Hypothyroidism Flashcards

1
Q

What is the difference in primary and secondary hypothyroidism? what is the commonest cause of hypothyroidism?

A

Primary - failing thyroid:
-low T3 and T4
-high TSH
(in primary subclinical hypothyroidism - TSH high but T3 and T4 normal)

Secondary - pituitary gland fail:

  • low T3 and T4
  • low TSH
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2
Q

How are the causes of primary hypothyroidism classified into 3 different classifications?

A

Goitrous: Hashimotos thyroiditis mainly, iodine deficiency
(also hereditary biosynthetic defects, maternally transmitted, drug induced)

Non-goitrous: atrophic thyroditis, congenital developmental defect, post surgery, post-radio iodine ablation, post radiation e.g. lymphoma

Self-limiting: following withdrawal suppressive thyroid therapy, subacute thyroiditis and chronic thyroiditis with transient hypothyroiditis, post-partum thyroiditis

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3
Q

What are the causes for secondary hypothyroidism?

A

Hypothalamic: congenital, infection (encephalitis), inflitration (sarcoidosis), malignancy (craniopharyngoma)

Pituitary: panhypopituitarism

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4
Q

What is hashimotos thyroiditis? what is it characterised by? what antibodies are seen?

A
  • most common cause of hypothyroidism
  • autoimmune destruction of thyroid gland

Characterised by:

  • presence of thyroid peroxidase antibodies in blood
  • T cell infiltration and inflammation on microscopy

Other antibodies?

  • anti thyroglobulin antibodies (60%)
  • TSH Rabs - blocking them (10-20%)
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5
Q

What is the epidemiology of hashimotos thyroiditis?

A
  • middle aged women (45-60yrs)

- other AI disease

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6
Q

S/S hypothyroidism:

  • skin/hair
  • thermogenesis
  • fluid retention
  • cardiac
  • metabolic
  • GI
  • resp.
  • CNS
  • Gynae
A

-skin/hair: coarse/dry/periorbital puffiness/pale/cool/doughy skin

  • thermogenesis: intolerance to cold
  • fluid retention: pitting oedema
  • cardiac: bradycardia/cardiac dilatation/ pericardial effusion/worsening of heart failure
  • metabolic: hyperlipideamia, decreased appetitis, wt gain
  • GI: constipation
  • resp.: deep/hoarse voice, macroglossia, obstructive sleep apnoea
  • CNS: tired/decreased motor activities/peripheral neuropathy/prolongation of tendon jerks/carpal tunnel syndrome/ decreased visual acuity
  • Gynae: menorrhagia, later oligo- or amenorrhea, hyperprolactinaemia
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7
Q

What other lab investigations are important for hypothyroidism?

A
  • macrocytosis is typical
  • elevated creatinine kinase
  • hyperlipidaemia
  • hyponatraemia (reduced renal tubular water loss)
  • hyperprolactinaemia
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8
Q

How is hypothyroidism managed?

A

-normal metabolic rate has to be restored gradually

Younger patient:
-thyroxine at 50-100nanograms daily

Elderly/hx of IHD:
-25-50nanograms daily

adjust every 4 weeks according to response

  • check TSH 2 mths after dose change
  • once established check TSH every 12-18mths
  • dose requirements may increase 25-50% in pregnancy
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9
Q

What is a myxoedema coma? who does this typically effect? what is found on ECG and ABG?

A

Severe hypothyroidism - usually effects women with longstanding but frequently unrecognised or untreated hypothyroidism (up to 60% mortality)

ECG:

  • bradycardia
  • low voltage complexes
  • varying degress of heart block
  • T wave inversion
  • Prolongation of QT interval

ABG: type 2 resp. failure

  • hypoxia
  • hypercarbia
  • resp. acidosis

(co-existing adrenal failure in 10% patients)`

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10
Q

What is the treatment for myxoedema coma?

A

ICU

  • passively and slowly rewarm
  • cardiac monitoring
  • monitor BP, CVP, oxygenation, urine output, blood glucose levels
  • fluids/fluid restrict/electrolyte balance
  • broad spec. abiotics
  • thyroxine cautious
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11
Q

What is amiodarone induced thyroid dysfunction?

  • what proportion of patients are affected?
  • how does this affect thyroid?
A

50% pts.

  • thyrotoxicosis more frequently if low iodine intake
  • hypothyroid more frequently if high iodine intake
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