be an option to get off of the steroids.
In the Cushing's community we usually refer to this type as steroid induced Cushing's.
There is even something called Pseudo-Cushing's Syndrome.
"Pseudo-Cushing syndromes are a heterogeneous group of disorders, including alcoholism, anorexia nervosa, visceral obesity, and depression, which share many of the clinical and biochemical features of Cushing's syndrome. The mechanisms responsible for the genesis of pseudo-Cushing's syndrome are poorly understood. It has been suggested that hypercortisolism of pseudo-Cushing syndrome may be the result of increased hypothalamic corticotrophin-releasing hormone (CRH) secretion in the context of a hypothalamic-pituitary-adrenal axis that is otherwise normally constituted. The substantial overlap in clinical and biochemical features among several patients with Cushing syndrome and those with pseudo-Cushing syndromes can make the differential diagnosis difficult. Distinguishing between pseudo-Cushing's syndrome and true Cushing's syndrome is critical for preventing the unnecessary and potentially harmful treatment of such patients. This brief review summarizes the main pathophysiological events of pseudo-Cushing syndromes and provides a useful strategy for differential diagnosis."
Pseudo-Cushing's Syndrome is explained in great detail in this PDF on Dr. Friedman's website.
Feeling confused? Imagine all the testing necessary to determine which type you specifically have.