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DEMS Unit 3 > Thyroid disease > Flashcards

Thyroid disease Flashcards

1
Q

What enzyme converts T4 to T3?

A

Type 1 or 2 Deiodinase

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2
Q

Type 3 deiodinase

A

Removes iodine from T3 and makes reverse T3 (inactive)

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3
Q

What types of things can inhibit Type 1 or 2 Deiodinase?

A

T4 cannot be converted to T3

  1. Starvation
  2. Severe illness
  3. Severe stress
  4. Neonatal period
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4
Q

Half life of T4 and T3

A

T4: 7 days
T3: 1 day

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5
Q

Causes of increase total T3 and T4

A
  1. Hyperthyroidism/Thyrotoxicosis
  2. Increased binding proteins
    - Estrogen: acts on liver and stim TBG and albumin production - binds more T3 and T4
  3. Thyroid H resistance
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6
Q

Causes of decreased total T4 and T3

A
  1. Hypothyroidism
  2. Decreased serum protein binding
  3. Euthyroid sick syndrome
  4. Drugs
  5. Liver or kidney disease
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7
Q

TSH nl range

A

0.4-4.0

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8
Q

Thyroid hormone axis

A

D2, T4–>T3, at hypothalamus secretes TRH –>
Ant pit secretes TSH –>
Thyroid releases T3 + T4

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9
Q

TSH significance

  • when is it elevated?
  • when is it suppressed?
A
  1. Single best test to screen for thyroid dysfxn
  2. Indicates indiv. TH “set points”
  3. TSH stimulates Iodine uptake into thyroid follicular cells and TH production

Elevated: in primary HYPOthyroidism
Suppressed: in primary HYPERthyroidism

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10
Q

Sx of hyperthyroidism

A
  1. Nervousness
  2. Weight loss
  3. Increased appetite
  4. Fatigue
  5. Tremor
  6. Heat intolerance

other:
- Palpitations, hyperdefecation, trouble sleeping, diaphoresis

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11
Q

Which should you not order? TSH, Free T4, Free T3

A

Free T3

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12
Q

Thyrotoxicosis

  • What
  • TSH, free T4 + T3 levels
  • Two causes
A

High circulating lvls of TH (various causes)
Serum TSH is low
Free T4 and total T3 are elevated

Overproduction of T4+T3: suggestive of hyperthyroidism

High release of PREFORMED T4 and T3:
no true hyperthyroidism

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13
Q

If TSH is suppressed, should the thyroid gland take up Radioactive iodine?

A

no - if it does, it indicates HYPER thyroidism

TSH is low: no stimulus to take up iodine

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14
Q

TSH fxn

A

stimulates the thyroid to take up iodine

and

synthesize T4 and T3

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15
Q

In thyrotoxicosis, should TSH be high or low?

A

Low: the hypothalamus and pit “sense” elevated T4 and T4 and secretion of TRH and TSH is suppressed

  • if TSH is suppressed, there should be no uptake of iodine
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16
Q

A nl or elevated Iodine uptake in the setting of a LOW TSH indicates:

A

indicates autonomous production of thyroid hormone

- true hyperthyroid state

17
Q

If the uptake of iodine is low in the setting of a low TSH (appropriately so), what could TH excess be due to?

A

High release of preformed TH

18
Q

Low uptake Hyperthyroidism

A
  1. Subacute thyroiditis
    - granulomatous thyroiditis (viral)
  2. Chronic lymphocytic thyroiditis
  3. Radiation-induced thyroiditis
  4. Infectious thyroiditis
  5. Drug induced thyroiditis
  6. Ectopic thyrotoxicosis
19
Q

High uptake hyperthyroidism

A
  1. Thyrotropin receptor antibody
    - Graves
  2. Thyroid autonomy
    - toxic adenoma
    - toxic multinodular goiter (MNG)
  3. HCG
  4. TSH
20
Q

Graves disease has ______ autoantibodies against the TSH receptor

A

Thyroid stimulating Immunoglobulin

–> causes high uptake Hyperthyroiditis

21
Q

Common locations for Graves disease findings

A

Due to deposition of glycosaminoglycan behind eyes and in dermis over shins

  1. Opthalmopathy
  2. Pretibial Myxedema
22
Q

Treatment for Graves disease

A
  1. drugs:
    - Antithyroid H drugs: methimazole, propylthiouracil
    - Beta blockers: reduce systemic hyperadrenergic symptoms and effects
  2. Radioactive Iodine
  3. Surgery
23
Q

How do you determine the cause of thyrotoxicosis if there is no true TH production?

A

If pt has thyroid autoimmune damage –> release a ton of preformed TH –>
Body senses and drops TSH levels –>
Body reaches thyrotoxic phase
- antithyroid drugs done work since it inhibits TH SYNTHESIS, (not the case here)

Eventually T4 levels fall –>
Body senses and increases TSH –>
Body cant make more T4 –> Hypothyroid phase

24
Q

Symp of hypothyroidism

A
  1. mental slowness
  2. weight gain
  3. decreased appetite
  4. Fatigue a (non specific)
  5. muscle cramp
  6. cold intolerance
25
Q

Etiology of hypothyroidism

A
  1. Chronic autoimmune (Hasimoto’s) thyroiditis
  2. Transient hypothyroidism
  3. Iatrogenic
  4. Pituitary tumor (secondary)
26
Q

Hashimoto’s Thyroiditis
:
thyroid autoantibodies

A
  1. TPO (thyroid peroxidase)

2. Tg (thyroglobulin)

27
Q

How to treat a pt with a TSH >10 mIU/L?

A

Nl TSH is 0.4-4.0

So treat with levothyroxine (synthetic T4) –> body (-) feedbacks and reduces TSH

DEMS Unit 3 (26 decks)

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