Limited Invasive Protocol: Optimizing Diagnostic Modalities in Corticotropin Mediated Cushing Syndrome

To limit the role of bilateral inferior petrosal sinus sampling (BIPSS) in distinguishing between Cushing disease (CD) and ectopic Cushing syndrome (ECS), recent reports have proposed a noninvasive approach based on a combination of biochemical testing and radiological imaging as an alternative to the conventional invasive strategy (CIS). However, this strategy requires further validation. The current study aimed to evaluate 2 limited invasive protocols (LIP-1 and LIP-2) in limiting the role of BIPSS while maintaining a diagnostic accuracy similar to that of CIS.

This was a single-center study conducted on individuals with corticotropin-dependent Cushing syndrome. The LIPs were based on performing high-dose dexamethasone suppression (>50% cut-off in first [LIP-1] and >80% in second [LIP-2]) and magnetic resonance imaging of the sella in all individuals and selective use of computed tomography of the chest and abdomen before BIPSS. These LIPs were evaluated for limiting the use of BIPSS, their accuracy, and cost in comparison to CIS.

Of the 206 individuals, 114 (97 of CD and 21 of ECS) were eligible for the current study. Using LIP-1, LIP-2, and CIS, BIPSS could have been avoided in 62.3%, 35.9%, and 25.4% of individuals, respectively. The positive predictive value for CD using LIP-1 and LIP-2 was 98.9% and 100%, respectively. The cost per patient evaluated using LIP-1, LIP-2, and CIS was $602.21, $966.81, and $1107.78, respectively.

LIPs represent an equally accurate, less invasive, and more cost-effective alternative to the CIS for distinguishing between CD and ECS.