Management of diabetes mellitus in Cushing's syndrome

Active Cushing's syndrome is associated with insulin resistance induced by the high and prolonged circulating level of glucocorticoids. In endogenous Cushing's syndrome the overall incidence of diabetes mellitus and insulin resistance is very likely to be under-reported as not all patients are actively investigated with glucose tolerance tests. Whilst it is common clinical experience that management of diabetes mellitus is necessary in patients with Cushing's syndrome there is a dearth of literature-based evidence to support which regimes are the most effective. Therefore, a pragmatic approach is necessary on an individualized patient basis, whereby patients are stratified according to the severity of their impaired glucose homeostasis. The most effective means of control of diabetes mellitus in a patient with active Cushing's syndrome is to lower the levels of circulating cortisol. This may initially be achieved by using adrenal steroidogenesis blockade with drugs including metyrapone, ketaconazole, or, on occasion, mitotane. The rapid action of metyrapone is particularly suitable in this circumstance. Despite this, diabetes-specific therapy is often necessary and metformin and PPAR-γ agonists may be of use, but in the acute setting insulin therapy is frequently needed. Definitive management directed against source driving Cushing's syndrome is often highly effective at either reducing the severity of diabetes, or allowing its complete resolution. Patients experiencing diabetes mellitus in the context of exogenously administered glucocorticoids may well require insulin therapy for the period that the high levels of steroids are being administered. Despite resolution of Cushing's syndrome after definitive treatment patients may continue to exhibit insulin resistance. This and other cardiovascular risk factors require ongoing and long-term attention.