Corticotrophin-releasing factor-test used with bilateral, simultaneous inferior petrosal sinus blood-sampling for the diagnosis of pituitary-dependent Cushing's disease.

Bilateral, simultaneous inferior petrosal sinus blood-sampling for determinations of ACTH levels has improved the ability to establish a differential diagnosis of Cushing's disease, particularly in patients whose endocrinological studies show equivocal results and whose computed tomography scans yield negative or inconclusive findings. Individual anatomical variations in the configuration of the sinus and insignificant differences between the ACTH levels obtained from its two sides may be a problem. Seven patients with clinically and biochemically typical Cushing's disease and one with atypical Cushing's disease were examined. An alternative approach for catheterization of the inferior petrosal sinus through the deep vertebral venous plexus was used in those patients who did not have direct connections between the sinus and the internal jugular vein. In two of the eight patients, only ACTH secretion stimulated with corticotrophin-releasing factor could unmask a significant difference between the ACTH levels on the two sides which was not obvious from the basal ACTH levels. Beta-lipotrophin values showed a behaviour similar to that of ACTH values, but because of a slower turn-over rate, the CRF-induced peaks were better visible. The aetiology of Cushing's disease was established from the results of this examination and corresponded with the surgical findings in this series, with the exception of one in which the patient had a highly atypical form of the disease. The abnormal ACTH source was found later to be a thymus carcinoid.