Pituitary adenoma ACTH secreting

D. Pituitary adenoma that secretes excess ACTH, leading to excess cortisol in the blood. 

D. While all of the choices can lead to hypercortisolism, about two-thirds of all cases are due to a pituitary adenoma that secretes excess ACTH, leading to excess cortisol in the blood. 

The syndrome was first described by Cushing in a patient with a rare primary pituitary adenoma that secreted ACTH. This condition is known as Cushing s disease. 

ACTH-dependent Cushing s syndrome is usually caused by overproduction of ACTH by the pituitary gland, causing adrenal hyperplasia (Cushing s disease). Pituitary adenomas account for about 80% of these cases. Ectopic ACTH-secreting tumors and nonneoplastic corticotropin hypersecretion are responsible for the remaining 20% of cases. 

Cushing s disease (caused by a pituitary ACTH-secreting adenoma) or Cushing s syndrome from an adrenal tumour is normally treated by surgical removal of the primary lesion where possible. Cases of ectopic ACTH syndrome associated with carcinoma of the bronchus cannot be treated surgically, and often benefit from medical therapy to control adrenal steroid excess. 

Corticotrophin releasing hormone (CRH), corti-coliberin, is a hypothalamic polypeptide that has diagnostic use. It increases ACTH secretion in Cushing s disease secondary to pituitary ACTH-secreting adenoma. It has no therapeutic use. 

Primary adrenal adenoma (Cushing s syndrome) Pituitary adenoma secreting ACTH (Cushing s disease) Exogenous cortisol therapy Excessive licorice ingestion Bartter s syndrome (defective renal CL reabsorption)... 

Interpretation Patients with Cushing s syndrome caused by an ACTH-secreting pituitary adenoma usually show (1) suppression of urinary free cortisol and 17-hydroxycorticosteroid excretion >50% of baseline by day 4 ... 

Somatostatin has been found to inhibit the secretion of various other hormones such as thyrotropin, gastrin inhibitory peptide (GIP), vasoactive intestinal peptide (VIP), pancreozymin, secretin, motilin, gastrin, renin, ACTH in patients with ACTH-secreting pituitary adenoma and ACTH-secretion vitro and to effect exocrine pancreatic function and various GI functions. "21 The physiological significance of these findings is not clear at the present time. 

Cushing disease A specific form of Cushing syndrome, which is caused by an ACTH-secreting pituitary adenoma represents approximately 66 percent of all cases of Cushing syndrome. Because of structural similarities with melanocyte-stimulating hormone (MSH), excess ACTH from pituitary adenomas can induce dermal hyperpigmentation. 

Cushing s disease where a pituitary adenoma secretes ACTH... 

The hypothalamic factors which control anterior pituitary hormone secretion are shown in Figure I. Tumours secreting each of the anterior pituitary hormones have been identified. T.SH and gonadotrophin secreting tumours are rare. Gil and ACTH secreting tumours arc more common. Prolactin secreting adenomas (prolactinomas) arc the most common. 

D. M. Desiderio, J. J. Kusmierz, X. Zhu, C. Dass, D. H. Hilton, J. T. Robertson, and H. S. Sacks, Mass spectrometric analysis of opioid and tachykinin neuropeptides in non-secreting and ACTH-secreting human pituitary adenomas, Biol. Mass Spectrom. 22, 89-97 (1993). 

This is a condition which results from a pituitary adenoma, occuring after total adrenalectomy for Cushing s disease, due to bilateral adrenal hyperplasia. ACTH and MSH may be secreted in response to increased secretion of CRF by the hypothalamus and this results in skin pigmentation. The increased secretion of CRF may be an attempt to maintain the high levels of cortisol that existed before the operation. 

Retinoic acid can also play a potential role in Cushing disease. This malady, i.e. cortisol excess due to an Adre-cocorticotropic Hormone (ACTH)-secreting pituitary adenoma, is a rare disorder with considerable morbidity and mortality but not satisfactory medical treatment as yet. Experimental data have recently shown that retinoic acid restrains Adrecocorticotropic Hormone (ACTH) secrehon by tumoural corticotropes. The aim of the present study was to evaluate the efficacy and safety profile of retinoic acid treatment in pahents with Cushing disease [74 ]. 

Corticotropin secretion is unaff ed by GH-RIH in normal subjects (H3) both basally and in response to insulin hypoglycemia. However, Tyrrell et al. (Tl) have shown a significant faJl in elevated ACTH levels in Nelsons syndrome (4 patients) and in Cushing s disease (1 patient) in response to GH-RIH infusions. These results suggest that the mechanism determining release of ACTH by adenoma cells differ from that in normal pituitary cells. 

The low dose dexamethasone suppression test (qv) is an example of such a test. Dexamethasone is a powerful cortisol analogue which is capable of suppressing ACTH production and therefore cortisol secretion. In Cushing s syndrome, however, the cortisol levels do not fall, e.g. due to pituitary disease (when the feedback mechanism is insensitive) or due to adrenal carcinoma or adenoma when cortisol secretion is auto-nonomous. 

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