Thyroid Flashcards
What are the two main hormones produced by the thyroid gland?
Thyroxine (T4) and Triiodothyronine (T3).
What is the primary function of thyroid hormones?
They regulate cell differentiation, organogenesis, thermogenesis, and metabolic homeostasis.
What is the normal weight range of the thyroid gland?
12–20 grams.
What is the role of TSH in thyroid function?
TSH stimulates thyroid hormone synthesis and secretion.
What is the classic endocrine feedback loop in thyroid regulation?
Hypothalamic TRH stimulates pituitary TSH, which stimulates thyroid hormone production.
What is the first step in laboratory evaluation of thyroid function?
Measure TSH levels to determine if they are suppressed, normal, or elevated.
What does a suppressed TSH level (<0.01 mIU/L) typically indicate?
Thyrotoxicosis.
What is the difference between thyrotoxicosis and hyperthyroidism?
Thyrotoxicosis is the state of thyroid hormone excess, while hyperthyroidism is caused by excessive thyroid hormone production by the thyroid gland.
What are the major causes of thyrotoxicosis?
Graves’ disease, toxic multinodular goiter (MNG), and toxic adenomas.
What percentage of thyrotoxicosis cases are caused by Graves’ disease?
60–80%.
What is the most common age range for Graves’ disease onset?
Between 20 and 50 years of age.
What are the environmental factors associated with Graves’ disease?
Stress, smoking, sudden increases in iodine intake, and certain drugs (e.g., HAART, alemtuzumab).
What is the hallmark of Graves’ ophthalmopathy?
Infiltration of extraocular muscles by activated T cells, leading to proptosis and diplopia.
What is the most common cardiovascular manifestation of thyrotoxicosis?
Sinus tachycardia.
What is apathetic thyrotoxicosis?
A form of thyrotoxicosis in the elderly characterized by fatigue and weight loss, often mistaken for depression.
What is the treatment of choice for Graves’ hyperthyroidism?
Antithyroid drugs (e.g., methimazole, propylthiouracil), radioiodine therapy, or thyroidectomy.
What is the starting dose of methimazole for hyperthyroidism?
10–20 mg every 8 or 12 hours.
What is the role of beta-blockers in thyrotoxicosis?
They control adrenergic symptoms such as tachycardia and palpitations.
What is the main complication of radioiodine therapy?
Hypothyroidism due to destruction of thyroid cells.
What is thyroid storm?
A life-threatening exacerbation of hyperthyroidism characterized by fever, delirium, and cardiovascular collapse.
What is the mortality rate of thyroid storm?
Up to 30% even with treatment.
What is the first-line treatment for thyroid storm?
Large doses of PTU (500–1000 mg loading dose) followed by stable iodide and beta-blockers.
What is the most common cause of hypothyroidism worldwide?
Iodine deficiency.
What is the most common cause of hypothyroidism in iodine-sufficient areas?
Autoimmune disease (Hashimoto’s thyroiditis).
What is the hallmark of Hashimoto’s thyroiditis?
Lymphocytic infiltration of the thyroid with germinal center formation and thyroid follicle atrophy.
What is the annual risk of developing clinical hypothyroidism in subclinical hypothyroidism with positive TPO antibodies?
About 4%.
What is the typical dose of levothyroxine for hypothyroidism?
1.6 μg/kg body weight (usually 100–150 μg/day).
What is the goal of levothyroxine therapy in hypothyroidism?
To normalize TSH levels and relieve symptoms.
What is myxedema coma?
A life-threatening complication of severe hypothyroidism characterized by reduced consciousness, hypothermia, and metabolic disturbances.
What is the mortality rate of myxedema coma?
20–40% despite treatment.
What is the initial treatment for myxedema coma?
IV levothyroxine (200–400 μg loading dose) and hydrocortisone (50 mg every 6 hours).
What is the role of thyroid ultrasound in thyroid disease?
It helps diagnose nodular thyroid disease and assess suspicious sonographic features (e.g., hypoechoic nodules with microcalcifications).
What is the most common sonographic feature of malignant thyroid nodules?
Hypoechoic solid nodules with infiltrative borders and microcalcifications.
What is the role of TPO antibodies in autoimmune thyroid disease?
They are present in up to 80% of Graves’ disease and almost all autoimmune hypothyroidism cases.
What is the main role of thyroglobulin (Tg) measurement?
To monitor thyroid cancer patients after thyroidectomy.
What is the typical radionuclide scan finding in Graves’ disease?
Diffuse, high uptake of tracer.
What is the typical radionuclide scan finding in toxic multinodular goiter?
Multiple areas of relatively increased uptake.
What is the most common cause of toxic multinodular goiter?
Functional autonomy of thyroid nodules over time.
What is the most common symptom of toxic multinodular goiter?
Hyperthyroidism with a nodular thyroid on palpation.
What is the treatment for toxic multinodular goiter?
Radioiodine therapy or thyroidectomy.
What is the most common cause of hypokalemic periodic paralysis in thyrotoxicosis?
Excess thyroid hormone leading to intracellular potassium shifts.
What is the most common ocular manifestation of Graves’ disease?
Grittiness, eye discomfort, and excess tearing.
What is thyroid dermopathy?
A noninflamed, indurated plaque with an orange-peel appearance, occurring in <5% of Graves’ disease patients.
What is thyroid acropachy?
A form of clubbing found in <1% of Graves’ disease patients.
What is the role of glucocorticoids in thyroid storm?
They reduce T4-to-T3 conversion and treat potential adrenal insufficiency.
What is the Wolff-Chaikoff effect?
High iodine intake temporarily inhibits thyroid hormone synthesis.
What is the most common cause of hypothyroidism in pregnancy?
Autoimmune thyroiditis (Hashimoto’s thyroiditis).
What is the recommended levothyroxine dose adjustment during pregnancy?
Increase by up to 45% to maintain normal TSH levels.
What is the most common cause of subclinical hypothyroidism?
Autoimmune thyroiditis with mildly elevated TSH and normal T4 levels.
What is the treatment for subclinical hypothyroidism with TSH >10 mIU/L?
Levothyroxine therapy to normalize TSH levels.
