Diagnosing Cushing's disease in the context of chronic kidney disease: a case report and literature review.

Objective: The diagnosis of Cushing's disease (CD) is particularly challenging in patients with chronic kidney disease (CKD) due to abnormalities of the hypothalamo-pituitary-adrenal axis associated with the latter. This case report presents discrepant biochemical findings in a patient with CKD who was subsequently diagnosed with CD, and outlines principles which may guide the definitive diagnosis of CD in this context.

Methods: The case of a patient with Stage 4 CKD who underwent transsphenoidal surgery for pituitary-dependent CD is presented. A literature review was conducted to identify similar cases and characterise features of hypothalamo-pituitary-adrenal axis dysfunction in CKD.

Results: The patient discussed herein presented with markedly elevated plasma adrenocorticotrophic hormone (ACTH) due to a pituitary macroadenoma, with normal 24-h urine free cortisol (24-UFC) but abnormal overnight dexamethasone suppression testing and elevated midnight salivary cortisol. He experienced biochemical remission after undergoing transsphenoidal adenomectomy. A literature review revealed that CKD can be associated with elevated serum cortisol, reduced UFC and elevated plasma ACTH. Only four other cases of CD being diagnosed in a patient with CKD have been published. The loss of a circadian rhythm of cortisol secretion was the most common feature among all cases.

Conclusions: To establish a definitive diagnosis of CD in the context of pre-existing CKD, the absence of circadian rhythms of cortisol and ACTH is a more sensitive indicator than 24-UFC and low-dose dexamethasone suppression testing.