Cushing's Syndrome Flashcards
What is Cushing’s syndrome?
Cushing’s Syndrome is used to refer to the signs and symptoms that develop after prolonged abnormal elevation of cortisol.
What is Cushing’s disease?
Cushing’s Disease is used to refer to the specific condition where a pituitary adenoma (tumour) secretes excessive ACTH.
Cushing’s disease causes cushing’s syndrome, T/F?
Cushing’s Disease causes a Cushing’s syndrome, but Cushing’s Syndrome is not always caused by Cushing’s Disease.
What are the features of cushing’s syndrome?
Round in the middle with thin limbs:
Round “moon” face Central Obesity Abdominal striae Buffalo Hump (fat pad on upper back) Proximal limb muscle wasting High levels of stress hormone:
Hypertension Cardiac hypertrophy Hyperglycaemia (Type 2 Diabetes) Depression Insomnia Extra effects:
Osteoporosis
Easy bruising and poor skin healing
What are the causes of cushing’s syndrome?
- Exogenous steroids (in patients on long term high dose steroid medications)
- Cushing’s Disease (a pituitary adenoma releasing excessive ACTH)
- Adrenal Adenoma (a hormone secreting adrenal tumour)
- Paraneoplastic Cushing’s
What is paraneoplastic cushing’s?
Paraneoplastic Cushing’s is when excess ACTH is released from a cancer (not of the pituitary) and stimulates excessive cortisol release. ACTH from somewhere other than the pituitary is called “ectopic ACTH”. Small Cell Lung Cancer is the most common cause of paraneoplastic Cushing’s.
What investigation is used to diagnose cushing’s syndrome?
The dexamethasone suppression test
What is the dexamethasone suppression test?
The dexamethasone suppression test is the test of choice for diagnosing Cushing’s Syndrome. This involves initially giving the patient the “low dose” test. If the low dose test is normal, Cushing’s can be excluded. If the low dose test is abnormal, then a high dose test is performed to differentiate between the underlying causes.
How is the dexamethasone test performed?
To perform the test the patient takes a dose of dexamethasone (a synthetic glucocorticoid steroid) at night (i.e. 10pm) and their cortisol and ACTH is measured in the morning (i.e. 9am). The intention is the find out whether the dexamethasone suppresses their normal morning spike of cortisol.
Explain the results of a low dose dexamethasone suppression test (1mg dexamethasone)?
A normal response is for the dexamethasone to suppress the release of cortisol by effecting negative feedback on the hypothalamus and pituitary. The hypothalamus responds by reducing the CRH output. The pituitary response by reducing the ACTH output. The lower CRH and ACTH levels result in a low cortisol level. When the cortisol level is not suppressed, this is the abnormal result seen in Cushing’s Syndrome.
Explain the results of a high dose dexamethasone suppression test (8mg dexamethasone)?
The high dose dexamethasone suppression test is performed after an abnormal result on the low dose test.
In Cushing’s Disease (pituitary adenoma) the pituitary still shows some response to negative feedback and 8mg of dexamethasone is enough to suppress cortisol.
Where there is an adrenal adenoma, cortisol production is independent from the pituitary. Therefore, cortisone is not suppressed however ACTH is suppressed due to negative feedback on the hypothalamus and pituitary gland.
Where there is ectopic ACTH (e.g. from a small cell lung cancer), neither cortisol or ACTH will be suppressed because the ACTH production is independent of the hypothalamus or pituitary gland.
In a high dose suppression test, what do the results show if its is a pituitary adenoma?
Cortisol = suppressed ACTH = Suppressed
In a high dose suppression test, what do the results show if its is an adrenal adenoma?
Cortisol = not suppressed ACTH = suppressed
In a high dose suppression test, what do the results show if its is ectopic ACTH?
Cortisol = not suppressed ACTH = Not suppressed
What other investigations could you do to assess for Cushing’s syndrome?
24hr urinary free cortisol.
- FBC - (raised WCC) and electrolytes (potassium may be low if aldosterone is also secreted by an adrenal adenoma).
- MRI brain for pituitary adenoma
- Chest CT for small cell lung cancer
- Abdominal CT for adrenal tumours.
