Cushing’s (or high cortisol levels) is an unusual disease with a calculated incidence of 1 case/100,000-500,000 population. The two main causes of high cortisol are either related to a pituitary tumor versus an adrenal gland tumor. High cortisol secondary to pituitary tumor (60-70% of patients) is called Cushing’s disease. High cortisol related to an adrenal tumor is called Cushing’s syndrome. Even though frank Cushing’s syndrome is rare, the widespread use of abdominal imaging techniques such as CT scan or MRI has resulted in more incidental adrenal tumors being detected. Blood testing frequently shows that they have high cortisol production (between 5-20% of patients) with a calculated prevalence of about 78 cases/100,000 population. Thus, this condition is much more common than Cushing’s disease. These patients with subclinical Cushing’s have a higher incidence of high blood pressure, obesity and of diabetes mellitus than the general population although they do not have the classical clinical features of Cushing’s. Full blown clinical Cushing’s has very characteristic clinical features including weight gain, fat accumulation in the face (moon facies), buffalo hump, excessive hair growth (hirsutism), acne and increased pigmentation (in Cushing’s disease).
Although high blood pressure is common among all patients with Cushing’s, irrespective of the cause, in the case of Cushing’s related to the use of cortisol pills (for asthma or allergies) the prevalence of high blood pressure is less common, only about 20% of patients. The severity of the high blood pressure in Cushing’s tends to be mild.
For patients in whom Cushing’s is suspected, a 24-hour collection for urinary free cortisol is the best screening test. If this test is not suggestive, a bedtime salivary cortisol measurement can be done. For patients in whom an adrenal tumor is found incidentally while they are getting a CT scan of the abdomen, the best screening test is an overnight dexamethasone suppression test in which 1 mg of dexamethasone is administered at 11 p.m. and a cortisol level is measured the next morning at 8 a.m. If biochemical testing suggest an adrenal tumor, at CT scan or MRI of the abdomen is used localize the tumor to the left or right adrenal gland.
For patients with Cushing’s from a pituitary tumor, the treatment usually consists of surgery and medication. For patients with an adrenal tumor causing Cushing’s, the treatment is to remove the affected adrenal gland. The recommended approach is a laparoscopic adrenalectomy and is 90% effective. This surgery is offered through the Adrenal Center at Georgia Regents Medical Center.