"Cyclical Cushing's syndrome is a pattern of hypercortisolism in which the biochemistry of cortisol production fluctuates rhythmically. This syndrome is often associated with fluctuating symptoms and signs. This type of case was initially thought to be rare. It has, however, recently been recognized as occurring much more frequently. The phenomenon is important because it can, if not recognized, lead to errors in diagnosis and differential diagnosis of the syndrome and in assessment of therapeutic outcomes. All of these can have very serious clinical consequences."
Dr. Friedman, et al, in High Prevalence of Normal Tests Assessing Hypercortisolism in Subjects with Mild and Episodic Cushing’s Syndrome Suggests that the Paradigm for Diagnosis and Exclusion of Cushing’s Syndrome Requires Multiple Testing
"Periodic or cyclical Cushing’s syndrome refers to elevated cortisol levels present at regular intervals, while episodic Cushing’s syndrome refers to elevated cortisol levels occurring without any temporal pattern. A recent review article suggested that cyclic cortisol production is present in about 20–40 % of patients with Cushing’s syndrome ."Cyclical Cushing's is not understood by many endocrinologists. It was once a controversial condition not accepted by many. However, in recent years, the research has given an acknowledgement of the condition. Dr, Friedman's research, linked above, says, "mild hypercortisolism may be quite devastating to the patient. Thus, we cannot advocate a “tincture of time” approach." This article goes on to recommend multiple, repeat testing for cyclical Cushing's because of the increased variability of cortisol levels. Many endocrinologists do one or two tests (or none at all) and determine evidence of hypercortisolism from that, rather than testing for cyclical Cushing's.