Endocrinology - Cushing's Flashcards
Presentation of Cushing’s
Central obesity Round face Abdominal striae Fat pad on upper back (buffalo hump) Proximal limb muscle wasting
High levels of stress hormone causing:
- Hypertension
- Hyperglycaemia (T2DM)
- Depression
- Insomnia
Also:
- Osteoporosis,
- Easy bruising
- Poor wound healing
- Hirsutism
Irregular periods in females
Causes of Cushing’s syndrome
Exogenous steroid treatment
Cushing’s disease (pituitary adenoma releasing excessive ACTH)
Adrenal adenoma
Paraneoplastic Cushing’s
What is paraneoplastic Cushing’s?
Excess ACTH release from a cancer (which then stimulates excess cortisol release) - most commonly from small cell lung cancer, also carcinoid
Diagnostic test for Cushing’s syndrome
Low dose dexamethasone suppression test first
- If abnormal (cortisol not suppressed) - perform high dose dexamethasone suppression test
(24h Urinary free cortisol can be performed as an alternative to Dexa suppression)
How is dexamethasone test done?
Dexamethasone given and then cortisol measured after 48h of dexamethasone
Low dose dexamethasone test:
- Normal - cortisol levels suppressed
- Abnormal - cortisol levels not suppressed = Cushing’s syndrome
- If abnormal, perform high-dose dexamethasone test
High dose dexamethasone test result meanings
8mg dexamethasone used
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.
High dose dexamethasone suppression test shows suppressed cortisol and ACTH…
Cushing’s disease (Pituitary adenoma)
High dose dexamethasone suppression test shows not suppressed cortisol but ACTH is suppressed
Adrenal adenoma
High dose dexamethasone suppression test shows neither cortisol or ACTH are suppressed
Ectopic ACTH secretion e.g. small cell lung cancer
Other investigations in suspected Cushing’s syndrome
BP
FBC - raised white cells) and electrolytes (potassium may be low if aldosterone is also secreted by an adrenal adenoma)
MRI brain (for pituitary adenoma)
CT Thorax (small cell lung cancer)
Abdominal CT (adrenal tumours)
Treatment of Cushing’s syndrome
To surgically remove the underlying tumour cause
Trans-sphenoidal (through the nose) removal of pituitary adenoma
Surgical removal of adrenal tumour
Surgical removal of tumour producing ectopic ACTH
If surgical removal is not possible…
If surgical removal of the cause is not possible another option is to remove both adrenal glands and give the patient replacement steroid hormones for life.