Normal Thyroid Physiology & Regulation
What hormone from the pituitary gland stimulates the thyroid gland?
TSH (thyroid-stimulating hormone)
What is the most common cause of hyperthyroidism?
Answer: Graves disease.
What is the most common cause of hypothyroidism in iodine-sufficient countries?
Answer: Hashimoto thyroiditis.
What is a goitre?
Enlargement of the thyroid gland
What cardiac arrhythmia is commonly associated with hyperthyroidism?
Atrial fibrillation
Which two thyroid hormones are produced by the thyroid gland?
Answer: T3 (triiodothyronine) and T4 (thyroxine).
What autoantibody is responsible for Graves disease?
Answer: TSH receptor antibodies (TRAb), also called thyroid-stimulating immunoglobulins (TSI).
Which antibodies are commonly found in Hashimoto thyroiditis?
Answer:
Why does iodine deficiency cause enlargement of the thyroid gland?
Low iodine → low T3/T4 → increased TSH → thyroid hypertrophy and hyperplasia
What is the term used for severe, life-threatening hyperthyroidism?
Thyroid storm
Which thyroid hormone is produced in greater quantities by the thyroid gland: T3 or T4?
Answer: T4 is produced in much larger quantities.
Is Graves disease usually associated with hyperthyroidism or hypothyroidism?
Answer: Hyperthyroidism.
Is Hashimoto thyroiditis usually associated with hyperthyroidism or hypothyroidism?
Answer: Hypothyroidism.
Is de Quervain (subacute granulomatous) thyroiditis usually painful or painless?
How does excess thyroid hormone increase the risk of atrial fibrillation?
Thyroid hormone increases β1-receptor expression and cardiac excitability, promoting ectopic activity and AF.
Explain why low iodine intake leads to elevated TSH levels.
Answer: Iodine is required to make T3 and T4. If iodine intake falls, the thyroid cannot produce enough thyroid hormone. Reduced T3/T4 means less negative feedback on the hypothalamus and pituitary, causing increased TSH release. The elevated TSH attempts to stimulate the thyroid to produce more hormone.
In Graves disease, is radioactive iodine uptake increased or decreased?
Answer: Increased.
Compare the underlying autoimmune mechanisms of Graves disease and Hashimoto thyroiditis.
Graves Disease vs Hashimoto Thyroiditis
Autoantibodies stimulate TSH receptor vs Immune cells destroy thyroid tissue
Increased hormone production vs Reduced hormone production
Hyperthyroidism vs Hypothyroidism
Thyroid gland is overactive vs Thyroid gland is progressively destroyed
A useful memory trick:
Why can a patient with thyroiditis initially present with symptoms of hyperthyroidism?
Inflammation damages follicles, releasing preformed thyroid hormone into circulation.
A patient has elevated T4, suppressed TSH, and low radioactive iodine uptake. Which thyroid condition would this pattern most strongly suggest?
Thyroiditis, because hormone is leaking from damaged follicles rather than being newly synthesised.
Why does Graves disease often cause a diffuse goitre?
Answer:
A patient has weight loss, heat intolerance, tremor, diffuse goitre, and increased radioactive iodine uptake. What is the most likely diagnosis and why?
Answer: Graves disease.
Reasoning:
Why can Graves ophthalmopathy and pretibial myxoedema persist even after thyroidectomy?
Explain the pathophysiological sequence from chronic iodine deficiency to multinodular goitre.
Chronic iodine deficiency → reduced T3/T4 → increased TSH → diffuse thyroid enlargement → repeated cycles of growth and involution → nodular transformation → multinodular goitre.
Explain the mechanism by which thyroid storm can lead to severe tachycardia, atrial fibrillation, heart failure, and death.
Excess thyroid hormone dramatically increases sympathetic sensitivity, heart rate, myocardial oxygen demand, and atrial automaticity, leading to AF, high-output heart failure, shock, and multiorgan dysfunction.