By Sherry Boschert, Clinical Endocrinology News Digital Network
SAN FRANCISCO – Measurements of prolactin levels during inferior petrosal sinus sampling did not help localize pituitary adenomas in patients with Cushing's disease in a study of 28 patients, contradicting findings from a previous study of 28 patients.
The value of prolactin measurements in tumor localization using inferior petrosal sinus sampling (IPSS) remains unclear and needs further study in a larger, prospective study, Dr. Susmeeta T. Sharma said at the Endocrine Society's Annual Meeting. The current and previous studies were retrospective analyses.
Although IPSS has been considered the standard test in patients with ACTH-dependent Cushing's syndrome to differentiate between ectopic ACTH secretion and Cushing's disease, there has been controversy about its value in localizing adenomas within the pituitary gland once a biochemical diagnosis of Cushing's disease has been made. Various studies that used an intersinus ACTH ratio of 1.4 or greater before or after corticotropin-releasing hormone (CRH) stimulation have reported success rates as low as 50% and as high as 100% for tumor location.
A previous retrospective study of 28 patients with Cushing's disease reported that adjusting the ACTH intersinus gradient by levels of prolactin before or after CRH stimulation, and combining the prolactin-adjusted ACTH intersinus ratio, improved pituitary adenoma localization. Magnetic resonance imaging (MRI) alone correctly localized the pituitary adenoma in 17 patients (61%), a prolactin-adjusted ACTH intersinus ratio of at least 1.4 improved the localization rate to 21 patients (75%), and combining MRI and the prolactin-adjusted ACTH intersinus ratio improved localization further to 23 patients, or 82% (Clin. Endocrinol. 2012;77:268-74).
The findings inspired the current retrospective study. The investigators looked at prolactin levels measured in stored petrosal and peripheral venous samples at baseline and at the time of peak ACTH levels after CRH stimulation for 28 patients with Cushing's disease and ACTH-positive pituitary adenomas who underwent IPSS in 2007-2013. The investigators calculated prolactin-adjusted values by dividing each ACTH value by the concomitant ipsilateral prolactin value. They used an intersinus ACTH ratio of 1.4 or greater to predict tumor location.
At surgery, 26 patients had a single lateral tumor (meaning its epicenter was not in the midline), 1 patient had a central microadenoma, and 1 patient had a macroadenoma, reported Dr. Sharma of the National Institute of Child Health and Human Development, Bethesda, Md.
MRI findings accurately identified the location of 21 of the 26 lateral tumors (81%), compared with accurate localization in 18 patients using either the unadjusted ACTH intersinus ratio or the prolactin-adjusted ACTH intersinus ratio (69% for each), she said.
Incorrect tumor localization occurred with one patient using MRI alone and seven patients using either ratio. In four patients whose tumors could not be localized by MRI, the uncorrected and prolactin-adjusted ratios localized one tumor correctly and three tumors incorrectly. Only MRI correctly localized the one central microadenoma.
"We did not find any difference in localization rates by measurement of prolactin during IPSS," she said. The small size of the study and its retrospective design invite further research in a more robust study.
Dr. Sharma reported having no financial disclosures.