Question: What is pseudo-Cushing’s?
Answer: Pseudo-Cushing’s refers to individuals who have biochemical abnormalities or physical manifestations which are similar to Cushing’s syndrome; abnormal production rates of cortisol and abnormal feedback inhibition by glucocorticoids like dexamethasone are also present. There are several common causes of pseudo-Cushing’s. One that has been clearly described occurs in patients with severe endogenous depression. These patients can have increased cortisol production rates as measured in 24 hr urines and abnormal suppression of cortisol and ACTH with a dexamethasone suppression test. The test results can be very similar to those in pituitary Cushing’s disease; however, in most cases, these patients do not have the physical features of Cushing’s syndrome.
The second most common situation which can lead to excess cortisol production is excessive alcohol consumption. This can reproduce the same biochemical abnormalities of excess cortisol production and is often accompanied by central obesity with supraclavicular fat pads, and a red, round face. Alcohol-induced elevation of cortisol can be distinguished from other causes by the fact that when alcohol consumption is ceased, the biochemical abnormalities usually return to normal within a few days.
Previously, differentiation between some types of pseudo-Cushing’s and Cushing’s syndrome could be difficult. Recently, the NIH group has described a new combined dexamethasone/CRH test which discriminates between endogenous Cushing’s syndrome and pseudo-Cushing’s syndrome with close to a 100 % accuracy. Dexamethasone is given at 0.5 mg every 6 hrs. for 48 hours and two hours after the last dose, CRH is administered at the dose of 1ug/kg of body weight, intravenously; plasma cortisol is measured 15 minutes later. In endogenous Cushing’s syndrome cortisol levels are elevated at the 15 minute time point, whereas in pseudo-Cushing’s syndrome, the levels of cortisol are below 1.4 mcg/dl at the 15 minute time point.
There are other conditions that tend to increase cortisol production. Some of them are eating disorders like anorexia nervosa, or chronic illness such as AIDS. These patients can fail to suppress with dexamethasone and in most cases do not display the physical manifestations of Cushing’s syndrome.
By Dr. Andre Lacroix MD (Fall, 1997)