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Flashcards in thyroid disease Deck (25):

What is the enzyme that converts T4 to T3

type 1 or 2 deiodinase


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

Starvation, severe illness, severe stress, neonatal period


Cuases of increased total T3/T4

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


Causes of increased Free T4/T3

Hyperthyroidism/thyrotoxicosis, thyroid hormone resistance,


Causes of decreased total or free T4/T3

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


Best test to screen for thyroid dysfunction

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


When is TSH not reliable

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


Compare TSH, T4 and T3 in overt and subclinical hyperthyroidism

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


Sx of hyperthyroidism

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


How do you determine the cause of thyrotoxicosis

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


Causes of high uptake true hyperthyroidism

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


Causes of low uptake "fake" hyperthyroidism

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


Thyroid scan for true vs false hyperthyroidism

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


pathophys of graves disease

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


Signs of Graves disease

thyroid eye disease, pretibial myxedema, goiter


Graves dz treatment

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


Clinical course of destructive thyroiditis

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


Compare TSH and T4 in overt and subclinical hypothyroidism

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


What would explain the hormone levels in subclinical hypothyroidism

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


Sx of hypothyroidism

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


Etiology of hypothyroidism

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


list autoantibodies involved in Hashimotos thyroidits

TPO (thyroid peroxidase), Tg (thyroglobulin)


Pathophys of hashimotos thyroiditis

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


When to treat hypothyroidism

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


What is myxedema coma

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