Measuring cortisol in Cushing syndrome: diagnosis, monitoring, and cortisol circadian rhythm improvement

Endogenous Cushing syndrome (CS) is a rare disorder resulting from chronic exposure to excessive concentrations of cortisol. It is likely underdiagnosed because many clinical signs and symptoms are non-specific and overlap with those of common conditions. Furthermore, biochemical testing to diagnose CS can be complex and challenging, especially in milder cases. CS is characterized by excessive daily cortisol production, but it is also associated with a disrupted circadian rhythm of cortisol secretion. Traditional cortisol monitoring techniques rely on single-time-point measurements or a cumulation of measurements, which are unable to capture the complete daily rhythm of cortisol fluctuations. Currently, the utility of assessing individual patients' cortisol circadian rhythm during diagnosis and treatment of CS is not well characterized. In this review we will discuss how cortisol is measured in clinical practice and the potential benefit of measurement and normalization of the cortisol circadian rhythm.