Investigating the Endocrine System

Question 1

Types of hormone

Answer 1

Peptide (e.g PTH, ACTH, TSH)
Steroid (e.g. Testosterone, Oestradiol, Cortisol)
Tyrosine-based (e.g. T3, T4)

Question 2

TBG

Answer 2

Carries thyroid hormone but only unbound forms are physiologically active
If level of TBG changes, this results in a change in the level of the free hormones
Therefore measurement of total hormone levels can be misleading

Question 3

Causes of increased TBG

Answer 3

Genetics
Pregnancy
Oestrogens

Question 4

Causes of decreased TBG

Answer 4

Genetics
Protein-losing status
Malnutrition
Malabsorption
Acromegaly
Cushing's
High dose corticosteroids
Severe illness
Androgens

Question 5

Low TSH, low thyroxine

Answer 5

Pituitary failure

Question 6

Low TSH, high thyroxine

Answer 6

Thyroid gland overproduction (e.g. Graves’)

Question 7

High TSH, low thyroxine

Answer 7

Unresponsive thyroid

Question 8

High TSH, high thyroxine

Answer 8

Pituitary gland overproduction or feedback fails (rare)

Question 9

“Sick euthyroid disease”

Answer 9

No point in measuring thyroid hormones in critically unwell patients - will be all over the place and difficult to interpret

Question 10

Repetition of TFTs (guidelines)

Answer 10

Repeat every 3 years in healthy patients (unlikely)
Graves’ - 1-2 months after radioactive iodine, then 4-6 week intervals if remain thyrotoxic, or 6-8 weeks following thyroidectomy
Hypothyroidism - 2 months, but not before this due to lag period of thyroxine, if stabilised, then annually

Question 11

Immunoassays

Answer 11

Use of monoclonal antibodies
Alternative labelling for H&S reasons
Widely used due to antibody specificity, sensitivity and that it is amenable to automation

Question 12

Interference in immunoassay

Answer 12

Cross-linking antibody causing positive interference
Blocking antibody causing negative intereference
Usually a different test done if the test results do not match the patient

Question 13

Clinical features of phaeochromocytomas

Answer 13

Excessive and episodic release of catecholamines may results in paroxysmal features:
Hypertension
Sweating, pallow
Panic attacks
Headaches
Abdo pain
Can also be asymptomatic

Question 14

Testing for phaeochromocytomas

Answer 14

Using epinephrines due to the fact that it is more stable in the blood than catecholamines

Question 15

Whipple’s Triad

Answer 15

Signs and symptoms of hypoglycaemia
Low plasma glucose
Resolution of symptoms once glucose level rises

Question 16

Symptoms of hypoglycaemia

Answer 16

Hunger, sweating, anxiety parenthesis, palpitations, tremulousness, weakness, fatigue, dizziness, headache, confusion, behavioural changes, cognitive dysfunction, blurred vision, diplopia

Question 17

Signs of hypoglycaemia

Answer 17

Pallor, tachycardia, widened pulse pressure, cortical blindness, hypothermia, seizures, coma

Question 18

Common endogenous causes of hypoglycaemia

Answer 18

Insulinomas
Insulin antibodies
Critical organ failure
Sepsis
Hormone deficiency

Question 19

Common exogenous causes of hypoglycaemia

Answer 19

Overuse of insulin
Drug interactions
Alcohol or other toxins

Question 20

Insulinoma

Answer 20

Most common tumours from islets of Langerhans
Highest incidence 40-60 years
More females than males

Question 21

Diagnosis of insulinoma

Answer 21

Fasting blood test
Low blood sugar (less than 2.2 mol/l)
High insulin (6 microunits/ml or higher)
High levels of C peptide (0.2 mol/l or higher)

Question 22

Features of Cushing’s syndrome

Answer 22

Obesity - moon face, central obesity, shoulders
Skin - thin, purple striae, bruising
Hypertension
Glucose intolerance
Menstural disturbances/impotence
Thin limbs/muscle weakness
Back pain from osteoporosis
Psychiatric disturbances - depression, psychoses

Question 23

Difference between Cushing’s syndrome and disease

Answer 23

Cushing’s syndrome is any high cortisol condition

Cushing’s disease is specifically pituitary ACTH secreting tumour

Question 24

Causes of Cushing’s syndrome

Answer 24

Pituitary ACTH secreting tumour (Cushing’s disease)
Cortisol producing tumour in the adrenal gland
Ectopic ACTH producing tumour
Iatrogenic

Question 25

Dexamethasone test

Answer 25

Test for Cushing’s
High cortisol should be decreased in an overnight suppression test with dexmethasone 1mg
If cortisol does not decrease - Cushing’s can be diagnosed