1: J Neurosurg  1995 Dec;83(6):1087-91 

False-positive inferior petrosal sinus sampling in the diagnosis of Cushing's
disease. Report of two cases.

Yamamoto Y, Davis DH, Nippoldt TB, Young WF Jr, Huston J 3rd, Parisi JE.

Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, USA.

Inferior petrosal sinus sampling (IPSS) for adrenocorticotropic hormone (ACTH)
levels in patients with Cushing's syndrome has become a useful method to
distinguish ACTH-secreting pituitary tumors (Cushing's disease) from other
causes of the syndrome, principally ectopic adrenocorticotropin secretion by an
occult tumor. Although the test is generally regarded as highly specific, the
authors recently encountered two patients whose IPSS measurements were
false-positive for Cushing's disease. The results of IPSS suggested a pituitary
origin of ACTH secretion in both patients, but transsphenoidal surgery failed to
disclose a pituitary adenoma or to improve postoperative plasma cortisol levels.
Both patients subsequently were found to have an ACTH-secreting carcinoid tumor
of the lung. The false-positive IPSS studies were due to periodic
hormonogenesis. The patients must be hypercortisolemic at the time IPSS is
performed for the study to be valid.

PMID: 7490627 [PubMed - indexed for MEDLINE]