The gold standard CRH test is performed using bilateral inferior petrosal sinus sampling (9).
The source of ACTH must be defined; the only way to do this is inferior petrosal sinus ACTH after corticotropin-releasing hormone stimulus.
The patient was referred for inferior petrosal sinus vein sampling, which surprisingly did not show a central to peripheral ACTH gradient.
However, pituitary MRI was negative and inferior petrosal sampling did not show a central to peripheral ACTH gradient.
No adenoma was revealed, but inferior petrosal
sinus sampling showed a central origin.
Bilateral inferior petrosal
sinus sampling of ACTH level is considered the gold standard for differentiating between the two: it is elevated in Cushing's disease but is low or normal in EAS.
The reason for this difference likely lies in the lack of availability in their center of the inferior petrosal sampling (IPSS) test.
Diagnostic errors aider inferior petrosal sinus sampling.
1) The VPVC receives several veins from the endolymphatic sac and drains into the inferior petrosal
sinus or directly into the jugular bulb (figure 4).
Bilateral simultaneous inferior petrosal
sinus sampling (BIPSS) is a highly sensitive but invasive method used in the differential diagnosis of ACTH-dependent CS.
If the source of ACTH cannot be localized conclusively, bilateral inferior petrosal
sinus sampling may be necessary.
sinus sampling (IPSS) was performed only in one patient and confirmed the diagnosis of CD.