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Endocriknowlogy > Thyroid: Hypothyroidism > Flashcards

Thyroid: Hypothyroidism Flashcards

1
Q

What is the most common cause of hypothyroidism worldwide?

A

Iodine deficiency

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2
Q

What is the most common cause of hypothyroidism in areas of iodine sufficiency?

A

Autoimmune disease (Hashimoto’s thyroiditis) and iatrogenic causes (treatment of hyperthyroidism)

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3
Q

What is the most common cause of neonatal hypothyroidism?

A

Thyroid gland dysgenesis (80-85%)

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4
Q

What are the genetic causes of congenital hypothyroidism?

A

PROP-1 - Combined pituitary hormone deficiencies with preservation of adrenocorticotropic hormone

PIT-1 - Combined deficiencies of growth hormone, prolactin, thyroid stimulating hormone

TSH beta - TSH deficiency

TTF-1 - Variable thyroid hypoplasia

TTF-2 Thyroid agenesis

PAX-8, NKX2-1, NKX2-5 - Thyroid dysgenesis

TSH-receptor, G S alpha (Albright hereditary osteodystrophy) - Resistance to TSH

Na+/I- symporter - Inability to transport iodide

DUOX2, DUOXA2 - Organification defect

Thyroid peroxidase - Defective organification of iodide

Thyroglobulin - Defective synthesis of thyroid hormone

Pendrin - Pendred syndrome: sensorineural deafness and partial organification defect in thyroid

Dehalogenase 1 - Loss of iodide reutilization

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5
Q

What is Pendred syndrome?

A

It is an autosomal recessive condition caused by a defect in pendrin, that is characterized by sensorineural deafness and partial organification defect in thyroid

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6
Q

Initial dose of treatment in congenital hypothyroidism

A

10-15 mcg/kg per day (dose is adjusted by close monitoring of TSH levels)

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7
Q

What are the different classifications of autoimmune hypothyroidism?

A

Hashimoto’s or goitrous thyroiditis

Atrophic thyroiditis - minimal residual thyroid tissue which is usually the end stage of Hashimoto’s thyroiditis

Subclinical hypothyroidism - phase of compensation when normal thyroid hormone levels are maintained by a rise in TSH; may have minor symptoms

Clinical or Overt hypothyroidism - unbound T4 levels fall and TSH levels rise further; more readily apparent symptoms; usually TSH >10 mIU/L

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8
Q

Prevalance of autoimmune hypothyroidism: Sex, Race, Age

A

Sex: Women

Race: Japanese

Age: 60 years

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9
Q

What are the best documented genetic risk factors for autoimmune hypothyroidism?

A

HLA-DR polymorphisms (especially HLA-DR3, DR4, DR5 in Caucasians)

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10
Q

How does the following affect the risk of autoimmune hypothyroidism?

High iodine intake

Low selenium intake

Decreased exposure to microorganisms in childhood

Smoking cessation

Alcohol intake

A

High iodine intake - increased risk

Low selenium intake - Increased risk

Decreased exposure to microorganisms in childhood - Increased risk

Smoking cessation - Increased risk

Alcohol intake - Decreased risk

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11
Q

Thyroid cell destruction is primarily mediated by __________

A

CD8+ cytotoxic T cells

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12
Q

Microscopic findings in Hashimoto’s thyroiditis

A

Marked lymphocytic infiltration of the thyroid with germinal center formation, atrophy of the thyroid follicles accompanied by oxyphil metaplasia, absence of colloid, and mild to moderate fibrosis

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13
Q

TRUE OR FALSE: Transplacental passage of Tg or TPO antibodies has no effect on the fetal thyroid.

A

TRUE

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14
Q

Myxedema is caused by increased dermal ________

A

Increased dermal glycosaminoglycan content that traps water –> skin thickening without pitting

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15
Q

Effect of hypothyroidism on prolactin

A

Prolactin levels are often modestly increased –> alterations in libido, fertility, galactorrhea

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16
Q

How do you define Hashimoto’s encephalopathy?

A

It is a steroid-responsive syndrome associated with TPO antibodies, myoclonus, and slow-wave activity on EEG.

