Purpose of review: This article reviews the features of cyclical hypercortisolism. This syndrome was once considered to be very rare but is now being increasingly recognized.
Recent findings: Either true cycles or the variant of episodic and fluctuating levels of hypercortisolism can lead to considerable clinical dilemmas, which are discussed. The review details possible pathophysiological mechanisms and the effects of centrally acting drugs.
Summary: 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. Clinical researchers, including ourselves, have developed criteria, protocols and dynamic biochemical tools to detect cycling in patients with hypercortisolism. Unfortunately, the mechanisms causing the abnormal pathophysiology have not been well elucidated but some recent insights have been gained. The review discusses strategies for diagnosing and managing this important subgroup of patients with hypercortisolism.