Clinicians who have never missed the diagnosis of Cushing's syndrome or have never been fooled by attempting to establish its cause should refer their patients with suspected hypercortisolism to someone who has. This quote, by Professor James Findling, an expert in Cushings syndrome, is a reminder of the difficulties in diagnosing Cushings syndrome. These difficulties in part reflect the increasing incidence of obesity, hypertension and type 2 diabetes. We will be asked to exclude Cushings syndrome in individuals who have these diagnoses but do not have hypercortisolism. Similarly, there is no clinical sign or biochemical investigation for Cushings syndrome which has perfect diagnostic accuracy.
Importantly, we can do harm in misdiagnosing Cushings syndrome. If we delay diagnosis, the patient could experience the negative effects of excess cortisol. However, perhaps more significantly, a diagnosis of Cushings syndrome will almost inevitably result in surgery for most patients, so we need to be sure that the patient really has Cushings syndrome.
The 2008 Endocrine Society Clinical Practice Guidelines recommend three first-line investigations for the diagnosis of Cushing's syndrome and these exploit different aspects of cortisol excess; late night salivary cortisol measurement, dexamethasone suppression testing and 24-hour urine free cortisol measurement. This talk will review the accuracy of these investigations and will explore how to proceed when the clinical suspicion of Cushings syndrome and the results of these investigations dont match up.