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Chapter: Medicine Study Notes : Endocrine and Electrolytes

Cushing’s Syndrome

Chronic glucocorticoid excess, either exogenous or endogenous (adrenal or pituitary neoplasm, or ectopic ACTH secretion)

Cushing’s Syndrome

 

·        = Chronic glucocorticoid excess, either exogenous or endogenous (adrenal or pituitary neoplasm, or ectopic ACTH secretion)

 

·        Signs: Tissue wasting, myopathy, thin skin, purple abdominal striae, easy bruising, osteoporosis, water retention, supraclavicular fat-pad (“buffalo hump”), predisposition to infection, bad wound healing, hirsutism, amenorrhoea, hyperglycaemia (30%)

 

·        Tests:

 

o   Confirm source biochemically before looking radiologically. CT adrenal „incidentalomas‟ are common Þ does not prove adrenal source of cortisol excess

o   Screening tests:

 

§  24h urinary free cortisol (normal < 280 nmol/24 hr). If positive then high dose dexamethasone suppression test.

 

§  Alternative is low dose dexamethasone suppression test: give 1 mg po at midnight, check cortisol at 8 am (normal 450 – 700 nmol/L). False positives with depression, obesity and drugs affecting metabolism of dexamethasone (eg phenytoin, phenobarbitone)

 

§  Midnight cortisol nearly as good: but must do as an inpatient (need to wake to do it and be unstressed) – midnight is low point of diurnal cycle, if high then diurnal cycle depressed

o   Do high dose dexamethasone test (8mg) to determine type of Cushing‟s or if obese


·        Causes and treatment:

 

o   Exogenous corticosteroid administration: reduce as much as possible. In asthma, use inhaled steroids


o   Cushing‟s Disease: (adrenal hyperplasia secondary to pituitary tumour, F > M, peak age 30 – 50).

 

o   Some, but not normal, suppression of cortisol with high dose dexamethasone. Treatment: Surgical removal of pituitary adenoma

 

o   Adrenal gland adenoma or carcinoma: No suppression of cortisol with high dose.  Undetectable

 

o   ACTH. Treatment: surgical removal

 

·        Ectopic ACTH production: especially small cell carcinoma of the lung and carcinoid. No suppression of cortisol with high dose dexamethasone. Plasma ACTH generally >250 ng/L. Hypokalaemic alkalosis is common. CT relevant areas (lung, pancreas, mediastinum, thyroid)

 

·        Can block adrenal cortisol production with ketoconazole

 

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Medicine Study Notes : Endocrine and Electrolytes : Cushing’s Syndrome |


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