QuestionSBA
QuestionChoice
Although dexamethasone suppression tests are used first line to diagnose Cushing's, low dose (overnight) tests are used not high dose. Morning and midnight ACTH measurements are the gold standards for Cushing's localisation, but a high dose dexamethasone tests can also be used to localise Cushing's pathology:

* Cortisol and ACTH suppressed: Pituitary pathology (Cushing's disease)
* Cortisol not suppressed, ACTH suppressed: adrenal pathology
* Neither cortisol nor ACTH suppressed: ectopic ACTH secretion (e.g. small cell lung cancer)
10000439
d
High-dose dexamethasone suppression test
QuestionChoice
The aldosterone/renin ratio is the first line test for primary hyperaldosteronism, a condition characterised by excess production of the mineralocorticoid aldosterone by the adrenal gland. In individuals with hyperaldosteronism, the aldosterone/renin ratio is increased, due to elevated aldosterone production and the subsequent suppression of renin caused by sodium retention negatively feeding back.
10000437
b
Aldosterone/renin ratio
QuestionChoice
Although a pituitary MRI may be used to identify the presence of a pituitary adenoma (Cushing's disease), it is not the first-line test to diagnose Cushing's syndrome. Instead, a low-dose dexamethasone suppression test should be used to establish the presence of excess cortisol production.
10000440
e
Pituitary MRI
QuestionChoice
This patient is most likely suffering from Cushing's syndrome, a disease characterised by excess circulating cortisol which may have a range of causes including exogenous corticosteroid exposure or pituitary adenoma. Cushing's syndrome presents with features of glucocorticoid excess: hypertension, insulin insensitivity, central obesity, proximal muscle weakness, striae, moon facies, and menstrual irregularities. The low-dose dexamethasone suppression test is first line and assesses the body's response to exogenous glucocorticoid. In health, the body will suppress the morning cortisol spike due to the negative feedback effect. In individuals with Cushing's syndrome, the morning cortisol increase will still be present.
10000436
a
Low-dose dexamethasone suppression test
QuestionChoice
The ACTH stimulation test (also known as the short synacthen test) is the definitive investigation of Addison's disease, not Cushing's syndrome. Addison's disease is characterised by primary adrenal insufficiency, so the provision of exogenous ACTH does not stimulate cortisol production. ACTH measurement also plays a role in Cushing's syndrome diagnosis, but is not the first line investigation and is instead used to localise the pathology involved.
10000438
c
ACTH stimulation test
Concept
Chapter
2693
3764
Cushing's syndrome
Topic
133
Endocrinology
12634
A 43-year-old male presents to the clinic with a 2-month history of central weight gain and difficulty rising from chairs.

On examination, you note central obesity and proximal muscle weakness.

Furthermore, you identify a blood pressure of 146/93 mmHg and a heart rate of 81 bpm. Which of the following investigations is first line for the most likely underlying condition?
a