D&E - Adrenal Axis Flashcards
Describe the adrenal axis.
- Hypothalamus secretes CRH.
- Cortisol stimulates anterior pituitary to release ACTH.
- ACTH stimulates the adrenal glands to release cortisol.
What are the actions of cortisol within the body?
- increased alertness
- inhibits the immune system
- inhibits bone formation
- raised blood glucose
- increases metabolism
What is adrenal insufficiency?
The condition in which the adrenal glands do not produce enough steroid hormones, cortisol and aldosterone.
What is Addison’s disease?
Adrenal insufficiency when the adrenal glands have been damaged, resulting in reduce cortisol and aldosterone secretion.
What are the causes of secondary adrenal insufficiency?
Inadequate ACTH release from the pituitary:
- pituitary adenomas
- surgery to the pituitary
- trauma
What is tertiary adrenal insufficiency?
Inadequate CRH release by the thalamus, usually a result of taking long-term oral steroids.
When exogenous steroids are suddenly withdrawn, the hypothalamus is not able to adequately replace with endogenous steroids.
This is why long-term steroids must be tapered slowly, to allow the adrenal axis to regain normal function.
Presentation of adrenal insufficiency.
- fatigue
- muscle weakness
- muscle cramps
- dizziness and fainting
- thirst and craving salt
- weight loss
- abdominal pain
- depression
- reduced libido
What are the signs of adrenal insufficiency, and why do these occur?
Bronze hyperpigmentation of the skin due to excess ACTH. ACTH stimulates melanocytes to produce melanin.
Hypotension.
What are the biochemical findings in adrenal insufficiency?
- hyponatraemia
- hyperkalaemia
- hypercalcaemia
- hypoglycaemia
- raised creatinine and urea (urea > creatinine = dehydration)
Which autoantibodies are associated with Addison’s disease?
- adrenal cortex antibodies
- 21-hydroxylase antibodies
What is the diagnostic test for pituitary insufficiency?
Short Synacthen test / ACTH stimulation test.
A dose of synthetic ACTH (Synacthen) is given in the morning, with blood cortisol checked before and after (30m, 60m) the dose.
The cortisol level should at least double in a healthy individual.
How is adrenal insufficiency managed?
- hydrocortisone to replace cortisol
- fludrocortisone to replace aldosterone
Patients are given a steroid card, ID tag and emergency letter to alert emergency services that they depend on steroids for life.
How are steroid doses altered during acute illness, for patients with adrenal insufficiency?
Doses are doubled during acute illness, to match the normal steroid response to illness.
What is Addisonian crisis?
An acute presentation of severe adrenal insuffieincy, where the absence of steroid hormones leads to life threatening emergency.
Presentation of Addisonian crisis?
- reduced consciousness
- hypotension
- hypoglycaemia
- hyponatraemia
- hypokalaemia
What are the triggers for Addisonian crisis?
- infection
- trauma
- acute illness
How should Addisonian crisis be managed?
- ABCDE approach to initial assessment
- IM hydrocortisone
- IV fluids
- correct hypoglycaemia (e.g. IV dextrose)
- careful monitoring of electrolytes and fluid balance
Define:
a) Cushing’s syndrome
b) Cushing’s disease
a) prolonged elevated levels of cortisol within the body.
b) prolonged elevated levels of cortisol within the body, secondary to an ACTH-secreting pituitary adenoma, stimulating excess cortisol release from the adrenal glands.
Causes of Cushing’s syndrome.
CAPE
Cushing’s disease (pituitary adenoma ACTH releasing).
Adrenal adenoma (adrenal tumour secreting excess cortisol).
Paraneoplastic syndromes
Exogenous steroids (most common)
Presentation of Cushing’s syndrome.
- anxiety
- depression
- insomnia
- round face
- central obesity
- abdominal striae
- hirsutism
- easy bruising
- hyperpigmentation of skin
What are the metabolic effects of Cushing’s syndrome?
- hypertension
- cardiac hypertrophy
- T2DM
- dyslipidaemia
- osteoporosis
Which paraneoplastic syndromes may cause Cushing’s syndrome?
Small cell lung cancer commonly causes ectopic ACTH release, stimulating excessive cortisol release from the adrenal glands.
How is Cushing’s syndrome diagnosed?
Dexamethasone suppression test to diagnose Cushing’s syndrome caused by a problem inside the body.
What is the normal physiological response to the dexamethasone suppression test?
Dexamethasone induces negative feedback upon the hypothalamus, reducing CRH output.
It also induces negative feedback on the anterior pituitary, reducing ACTH output.
Low CRH and ACTH output causes a low cortisol output by the adrenal glands.
A lack of cortisol suppression in response to dexamethasone suggests Cushing’s syndrome.
