Endocrine

Question 1

Investigations to Diagnose Cushing’s?

Answer 1

Dexamethasone Suppression Test

• First Low Dose (1mg dex) taken at night, cortisol and ACTH measured first thing in morning to see whether dexamethasone suppressed morning cortisol spike. Normal is low Cortisol and ACTH.
• If abnormal then proceed to High Dose Dex Supression Test.

Other Investigations:

• FBC
• U/Es (K+ Low if Aldosterone also secreted by adrenal adenoma)
• MRI Brain (Pituitary Adenoma)
• Chest CT (Small Cell Lung Cancer)
• Abdominal CT (Adrenal Tumor)

Question 2

High Dose Dexamethasone Suppression Test Results:

• Cortisol Suppressed
• ACTH Suppressed

Answer 2

Pituitary Adenoma

Question 3

High Dose Dexamethasone Suppression Test Results:

• Cortisol Not Suppressed
• ACTH Suppressed

Answer 3

Adrenal Adenoma

Question 4

High Dose Dexamethasone Suppression Test Results:

• Cortisol Not Suppressed
• ACTH Not Suppressed

Answer 4

Ectopic ACTH (Small Cell Lung Cancer)

Question 5

Causes of Primary Adrenal Insufficiency?

Answer 5

Addison’s Disease (Most commonly autoimune)

Reduction in cortisol and aldosterone

Question 6

Causes of Secondary Adrenal Insufficiency?

Answer 6

Inadequate ACTH (Damage to pituitary due to surgery, infection, loss of blood flow)

Sheehan’s Syndrome (massive blood loss in childbirth => Pituitary necorsis)

Question 7

Causes of Tertiary Adrenal Insufficiency?

Answer 7

Inadequate CRH release by the hypothalamus (long term steroids => Suppression of hypothalamus => quickly withdrawn not enough time to upregulate endogenous steroids)

Question 8

Symptoms/Signs of Adrenal Insufficiency

Investigations/Diagnosis?

Answer 8

Symptoms: Fatigue, Nausea, Cramps, Reduced Libido

Signs:

• Bronze hyperpigmentation (ACTH stimulated melanocytes to produce melanin)
• Hypotension

Investigations:

• Hyponatremia
• Hyperkalemia
• Synacthen Test is diagnostttic. Synacthen ((Synthetic ACTH) given first thing in morning then blood cortisol is measured at 30 mins and 60 mins following administration. Failure of cortisol to double = Addisons

Question 9

Imaging thyroid investigations

Answer 9

Thyroid ultrasound (Cystic vs. Solid Nodules)

Radioisotope scans investigate hyperthyroidism/thyroid cancer

• Diffuse = Graves
• Focal = Toxic multinodular goitre and adenoma
• Cold = thyroid cancer

Question 10

Dignosing Diabetes?

Answer 10

Random plasma glucose ≥ 11.1mmol/l

Fasting plasma glucose ≥ 7.0mmol/l

Plasma glucose of ≥ 11.1mmol/l two hours post OGTT

HbA1c ≥ 48mmol/mol (≥6.5%)