Physiology-Hyper & Hypothyroidism

Question 1

Homeostatic loop of thyroid hormones

Answer 1

Hypothalamus secretes TRH -> Pituitary secretes TSH -> Thyroid releases T4 and T3 -> T4 converted to T3 in peripheral site -> small changes in T4 and T3 reciprocally inhibits TSH by 10-fold

Question 2

Which thyroid hormone has a higher unbound serum fraction

Answer 2

T3. Although T4 is higher total, it is mostly bound

Question 3

Tests to directly assess thyroid function

Answer 3

I-131, TSH stimulation test and perchlorate discharge test

Question 4

I-131 uptake test is best for which type of thyroid disease?

Answer 4

Hyperthyroidism. In Grave’s uptake will be increased. In exogenous causes, uptake will be absent. In hypothyroidism there still may be uptake.

Question 5

Tests to indirectly assess thyroid function

Answer 5

Serum TSH and TRH stimulation test

Question 6

Diagnosing thyroid disease

Answer 6

Thyroid scan, sonography and x-ray

Question 7

Which is most likely cancerous?

Answer 7

The “cold” nodule on the left. Cancer cells are mutated and do not take up iodine, unlike the “hot” nodule on the right that is causing hyperthyroidism

Question 8

TRH deficiency

Answer 8

Hypothalamic disease

Question 9

TSH deficiency

Answer 9

Pituitary tumor or destruction

Question 10

Causes of hypothyroidism from thyroid destruction

Answer 10

Chronic inflammation (Hashimoto’s thyroiditis, pernicious anemia, Myasthenia gravis), surgery, radioactive iodine and irradiation of neck.

Question 11

Causes of hypothyroidism from thyroid deficiency

Answer 11

Iodine deficiency, iodine excess (interferes with hormone release), antithyroid drugs (to include lithium) and biosynthetic defects

Question 12

Causes of congenital hypothyroidism

Answer 12

Thyroid dysgenesis, errors in hormone synthesis, HPT abnormalities, in utero iodine deficiency, transplacental passage of ATD and peripheral resistance to hormone

Question 13

Iodine excess

Answer 13

Can cause hyper or hypothyroidism depending on the circumstance. Hyperthyroidism if the person already has a goiter that is TSH independent. Hypothyroidism if no goiter because iodine excess blocks organification and in some people the Na-I symporter fails to shutdown and organification remains blocked due to high iodine levels.

Question 14

Hereditary defects that cause goiters

Answer 14

Iodide transport, organification, deiodinase, coupling, thyroglobulin and TSH defects. TSH and thyroid hormone resistance. Pendred’s syndrome (deafness and congenital hypothyroidism)

Question 15

Pathophysiology of Grave’s disease

Answer 15

Autoantibodies (IgG) bind to TSH receptor and continually stimulate release of thyroid hormone from the thyroid gland

Question 16

Why people get bug eyes with Grave’s disease

Answer 16

TSH receptors are present on the periorbital fat and extra ocular muscles. They get stimulated by the autoantibodies and release interferons and cytokines that cause them to swell.

Question 17

Classic triad of Grave’s disease

Answer 17

Goiter, thyrotoxicosis and opthalmopathy

Question 18

Thyroid diseases associated with this condition?

Answer 18

Grave’s and Hashimoto’s are both associated with vitiligo (development of autoantibodies against skin pigment)

Question 19

Early graying of the hair in people with hyperthyroidism

Answer 19

Canites

Question 20

Why are babies at risk for asphyxiation when a mother has thyroid disease?

Answer 20

If the mother has Grave’s, the IgG autoantibodies can cross the placenta and make the baby’s thyroid into a huge goiter

Question 21

Treatment for Graves

Answer 21

Radioactive iodine, anti-thyroid medications or surgery

Question 22

Common antithyroid drugs

Answer 22

Tapazole, methimazole, propylthiouracil (PTU), lithium, update and resins

Question 23

How do antithyroid drugs work?

Answer 23

Reduce T4 synthesis, block conversion of T4 to T3 (PTU) or deplete intrathyroidal iodine

Question 24

Antithyroid drugs to use in pregnancy

Answer 24

PTU during 1st trimester, then methimazole