IPSS Case Studies

Inferior petrosal sinus sampling differentiates Cushing disease from ectopic adrenocorticotropic hormone secretion using simultaneous petrosal and peripheral venous hormone measurements. A normal pituitary magnetic resonance imaging does not exclude Cushing disease, necessitating sampling. Interpretation relies on central-to-peripheral adrenocorticotropic hormone gradients at baseline and following secretagogues like desmopressin or corticotropin-releasing hormone, utilizing a baseline gradient greater than two or a stimulated gradient greater than three. Concomitant prolactin measurement validates cannulation quality and establishes prolactin-normalized ratios to resolve ambiguous, borderline, or flat gradients, particularly in patients with cyclic hypercortisolism.