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thyroid disorders Flashcards

1
Q

negative feedback loop for thyroid

A
  • hypothalamus detect low circulating TH -> release TRH -> TRH instruct pituitary gland to release TSH -> TSH instruct thyroid gland to secrete TH
  • hypothalamus detect elevated TH -> stop releaseing TRH
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2
Q

types of antibodies for autoimmunity test

A

1) ATgA: thyroglobulin antibodied
2) TPO: thyroperoxidase antibodies
3) TRAb: thyrottrppin receptor IgG Ab

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3
Q

indication for screening thyroid disorder

A

1) autoimmune disease
2) 1st degree relative
3) psychiatric disorder
4) amiodarone/lithium
5) Hx of head, neck radiation for malignancies
6) S&S of hypo/hyperthyroidism
7) new onset AF

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4
Q

possible causes of primary hypothyroidism

A

1) iodine deficiency
2) Hashimoto disease

  • +ve ATgA & TPO antibodies
  • disproportionately affect women

3) Iatrogenic

  • thyroid resection
  • radioiodine ablative therapy for hyperthyroidism
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5
Q

causes of secondary hypothyroidism

A

1) central hypothyroidism

  • hypothalamus X TRH, pituitary gland X TSH

2) drug induced

  • amiodarone, lithium
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6
Q

causes of tertiary hypothyroidism

A

hypothalamus X producing TRH

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7
Q

S&S hypothyroidism

A
  • cold intolerance, dry skin, course hair
  • lethargy, fatigue, weakness
  • weight gain
  • bradycardia, hypotension
  • slow reflexes
  • periorbital swelling
  • menstrual disturbances
  • goiter
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8
Q

clinical manifestations of hypothyroidism

A
  • increase cholesterol, LDL, TG
  • increase atherosclerosis & MI risk
  • increase CPK
  • increase miscarriage risk
  • impaired fetal cognitive development
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9
Q

lab test for hypothyroidism

A

1) primary

  • increase TSH, decrease T4
  • +ve TPO, ATgA (autoimmune)

2) central

  • decrease TSH, decrease T4
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10
Q

hypothyroidism - levothyroxine - dosage

A

1) initial

  • young healthy adult: 1.4 mcg/kg/day
  • 50-60 yo + X cardiac issue: 50 mcg daily
  • CVD: 12.5-15mcg/day

2) titration

  • increase/decrease 12.5-25mcg/day increment or 10-15% weekly dose
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11
Q

hypothyroidism - levothyroxine - dosing instruction

A

1) 30-60 mins before bfast or 4 hrs after dinner
2) food decrease absorption, can only take water, 2 hrs apart from divalent supplement & antacid

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12
Q

hypothyroidism - levothyroxine - PK

A

1) absorption

  • oral, absorbed duodenum & jejunum

2) distribution

  • highly plasma protein bound

3) metabolism

  • liver (glucuronidation, sulphation, deiodination)

4) elimination

  • kidneys, metabolite urine & faeces
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13
Q

hypothyroidism - levothyroxine - AE

A

1) reduced appetite
2) anxiety, trouble sleeping
3) Diarrhoea
4) hair loss
5) rare & serious

  • heart issue (arrhythmia, high GP, pain, failure)
  • seizure
  • myxoedema
    ** reduce blood flow to GI -> affect gut absorption of oral levothyroxine
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14
Q

hypothyroidism - levothyroxine - monitoring

A
  • target TSH 0.4 - 4 mIU/L
  • 4 - 8 wks assess response after initiate/change therapy
  • if normal FT4 but elevated TSH = non adherence
  • monitor FT4 instead of TSH if central hypothyroidism
  • thyroid function test (tFT)
    ** 6 - 12 month for non pregnant after euthyroid state
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15
Q

hypothyroidism - levothyroxine - CI

A

heart problem, epilepsy, hyperthyroidism

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16
Q

hypothyroidism - liothyronine - what is it

A

synthetic T3

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17
Q

hypothyroidism - liothyronine - indications

A

1) myxoedema coma
2) if T4 X work
3) combine w T4 if normalised TSH but still complain of hypothyroidism symptoms
4) need drug to wear off quickly (pre thyroid surgery)

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18
Q

hypothyroidism - liothyronine - dose

A
  • normal: 25mcg
  • elderly/CVD: 5mcg
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19
Q

effect of maternal hypothyroidism in pregnancy

A
  • miscarriage, spontaneous abortion
  • congenital defect, impaired cognitive development
20
Q

transfer of TH from mother to child

A

maternal TH provide fetus up to 12 wks before fetus develop 1 thyroid gland

21
Q

effect of pregnancy on dosage for hypothyroidism

A

increase dose by 30-50% to maintain euthyroid status

22
Q

monitoring target for TSH for pregnancy and hypothyroidism

A

1) 1st trimester: < 2.5 mIU/L
2) 2nd trimester: < 3.0 mIU/L
3) 3rd trimester < 3.5 mIU/L

23
Q

definition of subclinical hypothyroidism

A

1) elevated TSH w normal T4
2) result of early hashimoto disease

24
Q

risks involved in subclinical hypothyroidism

A
  • TSH > 7.0 mIU/L in older adult = greater risk of HF
  • TSH > 10 mIU/L = greater risk of coronary heard disease
25
Q

when to consider treating subclinical hypothyroidism

A

1) TSH > 10 mIU/L
2) TSH 4.5 - 10 mIU/L

  • symptoms of hypothyroidism
  • TPO Ab present
  • history of cardiovascular disease, HF, HF risk factor
26
Q

subclinical hypothyroidism treatment

A

initial dose 25-75mcg

27
Q

causes of hyperthyroidism

A

1) Toxic diffuse goiter

  • TSI stimulate TH production, not under -ve feedback loop

2) pituitary adenomas
3) toxic adenoma (hot nodule): secrete T3
4) toxic multi-nodular goiter (Plummer’s disease)

