Endocrine Abstracts

‘Silent’ ACTH-secreting pituitary adenomas are not characterized by specific clinical features that would suggest the presence of hypercortisolism. In contrast, they present as non-functioning pituitary macroadenomas with either visual compromise or hypercortisolism. However, immunostaining reveals ACTH-secreting cells.

In order to characterize the laboratory features of these tumours, we have preoperatively assessed 56 patients with either clinically non-functioning pituitary adenomas or Cushing’s disease with a standardized protocol. They had plasma measurements of cortisol and ACTH, low-dose (2 mg) dexamethasone testing and 24-hour urine corticosteroid determinations. All tumour specimen underwent immunohistochemistry. We compared the laboratory findings in ‘silent’ ACTH-secreting (SACTH; n=6) and ‘silent’ gonadotropin-secreting (SGON, n=14) tumours to those who did not immunostain for any hormone (INACT, n=22) and patients with Cushing’s disease (CD, n=13).

Mean plasma cortisol varied from 555.8 nmol/l in patients with CD, 358.3 nmol/l in patients with SACTH, 389.6 nmol/l in patients with SGON and 409.3 nmol/l in patients with INACT. In contrast, mean plasma ACTH was highest in patients with CD (30.6 pg/ml) and SACTH (22.3 pg/ml), but much lower in patients with SGON (14.2 pg/ml) and in INACT (12.3 pg/ml). Likewise, mean dexamethason-suppressed cortisol levels were much lower in patients with SGON (49.7 nmol/l) and INACT (48.7 nmol/l) than in patients with SACTH (216.2 nmol/l) and of course, those with CD (441.5 nmol/l). While all mean steroid hormones in the 24-hour-urines of patients with CD were clearly elevated, there was no significant difference in the urine steroids between patients with SACTH, SGON and INACT. Mean free urinary 24-hour-cortisol was 304.8 μg in CD, 38.7 μg in SACTH, 70.5 μg in SGON and 44.2. μg INACT.

We thus conclude, that biochemistry allow us to preoperatively different-tiate the subtypes of ‘non-functioning’ pituitary adenomas. However, plasma ACTH-levels and dexamethasone suppression testing in this context seem to be superior to urine steroid measurements.