THU039 Use Of Desmopressin In The Differential Diagnosis Of Cushing’s Syndrome: Recent Experience At The NIH
Authors: McGlotten Raven , Nieman Lynnette K 
Published: October 2023

Abstract
Disclosure: R. McGlotten: None. L.K. Nieman: None.
Background: Stimulation (stim) testing and petrosal sinus sampling (PSS) help determine the etiology of ACTH-dependent Cushing's syndrome (CS). As CRH is not available in the US, desmopressin (Desmo) is an alternative agent for both purposes. For the peripheral Desmo stim test, the reported sensitivity (ACTH:74 - 91%; cortisol (F): 81%) for Cushing's disease (CD) and specificity (ACTH:57-71%; F: 82%) for ectopic ACTH secretion (EAS) vary depending on the timepoints and criteria used for a response. The sensitivity of PSS was ∼ 95-99%. We evaluated our Desmo experience. Methods: We retrospectively reviewed 16 patients (pts) with pathologically-confirmed CS (and one with occult EAS) who underwent PSS (n=6) or Desmo stim testing (all) using a 10 ug IV dose at time 0 minutes (min). Stim test F and ACTH were measured -15, -1, 15, 30, 45, 60, 90, and 120 min. Percent response was calculated according to previous reports using the mean of -15 and 0 min and the mean of 15 and 30 min, or peak, ACTH values and the mean of 30 and 45 min, or peak, F levels. For PSS, ACTH was measured at -5, -1, 3, 5, and 10 min from left and right petrosal veins and a peripheral site. A pre- or post-stimulation gradient between peripheral and PS samples &gt;2 and &gt;3, respectively, was considered to indicate CD. Results: On stim test, positive cortisol responses &gt;20% were found in 9/11 CD pts at 30/45min (range 29-175% vs -35 to 18%) and 10/11 with peak values (range 29 - 184% vs 17%). One of 4 EAS patients had a 30/45 min response (24% vs 6 - 18%) and 3 had a peak response (range 23-51% vs 7%). 9/11 CD patients had &gt;35% ACTH response at 15/30 min (range 73 - 1175%, vs -13%, 7%), while 10/11 had a peak response (range 62 - 1736% vs 18%). However, 2/4 EAS patients had positive 15/30 min response (81%, 324% vs 1, 14%) and 3/4 had positive peak responses (range 44-324% vs 12%), decreasing specificity dramatically. An adrenal adenoma and occult EAS pt did not respond at all. Most CD peak responses were at 15 or 30 min (n=8), with others at 60 and 90 min. EAS peaks were at 0 - 90 min.
6 CD pts underwent PSS; all had a post stimulation PS:peripheral gradient &gt;3 (range 9 - 831). In 4 EAS pts all gradients were &lt;2 (range 1.2-1.4), although one had inadequate cannulation judged by prolactin. There was a good correlation between the 15 min PSS and the 10 min stim test values and type of response except for one CD pt who did not respond on the stim test but increased 362% at PSS. Discussion: Our small sample size showed a robust ACTH and F response to Desmo in nearly all CD but pts with EAS also respond, especially when peak values are used. Diagnostic accuracy was within the range of previous reports. EAS pts with stim test responses did not have a central:peripheral gradient during PSS, confirming an EAS tumor response to Desmo. Thus, negative stim test responses suggest EAS, while positive responses need confirmation by IPSS or other tests. The 120 min stim test values did not contribute to the diagnosis.
Presentation: Thursday, June 15, 2023