Letter to the Editor from Piazzola and Castinetti: "Bilateral inferior petrosal sinus sampling with human CRH stimulation in ACTH-dependent Cushing's syndrome: results from a retrospective multicenter study".

This letter addresses the diagnostic utility of bilateral inferior petrosal sinus sampling (BIPSS) with corticotropin-releasing hormone (CRH) stimulation in distinguishing causes of ACTH-dependent Cushing’s syndrome, specifically Cushing’s disease (CD) versus ectopic ACTH secretion (EAS). The authors discuss recent findings showing only modest improvements in sensitivity and specificity with CRH stimulation during BIPSS and highlight challenges due to CRH’s limited availability in Europe and the US. They suggest that basal (unstimulated) BIPSS results, combined with imaging and other dynamic tests such as desmopressin, may be sufficient for diagnosis, noting that stimulation may be necessary only in select cases. The letter calls for further research on comprehensive diagnostic strategies without CRH to guide clinical practice in ACTH-dependent Cushing’s syndrome.