thyroid disease

Question 1

What is the enzyme that converts T4 to T3

Answer 1

type 1 or 2 deiodinase

Question 2

List conditions which can lead to inhibition of type 1/2 deiodinase

Answer 2

Starvation, severe illness, severe stress, neonatal period

Question 3

Cuases of increased total T3/T4

Answer 3

Hyperthyroidism/thyrotoxicosis, Increased binding proteins, increased estrogen, thyroid hormone resistance,

Question 4

Causes of increased Free T4/T3

Answer 4

Hyperthyroidism/thyrotoxicosis, thyroid hormone resistance,

Question 5

Causes of decreased total or free T4/T3

Answer 5

Hypothyroidism, decreased serum protein binding, euthyroid sick syndrome, drugs

Question 6

Best test to screen for thyroid dysfunction

Answer 6

TSH- elevated in primary hypothyroid and suppressed in primary hyperthyroid.

Question 7

When is TSH not reliable

Answer 7

If the pituitary is abnormal ie. panhypopituitarism, TSHoma, idiopathic central hypothyroidism

Question 8

Compare TSH, T4 and T3 in overt and subclinical hyperthyroidism

Answer 8

Overt: decreased TSH, elevated T3 and T4 (don’t order T3). Subclinical: decreased TSH, normal T3 and T4

Question 9

Sx of hyperthyroidism

Answer 9

nervoussness, weight loss, increased appetite (common), decreased appetite (less common), fatigue, tremor, heat intolerance

Question 10

How do you determine the cause of thyrotoxicosis

Answer 10

Thyrotoxicosis means high levels of T3/T4. If this is due to overproduction with nl to elevated iodine uptake in setting of low TSH, then it is hyperthyroidism. If this is due to high release of preformed/stored T3/T4 and iodine uptake is low, it is not true hyperthyroidism

Question 11

Causes of high uptake true hyperthyroidism

Answer 11

1. Thyrotropin receptor antibody- Graves’ disease, Hashitoxicosis. 2. Thyroid autonomy-Toxic adenoma, Toxic MNG. 3. HCG- Hydatidiform mole, Choriocarcinoma. 4. TSH- TSH-oma (pituitary tumor), Thyroid hormone resistance

Question 12

Causes of low uptake “fake” hyperthyroidism

Answer 12

1. Subacute thyroiditis- Granulomatous thyroiditis (viral), Lymphocytic thyroiditis (Postpartum thyroiditis), Amiodarone, Radiation, Palpation. 2. Ectopic thyrotoxicosis- Factitious, Struma ovarii, Functional metastatic follicular thyroid cancer

Question 13

Thyroid scan for true vs false hyperthyroidism

Answer 13

In false, thyroid will be dark so no need for scan. In true, certain areas of thyroid will light up

Question 14

pathophys of graves disease

Answer 14

B cells produce TSH reactive antibodies which bind to the TSH receptor and activate the thyroid gland, causing excess production of thyroid hormones

Question 15

Signs of Graves disease

Answer 15

thyroid eye disease, pretibial myxedema, goiter

Question 16

Graves dz treatment

Answer 16

1. meds: Antithyroid drugs (methimazole, propylthiouracil)- Inhibit synthesis of thyroid hormone. Beta blockers- Reduce systemic hyperadrenergic symptoms and effects (primarily tremor, palpitations, etc.). 2. Radioactive iodine. 3. Surgery

Question 17

Clinical course of destructive thyroiditis

Answer 17

Over 4 months, Free T4 rises and TSH drops to near 0. During this time, may need Beta blockers. Then, Free T4 drops to near 0 and TSH rises. During this time, may need levothyroxine

Question 18

Compare TSH and T4 in overt and subclinical hypothyroidism

Answer 18

Overt: elevated TSH, decreased T4. Subclinical: elevated TSH but nl free T4

Question 19

What would explain the hormone levels in subclinical hypothyroidism

Answer 19

A small decrease in free T4 causes a large increase in TSH, so that even if the T4 is still in normal range the TSH may now be out of range

Question 20

Sx of hypothyroidism

Answer 20

Mental slowness, weight gain, increased appetite, decreased appetite (more common), fatigue, muscle cramps, cold intolerance

Question 21

Etiology of hypothyroidism

Answer 21

1. Primary: Chronic autoimmne (hashimotos) thyroiditis, silent/pospartum thyroiditis (transient), subacute/granulomatous thyroiditis (transient), thyroid surgery, radioactive iodine, iodine deficiency or excess, drugs. 2. Central: pituitary tumor, truma, radiation

Question 22

list autoantibodies involved in Hashimotos thyroidits

Answer 22

TPO (thyroid peroxidase), Tg (thyroglobulin)

Question 23

Pathophys of hashimotos thyroiditis

Answer 23

B cells produce autoantibodies that destroy thyroid cells. Also CTLs induce apoptosis

Question 24

When to treat hypothyroidism

Answer 24

Normal TSH is 0.4-4.0. Almost all thyroidologists would treat with a TSH > 10mU/L. Whether to treat with a TSH between 5-10 mU/L is very controversial

Question 25

What is myxedema coma

Answer 25

An extreme form of hypothyroidism, so severe as to readily progress to death unless diagnosed promptly and treated vigorously