OCCULT EUTOPIC CUSHINGS-SYNDROME - FAILURE OF SIMULTANEOUS BILATERAL PETROSAL SINUS SAMPLING TO DIAGNOSE PITUITARY-DEPENDENT CUSHINGS-SYNDROME

Simultaneous bilateral inferior petrosal sinus (LPS) sampling has been repeatedly proposed to be a highly specific approach for the diagnosi s of Gushing's disease and 100% sensitivity in detecting autonomous pi tuitary ACTH secretion by an adenoma has been reported in a large seri es. We new report on a patient suffering from ACTH-dependent Gushing's syndrome in whom repeated bilateral IFS sampling failed to detect a c entral/peripheral gradient diagnostic for autonomous pituitary ACTH se cretion during initial evaluation. Applying lysine vasopressin as the corticotroph secretatogue, the maximum central/peripheral gradient was 1.0 before and 1.1 following stimulation. Moreover, results of high d ose dexamethasone and corticotrophin releasing hormone administration suggested ectopic ACTH secretion. Since thorough diagnostic procedures failed to localise a suspected carcinoid tumour, occult ectopic Gushi ng's syndrome was diagnosed. Eight years later, a pituitary macroadeno ma was detected by magnetic resonance imaging (MRI). IFS catheterisati on then revealed a maximal central/peripheral gradient of 9.3 before a nd 20.4 after the intravenous administration of lysine vasopressin. Re sected tumour tissue was classified as a typical densely granulated AC TH cell adenoma. We conclude that repeated MRI scans should be include d in the follow-up of patients with a diagnosis of occult ectopic Gush ing's syndrome to avoid the risk of overlooking 'occult eutopic Gushin g's syndrome'.