Thyroid

Question 1

define secondary hypothyroidism

Answer 1

inadequate secretion/production of thyroid-stimulating hormone (TSH) from the pituitary gland

Question 2

define tertiary hypothyroidism

Answer 2

inadequate secretion/production of thyrotropin-releasing (TRH) from the hypothalamus

Question 3

most common cause of primary hypothyroidism

Answer 3

Hashimoto’s thyroiditis

Question 4

pathogenesis of Hashimoto’s thyroiditis

Answer 4

autoimmune disorder with antibodies against thyroidal antigens including thyroglobulin, thyroid peroxidase, and TSH receptor –> primary hypothyroidism

Question 5

symptoms of hypothyroidism

Answer 5

constipation, weight gain, cold intolerance, edema

Question 6

after suspicion of hyper- or hypo-thyroidism, what study should be done first?

Answer 6

TSH

Question 7

how can TSH be ‘normal’ in secondary hypothyroidism?

Answer 7

with low free T4 and T3, the NORMAL response of the pituitary would be an increase in TSH. if TSH is NOT increased, it is considered to be “inappropriately normal.” the few remaining normal thyrotrophs are working as hard as they can to restore thyroid function, and the best they can do is maintain TSH within the reference range. however, it is not enough TSH to restore thyroid function

Question 8

treatment regimen for hypothyroidism

Answer 8

administer levothyroxine (T4), wait 5-6 weeks before retesting TSH levels and adjusting dose

Question 9

most common cause of hyperthyroidism

Answer 9

Graves disease

Question 10

pathogenesis of Graves disease

Answer 10

autoantibodies (IgG) stimulate TSH receptors on thyroid (hyperthyroidism, diffuse goiter), retro-orbital fibroblasts (proptosis),and dermal fibroblasts (pretibial myxedema)

Question 11

symptoms of hyperthyroidism

Answer 11

palpitations, weight loss despite increased appetite, moist skin, fine hair, pretibial myxedema, proptosis, diarrhea, heat intolerance

Question 12

what test if positive is very specific for Graves disease?

Answer 12

thyroid stimulating immunoglobulins (TSI)

Question 13

how can you distinguish between different causes of primary hyperthyroidism?

Answer 13

radioiodine uptake scan/study; Graves disease = high uptake of radiotracer in diffuse, bilateral pattern

Question 14

treatment of Graves disease and their respective mechanisms (3)

Answer 14

1. methimazole: blocks organification of iodine –> inhibits synthesis of thyroid hormones
2. PTU: same mechanism as methimazole, plus inhibits peripheral coversion of T4 to T3; reserved for pregnant patients
3. radioactive iodine: destroys hyperfunctioning thyroid tissue; contraindicated in patients with severe orbitopathy or pregnant women

Question 15

when is iodide used for hyperthyroidism?

Answer 15

preoperative period in preparation for thyroidectomy

Question 16

treatment for hyperthyroidism that shows low uptake on radioiodine uptake scan/study

Answer 16

beta-blocker (propranolol)