Thyroid

Question 1

What are the thyroid hormones?

Answer 1

T3 (Triiodothyronine) as active hormone
Derived from T4 (Tertaiodothyronine)
Extensively protein bound in plasma

Question 2

What are the thyroid states?

Answer 2

Euthyroid state – Thyroid hormone secretion is normal
Hypothyroid state - Thyroid hormone secretion is subnormal (myxoedema)
Hyperthyroid state - Thyroid hormone secretion is excessive (thyrotoxicosis)

Question 3

What are the actions of thyroid stimulating hormone (TSH)?

Answer 3

TSH increases protein synthesis in follicular epithelial cells, DNA replication, and cell division
Increases rough endoplasmic reticulum and cell machinery required for protein synthesis
Thyroid will undergo hypertrophy if exposed to greater TSH concentration
Results in goitre

Question 4

Thyroid functioning test normal results ?

Answer 4

TSH- 0.27-4.2 mU/L
Free T4- 12-22 pmol/L
Free T3- 3.1-6.8 pmol/L

Question 5

Symptoms of hypothyroidism?

Answer 5

Cold intolerance, Weight gain, Bradycardia, Tiredness for no apparent reason, Constipation, Forgetfulness and personality changes, Pale or dry coarse skin, Puffiness of face

Question 6

What is primary hypothyroidism?

Answer 6

Any condition characterised by plasma T3 or T4 below normal and increased TSH
Due to damage or loss of thyroid tissue

Question 7

What are the causes of primary hypothyroidism?

Answer 7

Hashimoto’s thyroiditis- ost common cause
Autoimmune disease (antibodies to thyroid peroxidase)
Twice as prevalent in women
T4 decreases and TSH increases
Can result in goitre

Question 8

Treatment of hypothyroidism?

Answer 8

Levothyroxine or Liothyronine

Question 9

Levothyroxine?

Answer 9

Synthetic thyroid hormone that is identical to thyroxine (T4)
Dose adjusted until TSH levels are in mid-range
Yearly monitoring
Pregnant women require 50-100% more dose

Question 10

Side effects of levothyroxine?

Answer 10

Hair loss during the first few months of treatment
Headaches
Sleep problems (insomnia)
Nervousness
Fever, hot flashes and/or sweating
Pounding heart beat or fluttering in chest
Appetite changes, weight changes

Question 11

Liothyronine?

Answer 11

Synthetic form of T3
Controversy surrounds its use in the treatment of hypothyroidism
(Not supported in The Royal College of Physicians Consensus Statement on “The Diagnosis and Management of Primary Hypothyroidism”)
Risks from T3 therapy on bone (osteoporosis) and heart (arrhythmia)

Question 12

What is secondary hypothyrodism?

Answer 12

Uncommon
Pituitary doesn’t produce TSH or hypothalamus doesn’t produce sufficient TRH (tertiary)
Both T3 and T4, as well as TSH are below normal
Symptoms very similar to primary hypothyroidism and treated in same manner

Question 13

What is myxoedema coma?

Answer 13

End result of untreated hypothyroidism
Progressive weakness leading to a loss of consciousness, Extreme hypothermia (24-32oC), Areflexia, seizures, and respiratory depression
Medical emergency requiring urgent treatment

Question 14

What are the symptoms of hyperthyroidism?

Answer 14

Heat intolerance, Palpitations, Weight loss, Restlessness and nervousness, Fatigue, Increased sweating, Frequent bowel movements
Goitre may be present

Question 15

What is hyperthyroidism?

Answer 15

Thyroid produces an excess of T4
Reduction in TSH due to negative feedback loop
T3 is usually elevated as well

Question 16

What is Graves Disease?

Answer 16

Most common cause of hyperthyroidism
Goiter, protruding eyebalss
Autoimmune disease
Caused by thyroid stimulating immunogloblin (TSI)
Activates TSH receptor on thyroid follicular cells
Increased secretion of thyroid hormones

Question 17

Anti-thyroid drugs?

Answer 17

Thioamides (e.g. carbimazole, propylthiouracil)
Accumulated by the thyroid
Inhibit thyroid peroxidase and prevent hormone synthesis
Propylthiouracil also inhibits peripheral deiodination
Effect is slow in onset (4-6 weeks)
Generally safe but may cause agranulocytosis, thereby increasing the risk of infection