Standalone Outpatient CRH Testing Before BIPSS in ACTH-Dependent Cushing's Syndrome
No, a standalone outpatient CRH stimulation test is not necessary before performing Bilateral Inferior Petrosal Sinus Sampling (BIPSS) in patients with ACTH-dependent Cushing's syndrome. 1, 2
Diagnostic Approach to ACTH-Dependent Cushing's Syndrome
- ACTH-dependent Cushing's syndrome should first be confirmed by measuring ACTH levels, with levels >5 ng/L (>1.1 pmol/L) indicating ACTH dependency 1, 3
- A cut-off value of 29 ng/L (6.4 pmol/L) for ACTH has 70% sensitivity and 100% specificity for diagnosing Cushing's disease 1, 3
- After confirming ACTH dependency, pituitary MRI should be performed to identify a potential adenoma 2, 4
Role of BIPSS in Diagnosis
- BIPSS is indicated when ACTH-dependent Cushing's syndrome is confirmed but no adenoma is identified on pituitary MRI 1, 2
- BIPSS is considered the gold standard for differentiating between pituitary and ectopic sources of ACTH excess 2, 5
- BIPSS should only be performed in specialized centers with experienced interventional radiologists 1
CRH Stimulation During BIPSS
- CRH stimulation is administered during the BIPSS procedure itself, not as a separate outpatient test beforehand 1, 2
- During BIPSS, a pituitary source of ACTH excess is confirmed by:
- CRH stimulation during BIPSS significantly improves diagnostic accuracy compared to unstimulated sampling 2, 5
Important Procedural Considerations
- Hypercortisolemia should be confirmed immediately prior to BIPSS to ensure the patient is in an active disease phase, especially important for cyclical Cushing's disease 1, 2
- Medical therapy for Cushing's disease (steroidogenesis inhibitors) must be stopped before BIPSS to enable accurate interpretation of results 1
- Either CRH or desmopressin can be used as stimulants during BIPSS with similar accuracy 1
Additional Benefits of BIPSS
- BIPSS may help lateralize the pituitary adenoma when no lesion is visible on MRI 1
- Lateralization is suggested by an inter-petrosal sinus ACTH gradient ≥1.4 between the two sides after CRH stimulation 1
- Lateralization accuracy varies, with studies showing 58-91% concordance with surgical findings 1, 2
Common Pitfalls to Avoid
- Performing BIPSS without first confirming ACTH-dependent Cushing's syndrome biochemically 2, 4
- Conducting BIPSS during a period of cyclic remission in patients with cyclical Cushing's disease 1, 2
- Relying solely on BIPSS lateralization data for surgical planning, as false lateralization can occur due to altered pituitary blood flow 1, 2