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CUSHING SYNDROME-INVESTIGATIONS

Endocrinology

CUSHING SYNDROME-INVESTIGATIONS

1. Initial tests are to establish the presence of cortisol excess:
- 24-hour urine free cortisol (UFC). In the plasma, < 5% of cortisol is free and physiologically active. Only the free cortisol is filtered by the glomerulus, so urinary cortisol is always "free" cortisol and reflects plasma free cortisol levels
- Late-night salivary cortisol
- Low-dose dexamethasone suppression test to confirm excess cortisol

2. Is the Cushing syndrome ACTH-dependent or ACTH-independent?
- Check the ACTH level. Normally, a high cortisol completely suppresses ACTH production.

3. If ACTH-dependent Cushing syndrome: order neuro-imaging, chest & abdominal imaging.

4. If ACTH-independent Cushing syndrome: high cortisol and low ACTH-most likely an adrenal tumor (adenoma or carcinoma) that is secreting cortisol. Image the adrenals with contrasted CT.


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REFERENCES

1. Wilkinson, I. (2017). Oxford handbook of clinical medicine. Oxford: Oxford University Press.
2. Hannaman, R. A., Bullock, L., Hatchell, C. A., & Yoffe, M. (2016). Internal medicine review core curriculum, 2017-2018. CO Springs, CO: MedStudy.
3. Image:

1. Initial tests are to establish the presence of cortisol excess:
- 24-hour urine free cortisol (UFC). In the plasma, < 5% of cortisol is free and physiologically active. Only the free cortisol is filtered by the glomerulus, so urinary cortisol is always "free" cortisol and reflects plasma free cortisol levels
- Late-night salivary cortisol
- Low-dose dexamethasone suppression test to confirm excess cortisol

2. Is the Cushing syndrome ACTH-dependent or ACTH-independent?
- Check the ACTH level. Normally, a high cortisol completely suppresses ACTH production.

3. If ACTH-dependent Cushing syndrome: order neuro-imaging, chest & abdominal imaging.

4. If ACTH-independent Cushing syndrome: high cortisol and low ACTH-most likely an adrenal tumor (adenoma or carcinoma) that is secreting cortisol. Image the adrenals with contrasted CT.

Ⓒ A. Manickam 2018

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