Thyroid Disorders

Question 1

Normal thyroid weight

Answer 1

25 grams

Question 2

Production of T4 and T3

Answer 2

T4 is produced completely by the thyroid

20% of T3 is produced by the thyroid, the rest is made by peripheral conversion

Question 3

T4 half-life

Answer 3

1 week, check q 5-6 weeks

Question 4

T3 half-life

Answer 4

1 day, check q 2 weeks

Question 5

TSH range by trimester

Answer 5

1st trim - 0.1 - 2.5 mlU/L
2nd trim - 0.2 - 3.0 mlU/L
3rd trim - 0.3 - 3.0 mlU/L

Question 6

1st trimester TSH changes

Answer 6

high hCG levels may stim thyroid T4 to suppress the serum TSH to 0.03 to 0.5 mU/L in up to 15% of women

Question 7

Pregnancy changes - TBG and TT4/TT3

Answer 7

Increased due to increasing estrogen, basal levels increase 2-3 fold. As a result, TT4 & TT3 levels increase by 50%

Question 8

What is the function of placental type II deiodinase?

Answer 8

Converts T4 to T3

Question 9

What is the function of type III deiodinase?

Answer 9

Converts T4 to reverse T3, which is metabolically inactive

Question 10

Fetal hormone concentrations at 12w

Answer 10

TT4 - 2 ug/dL
FT4 - 0.1 ng/dL
FT3 - 6 ng/dL
TSH - 4 mU/L

Question 11

Fetal hormone concentrations at term

Answer 11

TT4 - 10 ug/dL
FT4 - 1.5 ng/dL
FT3 - 45 ng/dL
TSH - 8 mU/L

Question 12

Definition of subclinical hyperthyroidism

Answer 12

TSH <0.1 mU/L with normal FT4 and free triiodo- thyronine (FT3), in the absence of nonthyroidal illness.

Question 13

MCC of hypothyroidism

Answer 13

Hashimoto thyroiditis (goiter + antithyroglobulin ab + antithyroid peroxidase ab

Question 14

Complications of untreated hypothyroidism

Answer 14

SAB
GHTN
Preeclampsia
Abruption
LBW
Prematurity
Stillbirth

Question 15

Goal of treatment - hypothroidism

Answer 15

TSH 0.5 - 2 mU/mL, FT4 in upper third of nl range (nl range 0.89 - 1.76 ng/dL @ UCH)

Question 16

Dosing - hypothyroidism

Answer 16

100 - 150 mcg of T4, adjusted q 4w. If already dx’d prepregnancy, may need increase at 5w

Question 17

FeSO4 and T4

Answer 17

FeSO4 interferes with thyroxine absorption

Question 18

Ddx of goiter in pregnancy

Answer 18

Iodine deficiency (WHO recs 150 ug/d adults, 250 ug/d pregnant)
Graves (95% of hyperthyroidism in pregnancy)
Hashimoto thyroiditis
Excessive iodine intake
Lymphocytic thyroiditis
Thyroid cancer
Lymphoma
Lithium or thionamide therapy

Question 19

Complications of untreated hyperthyroidism

Answer 19

SAB
PTB
Preeclampsia
Fetal death
Abruption
FGR
Neonatal Graves’
Maternal CHF
Thyroid storm

Question 20

Goals of treatment - hyperthyroidism

Answer 20

Maintain maternal free T4 in the high-normal range (nl range 0.89 - 1.76 ng/dL @ UCH), TSH less than 0.5 mU/mL. In many pts, MMI can be d/c’d by 32-36w, bc remission of Graves during pregnancy is common, often w/ relapse after delivery.

Question 21

Dosing - hyperthyroidism

Answer 21

• Initial doses: MMI 5-15 mg/d, PTU 50-300 mg/d in divided doses (Barbour – mild 150 mg/d, mod 300 mg/d, severe 600)
• After pt is euthyroid, the dose of PTU should be tapered/halved, with further reduction as pregnancy progresses
• Equivalent doses of PTU to MMI are 10:1 to 15:1 (100 mg PTU = 7.5 to 10 mg MMI)
• MMI, PTU cross the placenta; both safe for breastfeeding

Question 22

PTU side-effects

Answer 22

Rash (5%)
Pruritis
Drug-related fever
Hepatitis
Lupus-like syndrome
Agranulocytosis (0.1%)

Question 23

B-blockers in hyperthyroidism

Answer 23

Treat hyperadrenergic sx only until euthyroid, bc long-term tx has been assoc with FGR. Metoprolol or propranolol usu favored over atenolol.

