Episodic hypercortisolemia-mediated periods of worsening hyperglycemia in cyclic Cushing syndrome.

Cyclic Cushing syndrome (CCS) is a rare subtype of Cushing syndrome (CS) characterized by hypercortisolism alternating with periods of physiologic or even low cortisol secretion. Most patients with CCS present with clinical signs of CS; however, in some patients, signs of hypercortisolism may be subtle or even absent. The fluctuating clinical picture and discrepant biochemical findings make CCS difficult to diagnose. We describe a case of a 70-year-old man with well-controlled type 2 diabetes mellitus who experienced recurrent, spontaneous hypercortisolemic episodes resulting in worsening and difficult-to-control hyperglycemia, followed by eucortisolemic phases during which his glycemic control rapidly returned to baseline. Further biochemical evaluation revealed intermittent hypercortisolemia without a clearly identifiable source of an adrenocorticotropic hormone secreting lesion. Data from his continuous glucose monitoring system (CGMS) proved pivotal in detecting the hypercortisolemic phases and tailoring management. After declining bilateral adrenalectomy and opting for a block-and-replace regimen with osilodrostat and hydrocortisone, he was able to anticipate and initiate this treatment based on his CGMS readings, facilitating improved glycemic control during these periods. This case highlights the diagnostic complexity of CCS and the utility of CGMS as both a monitoring tool and treatment guide for CCS in patients with concurrent type 2 diabetes mellitus.