In our case, dynamic biochemical tests were discordant since (a) the suppression of serum cortisol in high-dose dexamethasone test was >50% from baseline suggesting CD, (b) the increase in serum cortisol and plasma ACTH after CRH stimulation was less than 20% and 35%, respectively, and (c) there was no pituitary lesion and no central-to-peripheral gradient on BIPSS
, both suggesting ECS.
So, BIPSS was performed to confirm CD and to ensure lateralization of the pituitary adenoma, either.
Since BIPSS was introduced more than 20 years ago, it has become a widely used technique as a part of the diagnostic tests in CS (12,13).
False-negative results in BIPSS may be attributed to anatomical venous malformations such as an atrophic inferior petrosal sinus (19).
False-positive results may occur in BIPSS when the serum cortisol levels are not high enough to suppress the corticotroph cells in cases of cyclic or mild CS and periodic hormonogenesis from ectopic sources (22,23).
Although the patient had an adenoma on the right side of the pituitary on MRI, the BIPSS revealed lateralization to the left side of the pituitary.