Question 24

Placental transfer of thyroid hormone

Answer 24

Maternal FT3 and FT4 cross starting early in gestation, TSH does not cross the placenta

Question 25

TSI & TRAB, and the fetus

Answer 25

• Immunoglobulin G (IgG) TSH receptor-stimulating antibodies (thyroid-stimulating immunoglobulins [TSI] and TSH receptor antibodies [TRAB]) cross placenta as early as 18 to 20w when levels are at least 2.5-fold elevated.
• TRAb present in over 95% of pts with active Graves, if > 3x nl then close follow up of fetus. -Some recommend testing in 1st trimester, then repeat at 22-26w, others prefer one test at 24-28 bc of the normal decline in ab concentration, which starts at approx 20w.

Question 26

Manifestations of fetal hyperthyroidism

Answer 26

Fetal tachycardia, fetal goiter, advanced bone age, poor growth, craniosynostosis. Cardiac failure and hydrops with severe disease

Question 27

When to FNA thyroid nodules

Answer 27

• Sono features of malignancy (microcalcifications, hypoechoic patterns, irregular margins, elongated nodules, intranodular vascularity
• High or normal serum TSH
• Solid thyroid nodules larger than 1 cm, complex nodules 1.5 to 2 cm
• Nodules 5 mm to 1 cm if high-risk famhx (MEN 2, familial papillary thyroid carcinoma, familial polyposis, familial medullary carcinoma)
• High-risk personal hix (rapid onset or growth of nodule, hx of head and neck irradiation during childhood, hoarseness, persistent cough)
• Nodules discovered in the last month of pregnancy could reasonably have FNA delayed until after delivery

Question 28

What to do about a thyroid nodule + suppressed TSH

Answer 28

• May be a warm or hot nodule. Warm or hot nodules are rarely malignant but are often nondx on FNA.
• Perform a radioisotope scan postpartum to determine whether the nodule is warm or cold before obtaining an FNA.

Question 29

Thyroid nodules - risk of malignancy

Answer 29

-Differentiated thyroid cancer has been found in 5% to 40% of biopsies.

Question 30

Most common malignancy in thyroid nodules

Answer 30

Papillary thyroid carcinoma.

Question 31

Treatment of thyroid storm in pregnant women

Answer 31

-PTU 600–800 mg orally, immediately, even before labs are back; then 150–200 mg PO q 4–6 hrs. If not takin PO, use MMI PR.
-Starting 1–2 hr after PTU, saturated solution of potassium iodide (SSKI), 2–5 drops PO q 8 hrs; or sodium iodide, 0.5–1.0 g IV q 8 hrs; or Lugol’s solution, 8 drops q 6 hrs; or Lithium carbonate, 300 mg PO q 6 hr.
-Dexamethasone, 2 mg IV or IM q 6 hr x 4 doses.
-Propranolol, 20–80 mg PO q 4-6 hrs, or 1-2 mg IV q 5 min for total of 6 mg, then 1-10 mg IV q 4 hrs.
-If history of severe bronchospasm:
Reserpine, 1–5 mg IM q 4–6 hrs.
Guanethidine, 1mg/kg PO q 12 hrs.
Diltiazem, 60 mg PO q 6–8 hrs.
-Phenobarbital, 30–60 mg PO q 6–8 hrs prn extreme restlessness.

Question 32

nl FT4 range

Answer 32

0.89 - 1.76 ng/dL (UCH)

Question 33

nl TT3 range

Answer 33

60 - 181 ng/dL (UCH)

Question 34

nl TT4 range

Answer 34

4 - 11 ug/dL (UCH). Per Creasy, the nl reference range for TT4 should be adjusted by a factor of 1.5 in pregnant patients (bc of increased TBG).

Question 35

Why do we follow FT4, but total T3?

Answer 35

I think bc T4 is more tightly bound to TBG, so TT4 is high in pregnancy, and FT4 is more accurate, whereas T3 is less tightly bound.