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17
Q

Effect of hypothyroidism on pituitary gland

A

Pituitary gland may be enlarged due to thyrotroph hyperplasia

18
Q

Most frequent symptoms of hypothyroidism

A

Tiredness and weakness

19
Q

Most frequent signs of hypothyroidism

A

Dry coarse skin; cool peripheral extremities

20
Q

In autoimmune hypothyroidism, __% of circulating unbound T3 levels are normal.

A

25% (therefore T3 measurements are not indicated)

21
Q

TRUE OR FALSE: A normal TSH level excludes both primary and secondary hypothyroidism.

A

FALSE. A normal TSH level excludes primary, but not secondary, hypothyroidism.

If TSH is elevated - measure FT4

If TSH is normal - check if pituitary disease is suspected

22
Q

Better measure of thyroid function in the months following radioiodine treatment - FT4 or TSH?

A

FT4

23
Q

Target T4 levels in secondary hypothyroidism - high normal or low normal?

A

T4 levels at the upper half of reference interval (TSH levels cannot be used to monitor therapy)

24
Q

Drugs that can cause hypothyroidism

A

Amiodarone

Lithium

25
Q

Daily replacement dose of levothyroxine

A

1.6 mcg/kg BW

26
Q

Goal TSH in the treatment of clinical hypothyroidism

A

Normal TSH, ideally in the lower half of the reference range

27
Q

When to recheck TSH after instituting treatment for hypothyroidism

A

2 months after instituting treatment or after any subsequent change in levothyroxine dosage

28
Q

How many months before patients experience full relief from symptoms?

A

3-6 months after normal TSH levels are restored

29
Q

Levothyroxine dosage is adjusted by which increments

A

12.5 to 25 mcg increments

30
Q

What to do if patient misses a dose of T4?

a. Take missed dose before the next day
b. Take two doses of skipped tablets at once
c. Just take the dose for the next day

A

Because T4 has a long half-life (7 days), patients who miss a dose can be advised to take 2 doses of the skipped tablets at once.

31
Q

Drugs that can affect levothyroxine absorption

A

Oral estrogen containing medications or SERM
Bile acid sequestrants, ferrous sulfate, calcium supplements, sevelamer, sucralfate, proton pump inhibitors, lovastatin, aluminum hydroxide, rifampicin, amiodarone, carbamazepine, phenytoin, tyrosine kinase inhibitors

32
Q

When to treat subclinical hypothyroidism?

A
  1. If a woman wishes to conceive or is pregnant
  2. When TSH levels >10 mIU/L
  3. If TSH levels <10:
    a. Suggestive symptoms of hypothyroidism
    b. Positive TPO antibodies
    c. Any evidence of heart disease

(Must confirm that any elevation of TSH is sustained over a 3-month period before treatment is given)

33
Q

Levothyroxine dose in subclinical hypothyroidism

A

25-50 mcg/d (with the goal of normalizing TSH)

34
Q

Prior to conception, levothyroxine therapy should be targeted to maintain a serum TSH in the normal range but

A

<2.5 mIU/L

35
Q

In pregnancy, levothyroxine dose may need to be increased by up to __%.

A

45%

36
Q

Elderly patients may require __% less thyroxine than younger patients.

A

20%

37
Q

TRUE: Hypothyroid patients must achieve euthyroidism before undergoing emergency surgery.

A

FALSE. Emergency surgery is generally safe in patients with untreated hypothyroidism, although routine surgery in a hypothyroid patient should be deferred until euthyroidism is achieved.

38
Q

What is the major pathogenesis in myxedema coma?

A

Hypoventilation which leads to hypoxia and hypercapnia (usually precipitated by factors that impair respiration)

39
Q

TRUE OR FALSE: T3 is routinely given in combination with T4 in treating hypothyroidism.

A

FALSE

40
Q

TRUE OR FALSE: T3 may be added to T4 in treating myxedema coma.

A

TRUE, because T4 to T3 conversion is impaired in myxedema coma.

41
Q

In myxedema coma, external warming is indicated only if the temperature is ___.

A

<30 degrees Celsius (as it can result in cardiovascular collapse)

42
Q

TRUE OR FALSE: Parenteral hydrocortisone should be administered in myxedema coma, because there is impaired adrenal reserve in profound hypothyroidism.

A

TRUE

Endocriknowlogy (9 decks)

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