Endocrine Abstracts

Objective: Inferior petrosal sinus sampling (IPSS) with CRH stimulation is considered the gold standard for the differential diagnosis of ACTH-dependent Cushing’s syndrome. The aim of this study is to evaluate its role in confirmation and lateralisation of a pituitary source in suspected Cushing’s disease (CD).

Methodology: Nine patients with CD with indeterminate MRI underwent IPSS from August 2004 to February 2007. Three were being assessed for recurrent disease. The following parameters were evaluated: i) Central- to- Peripheral ACTH gradient for localisation, ii) Inter-petrosal sinus gradients for lateralisation, iii) Surgical histopathology, and iv) Post-operative clinical course.

Results: A Central- to- Peripheral ACTH gradient of ≥2.0 was found in 7/9 patients at base line and a gradient of ≥3.0 in all patients after CRH stimulation, confirming pituitary source of ACTH excess. Inter-petrosal sinus gradient of ≥1.4 was observed in 8/9 patients at base line and in all patients after CRH stimulation. This correlated with lateralisation of the excess ACTH source in all patients undergoing their first resection resulting in remission. For recurrent CD patients, the site of resection was made intra-operatively based on macroscopic appearance and frozen section. The IPSS lateralisation did not appear to have influenced the decision. Two had pituitary adenoma confirmed, however all three did not achieve remission.

Conclusion: IPSS can help confirm the location and even lateralise the source of ACTH production. In patients undergoing their first resection, the results are useful to direct surgeons to the appropriate site of excision (100% sensitivity and specificity). For patients with recurrent disease, IPSS was useful in confirming the source of excess ACTH. However, its role in determining and guiding the site of surgical excision still warrants further investigation.