MON-LB51 Stimulation for Bilateral Inferior Petrosal Sinus Sampling May Be Unnecessary for Diagnosis of ACTH Dependent Cushing Syndrome

Introduction: Bilateral inferior petrosal sinus sampling (BIPSS) is the gold standard test to differentiate Cushing’s disease (CD) and ectopic ACTH syndrome (EAS). Stimulation test for diagnosis may be unnecessary in some cases and the diagnostic yield of the stimulation test may be similar to the basal measurement. Methods: 34 adult patients referred for diagnosis of ACTH dependent Cushing syndrome. Basal simples for prolactin and ACTH were taken from bilateral inferior petrosal sinus and from peripheral vein. Stimulation test with desmopressin (32 subject) or CRH (2 subjects) was performed. Samples were taken at 0, 3, 5 and 10 minutes. To compare the percentage of diagnosis with each measurement the MacNemar test was done. Results: Right basal ACTH was 465 pg./ml (ICR 62-1250), ACTH at 3 minutes was 647 (ICR 227-2610), ACTH at 5 minutes was 1250 (ICR 245-1965), ACTH at 10 minutes was 230 (71-550). Left basal ACTH was 230 (71-550), at 3 minutes was 453 (ICR 116-1250), at 5 minutes was 431 (91-1250), at 10 minutes was 534 (140-1250). Median basal ACTH ratio was 13.8 (ICR 5.1-26), at 3 minutes was 34.5 (ICR 13-82), at 5 minutes was 30.6 (11.4-49.8), at 10 minutes was 18.5 (8.2-48.2). The higher ratio was at 3 minutes. Basal ACTH ratio was <2 in only 4 cases. 2 out of 4 cases had ratio >3 after stimulation test. CD was diagnosed with basal ratio in 88.6% of cases, and at 3, 5 and 10 minutes in 94.3% of cases. There was no difference in percentage of CD diagnosis at 3, 5 or 10 minutes (p=1.0). Discussion: Basal ACTH ratio was able to differentiate CD from ECS in most cases (88.6%). At least one additional sample with CRH or desmopressin stimuli identify 94.3% of CD cases with the higher increases at 3 minutes. Additional stimuli do not improve overall diagnosis, therefore, a basal ratio and additional stimulation test at 3 minutes is enough for CD diagnosis. This may decrease the cost of BIPSS and total duration of the procedure.