  • multiple nodules that secrete T3

5) drug induced: amiodarone, lithium
6) subacute thyroiditis

  • infection, drug induced, early Hashimoto
  • released of stored hormone in follicle
28
Q

S&S of hyperthyroidism

A

(THYROIDISME)

  • tremor
  • heart rate up
  • yawning
  • restlessness
  • oligiomenorrhoea/amenorrhoea
  • irritability
  • diarrhoea
  • intolerance to heat
  • sweating
  • muscle wasting & weight loss
  • exophthalmos in Graves
29
Q

diagnosis of hyperthyroidism

A
  • S&S
  • elevated free T4 serum concentration
  • suppressed TSH concentration (except TSH-secreting adenomas)
  • readioactive iodine uptake (RAIU) for better aetiology
    ** uptake elevated if gland actively secreting TH (Graves, TSH-secreting adenoma, toxic adenoma, multi nodular goiter)
    ** uptake suppressed in disorders caused by thyroiditis/cancer
  • presence of TRAb, ATgA, TPO
  • biopsy
30
Q

treatment options for hyperthyroidism

A

1) surgery resection
2) radioactive iodine (RAI) ablative therapy
3) thyroidectomy
4) antithyroid pharmacotherapy

31
Q

surgery resection for hyperthyroidism

A

can cause hypothyroidism

32
Q

radioactive iodine (RAI) for hyperthyroidism

A
  • also result in hypothyroidism
  • first line if X CI for Graves
  • concentrate in thyroid tissue -> destroy overactive thyroid cells
  • X pregnancy
33
Q

thyroidectomy for hyperthyroidism

A

can also cause hypothyroidism

34
Q

indication for hyperthyroidism pharmacotherapy

A

1) awaiting ablative therapy/surgery

  • deplete stored hormone
  • minimise risk of post-ablation hyperthyroidism caused by thyroiditis

2) X ablative/surgical candidates or failed to normalise thyroid

3) mild disease, small goiter, low or -ve antibody titres, women
4) limited life expectancy

35
Q

pharmacotherapy options for hyperthyroidism

A

1) thionamide `
2) iodide
3) non selective beta blocker

36
Q

MOA of thionamides

A

act as substrate for TPO -> inhibit thyroid peroxidase -> inhibit thyroid hormone synthesis -> reduce thyroid hormone output -> reduce S&S of thyrotoxicosis

37
Q

dosing for thionamides

A

1) Carbimazole (more for Graves)

  • initial: 15-60mg daily in 2-3 divided doses
  • euthyroid: 5 - 15 mg once daily

2) PTU

  • initial: 50-150mg oral 3 times daily
  • euthyroid: reduce to 50mg 2-3 times daily
38
Q

thioamides AE

A

1) Rash, joint pain, N, jaundice
2) hypothyroidism

  • monitor thyroid size & serum TSH
  • titrate dose (reduce) once thyroid size reduce + TSH normalise

3) hepatotox
4) rash (SJS)
5) agranulocytosis early in therapy (3 months)
6) fever

39
Q

efficacy/monitoring for thioamide

A
  • slow onset, max effect 4-6 month (stop production but X remove stored hromone)
  • monthly dose titration
40
Q

MOA of iodides

A
  • inhibit release of stored TH
  • minimal effect on hormone synthesis
  • decrease vascularity and size of gland
41
Q

iodides indication for hyperthyroidism

A

1) before surgery (7-10 days) to shrink gland
2) after ablative therapy (3-7 days) to inhibit thyroiditis-mediated release of stored TH
3) thyroid storm

42
Q

non selective beta blockers

A
  • propanolol
  • MOA: block hyperthyroid manifestation by beta-adrenergic receptor, high dose block T4 -> T3 conversion
  • indication
    1) Symptomatic relief
    2) bridge therapy for thioamide therapy to kick in or before ablation/surgery
    3) Treatment of thyroiditis (self limiting)
43
Q

pregnancy and hyperthyroidism

A
  • symptoms: failure to gain weight despite good appetite, tachycardia
  • fetal loss if untreated but thioamide risk of embryopathy
  • treatment (lowest possible dose)

** T4 at uper limit
** 1st trimester: PTU
** 2nd and 3rd: carbimazole cuz PTU high hepatotox

44
Q

definition of subclinical hyperthyroidism

A
  • low/undetectable TSH w normal T4
45
Q

risk of subclinical hyperthyroidism

A
  • elevated risk of AF in pt > 60 yo
  • elevated risk of bone fracture in postmenopausal women
  • conflicting data about mortality risk
46
Q

treatment of subclinical hyperthyroidism

A
  • similar to over hyperthyroidism except oral therapy alternative to ablative therapy in young pt
  • compelling if TSH < 0.1 mIU/L
  • beta blocker (Esp AF)
47
Q

drugs and thyroid problem

A

1) Amiodarone

  • iodine in chemical structure
  • affect iodine uptake/secretion/production -> thyroiditis
  • hypo & hyper

2) lithium

  • hypo: inhibit thyroid hormone secretion & release -> signal increase in TSH & possible goiter development
  • hyper: thyroiditis

3) interferon alfa

  • thyroiditis: hyper -> hypo

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