Pitfalls in the Use of Inferior Petrosal Sinus Sampling for the Differential Diagnosis of ACTH-Dependent Cushingʼs Syndrome

Inferior petrosal sinus sampling is highly accurate in distinguishing pituitary from ectopic sources of ACTH in Cushing's syndrome. However, this test may give misleading results in several clinical situations. These include patients in whom hypercortisolism is the result of a pseudo-Cushing state, patients who have ACTH-independent Cushing's syndrome, patients with episodic or mild hypercortisolism that is insufficient to suppress ACTH secretion of the normal pituitary corticotrophs, and patients who have disparate results between inferior petrosal sinus sampling and the noninvasive tests used to distinguish Cushing's disease from the ectopic ACTH syndrome. Due to these limitations, petrosal sinus sampling should be reserved for patients with clear clinical and biochemical evidence of ACTH-dependent Cushing's syndrome, and must be interpreted cautiously whenever the results conflict with those of the noninvasive tests of differential diagnosis.