Endocrine Abstracts

Establishing failure of trans-sphenoidal surgery (TSS) to cure Cushing’s disease in the immediate post-operative period is essential for early surgical re-exploration. However, there is no consensus regarding the definition of apparent cure. We studied whether the dexamethasone-suppressed corticotrophin-releasing hormone test (LDDST-CRH test) immediately following TSS could accurately identify those with Cushing’s disease requiring further definitive treatment.

The LDDST-CRH test was performed in 25 patients undergoing TSS: 10 with Cushing’s disease and 15 with non-functioning pituitary adenomas (NFAs). For the initial 24 h post-operatively, patients received parenteral hydrocortisone. At 09:00 on day two post-TSS, patients underwent a standard 48 h low dose dexamethasone (DXM) suppression test (LDDST) (0.5 mg DXM 6 hourly) followed by a 9th dose of 0.5 mg DXM and administration of 100 mcg human CRH¹. Serum cortisol of <50 nmol/L following a standard LDDST and <38 nmol/L after a LDDST-CRH test were used as cut-off values to indicate cure of Cushing’s disease. Four out of 10 patients with Cushing’s disease passed the LDDST and LDDST-CRH tests, subsequently showing inadequate cortisol reserve on dynamic testing with no evidence of recurrent disease. Six out of 10 patients with Cushing’s disease showed inadequate cortisol suppression on both LDDST and LDDST-CRH testing, needing immediate further definitive treatment. In those patients with NFAs (no ACTH staining on histology), five passed a standard LDDST, seven failed both a LDDST and LDDST-CRH test and three passed a standard LDDST, but failed a LDDST-CRH test. Follow up of those who failed the LDDST-CRH test showed no clinical or biochemical evidence of hypercortisolism.

In conclusion, the diagnostic accuracy of the LDDST-CRH test in confirming failed cure following TSS is limited by its low specificity and doesn’t confer any additional benefit compared to the use of the standard LDDST post-operatively.

1. Martin NM et al. Comparison of the dexamethasone- suppressed corticotrophin-releasing hormone test and low dose dexamethasone suppression test in the diagnosis of Cushing’s syndrome JCEM 2006 91(7):2582–6