Endocrine Abstracts

The definition of early cure post transphenoidal surgery (TSS) for Cushing’s disease continues to be debated. The low dose dexamethasone suppression test with corticotrophin releasing hormone (LDDST-CRH) is a test for diagnosis of Cushing’s; however it has not been validated in early post TSS to determine remission. The aim of this study was to determine whether the combined LDDST-CRH test could be used in post TSS patients.

The combined LDDST-CRH test was adapted to be used as a standard on all cases of TSS 48 hours post operatively. The patients were put on dexamethasone 0.5 mg 6 hourly starting 48 h postoperatively. A cortisol >50 nM is taken as “failure” of LDDST while a cortisol of >38 nM is taken as failure of CRH testing.

Histological proven cases included 4 Cushing’s (mean age 35 years with 100% females) and 16 non-Cushing’s (mean age 48 years, with 53% females); 7 acromegalics, 8 non-functioning macroadenoma (NFA) and 1 Rathe Cleft Cyst.

Two from four Cushing’s patients passed the combined LDDST-CRH and are currently in remission. The other two failed on both parts of LDDST-CRH, one has been treated with radiotherapy and the other is under review.

Of the seven acromegalics, 6/7 passed the LDDST and 2/7 of the acromegalics failed CRH testing. Of the NFAs 3/8 passed the LDDST and 3/7 who had the CRH testing went on to fail this. The one case of Rathe Cleft Cyst passed the LDDST and failed the CRH testing.

In summary LDDST-CRH testing post TSS in Cushing’s patients was consistent however the test gave 7 false positives in the non-Cushing’s patients who were histological proven not to have Cushing’s disease.

LDDST-CRH testing should not be performed immediately postoperatively in any patients. The addition of CRH causes almost all patients to develop a false positive result postoperatively.