FALSE-POSITIVE INFERIOR PETROSAL SINUS SAMPLING IN THE DIAGNOSIS OF CUSHINGS-DISEASE

Inferior petrosal sinus sampling (IPSS) for adrenocorticotropic hormon e (ACTH) levels in patients with Gushing's syndrome has become a usefu l method to distinguish ACTH-secreting pituitary tumors (Gushing's dis ease) from other causes of the syndrome, principally ectopic adrenocor ticotropin secretion by an occult tumor. Although the test is generall y regarded as highly specific, the authors recently encountered two pa tients whose IPSS measurements were false-positive for Cushing's disea se. The results of IPSS suggested a pituitary origin of ACTH secretion in both patients, but transsphenoidal surgery failed to disclose a pi tuitary adenoma or to improve postoperative plasma cortisol levels. Bo th patients subsequently were found to have an ACTH-secreting carcinoi d tumor of the lung. The false-positive IPSS studies were due to perio dic hormonogenesis. The patients must be hypercortisolemic at the time IPSS is performed for the study to be valid.