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%
- 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.
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.
- 1. Miller DL, Doppman JL. Petrosal sinus sampling: technique and rationale. Radiology. 1991;178 (1): 37-47. Radiology (abstract) - Pubmed citation
- 2. Rockall AG, Babar SA, Sohaib SA et-al. CT and MR imaging of the adrenal glands in ACTH-independent cushing syndrome. Radiographics. 24 (2): 435-52. doi:10.1148/rg.242035092 - Pubmed citation
- 3. Swearingen B. Cushing's Disease. Springer Verlag. (2011) ISBN:1461400104. Read it at Google Books - Find it at Amazon
- 4. Doppman JL, Chrousos GP, Papanicolaou DA et-al. Adrenocorticotropin-independent macronodular adrenal hyperplasia: an uncommon cause of primary adrenal hypercortisolism. Radiology. 2000;216 (3): 797-802. Radiology (full text) - Pubmed citation
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