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Cushing syndrome

Dr Yuranga Weerakkody and Dr Frank Gaillard et al.

Cushing syndrome is due to the effects of excessive glucocorticoids which may be exogenous or endogenous. In modern western populations, iatrogenic steroid administration for treatment of inflammatory condition is the most common cause, e.g. asthma, rheumatoid arthritis. Endogenous sources of excess cortisol production include:

adrenal adenoma : 20%
primary pigmented nodular adrenal dysplasia (PPNAD) : rare ²
ACTH secreting tumour : 80%
- pituitary adenoma: 85% (Cushing disease)
- ectopic production : 15% (e.g. small cell lung cancer)
adrenocorticotropin (ACTH)-independent macronodular adrenocortical hyperplasia (AIMAH) : is a rare cause of ACTH independent Cushing syndrome ⁴

The work up of Cushing syndrome requires measurement both of cortisol as well as ACTH. Measuring cortisol typically needs to be over a 24 hour period because release is intermittent.

Radiographic features

Imaging of the suspected region is then required (CT or MRI for adrenal glands, MRI (or CT) for pituitary gland). If ACTH is elevated but no microadenoma can be identified, and no ecopic source can be found, then inferior petrosal sinus sampling can be undertaken. Bilateral adrenal hyperplasia is one of the commonest findings on abdominal CT.

ACTH secreting pituitary microadenomas may be inapparent on imaging in 40 to 50% of cases.

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