Cushing’s Syndrome Caused By Ectopic ACTH Production

There is significant neuromodulation of Cushing's syndrome with only a few patients diagnosed with ectopic production of ACTH with the clinical features of hypercortisolemia. 

Patients may present with centripetal obesity and weight loss for all causes except ectopic ACTH secretion.

Hypokalaemia, metabolic alkalosis, glucose intolerance, fluid retention, hypertension and occasionally steroid psychosis.

It seems that patients suffering from ectopic ACTH syndrome still undergo some weight gain and have redistribution of-fat towards the abdomen but only to a limited extent due to the low duration of exposure to excessive steroids and the cachexia which lessens the possibility for weight and fat accumulation.

The finding of suppressed ACTH levels denies this diagnosis and it points towards an ACTH-independent cause of Cushing's such as prima facie evidence of adrenal or exogenous glucocorticoid suppression.

About 80% of adenomas producing pituitary ACTH have been shown to suppress 8:00 A. M. serum cortisol after administration of dexamethasone(8 mg PO) according to pharmacist orders whilst about 90% of cases producing ectopic ACTH have been unsuccessful in the same effort. 

Ectopic Antidiuretic Secretion 

Before SIADH can be diagnosed , the following criteria must be met:

The cause for which ADH is released should be absent leading to urination of concentrated fluid.

The kidneys as well as adrenal glands should be functioning normally.

Absence of edema or hypovolaemia.

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