Endocrine Abstracts (2008) 16 OC4.5

Comparison of 1-mg versus 8-mg dexamethasone suppression tests (DST) in patients with clinically inapparent adrenal adenoma

Giuseppe Reimondo, Silvia Bovio, Fulvia Daffara, Barbara Allasino, Ilaria Micossi, Barbara Zaggia, Arianna Ardito, Alberto Angeli & Massimo Terzolo

Dipartimento di Scienze Cliniche e Biologiche, Università di Torino, Medicina Interna I, ASO San Luigi, Orbassano (TO), Italy.

Recent guidelines recommend to use the 1-mg DST to screen for subclinical hypercortisolism assuming that a post-DST cortisol >5.0 μg/dl define this condition. However, several experts suggest a more sensitive cut-off at 1.8 μg/dl while others consider mandatory to confirm unsuppressibility with a 8-mg DST. A consecutive series of 64 patients (22 men, 42 women, aged 28–81 years) with clinically inapparent adrenal adenoma were studied between 2005 and 2007. The adrenal masses were discovered serendipitously during diagnostic work-up of non-adrenal diseases and none of the patients presented classic cushingoid features. All the adrenal masses displayed typical CT characteristics of adrenocortical adenoma. The endocrine work-up included: 1-mg DST, 24-h UFC, ACTH, cortisol, midnight serum and salivary cortisol, DHEAS, PRA, aldosterone, urinary fractionated metanephrines. Urinary fractionated metanephrines, PRA and aldosterone resulted in the normal range in all cases. Fifty-two patients (81.2%) did not suppress cortisol <1.8 μg/dl after 1-mg DST (additional alteration of HPA axis in 44.2%) and 11 patients (17.2%) did not suppress <5.0 μg/dl (additional alterations of HPA axis in 63.6%). A subgroup of 22 non-suppressor patients were further investigated with the 8-mg DST. Cortisol levels after 8-mg DST were surprisingly higher than 1-mg DST (4.9±2.2 vs 7.5±4.5 μg/dl, P=0.09). In only 4 patients (18.2%), cortisol levels were lower after 8-mg than 1-mg DST, being <1.8 μg/dl in 2 cases. Even in the 11 patients with cortisol >5.0 μg/dl following 1-mg DST, cortisol levels were higher after 8-mg DST (7.0±1.5 vs 9.6±4.2 μg/dl, P=0.22). These data support the view that secretory autonomy is a common feature of incidental adrenal adenomas. Cortisol is secreted without a complete restrain by pituitary feedback even when the degree of cortisol excess appears to be minimal. Interestingly, greater dexamethasone doses induce paradoxically higher cortisol levels than after 1-mg DST.