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How is Cushing’s Syndrome Diagnosed?

Diagnosis of Cushing Syndrome

In women, it presents with many of the symptoms that are synonymous with Polycystic Ovary Syndrome (PCOS). They are susceptible to developing insulin resistance and becoming obese, both of which are risks for those with Cushing’s syndrome.

Cortisol can be measured in the urine, blood and saliva. People with Cushing’s syndrome do not experience this decline in levels. Some people with suspected Cushing’s syndrome will be given a low dose of dexamethasone, which is a glucocorticoid. Doctors will then measure cortisol levels in the blood, with the expectation that low dose steroids should cause a lowering of endogenous cortisol levels.

Endogenous Cushing’s syndrome can be more challenging to accurately diagnose. Blood tests will be utilised to identify whether your syndrome is ACTH-dependent or independent. If measured levels of ACTH are low, the most likely cause is an adrenal tumour (ACTH-independent); higher levels suggest a pituitary (or ACTH-secreting ectopic) tumour. 

Sometimes scans (MRI and/or CT) are performed in an attempt to visualise and localise any tumours. An alternative approach is to take a sample of blood from the petrosal sinuses, which are the veins that are responsible for draining the pituitary gland. At the same time a blood sample will be taken from elsewhere in the body. If levels of ACTH are higher in the sample taken from the petrosal sinus than the other sample, a pituitary tumour is more likely; if levels are consistent across the two samples an ectopic tumour is the more likely cause.

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