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Year 3 > Hypothyroidism (E&M) > Flashcards

Hypothyroidism (E&M) Flashcards

1
Q

Define hypothyroidism.

A

Clinical state resulting from underproduction of the thyroid hormones thyroxine (T4) and triiodothyronine (T3)

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2
Q

What are some different types of hypothyroidism?

A
  • primary
  • secondary
  • sub-clinical
  • myxoedema coma
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3
Q

Define primary hypothyroidism.

A
  • most cases are due to primary hypothyroidism
  • failure of the thyroid gland to produce thyroid hormone
  • TSH concentrations above the reference range and free thyroxine concentrations below the reference range
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4
Q

Define secondary hypothyroidism.

A

Underproduction of TSH by the pituitary gland

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5
Q

Define sub-clinical hypothyroidism.

A

State of usually asymptomatic, mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH (may occur in intercurrent illness)

(Sub-clinical = not detected by usual clinical tests)

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6
Q

Define myxoedema coma.

A

Rare severe form of hypothyroidism with multi-organ failure

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7
Q

What are some congenital causes of hypothyroidism?

A
  • thyroid dysgenesis
  • inherited defects in thyroid hormone biosynthesis
  • thyroid dysplasia / aplasia
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8
Q

What are some acquired causes of hypothyroidism?

A
  • Hashimoto’s thyroiditis (autoimmune): goitre due to lymphocytic and plasma cell infiltration
  • primary atrophic hypothyroidism: diffuse lymphocytic infiltration of the thyroid –> atrophy, no goitre
  • iatrogenic: post-thyroidectomy, radioiodine, hyperthyroid medication, amiodarone, lithium, iodine
  • severe iodine deficiency (chief cause worldwide)
  • iodine excess (Wolff-Chaikoff effect)
  • thyroiditis: subacute temporary hypothyroidism after hyperthyroid phase (post-partum thyroiditis / de Quervain thyroiditis)
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9
Q

What causes secondary hypothyroidism?

A

Pituitary disorders e.g. pituitary adenoma –> TSH deficiency

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10
Q

What group does hypothyroidism occur more commonly in?

A

F > M

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11
Q

What is the most common cause of hypothyroidism worldwide?

A
  • iodine deficiency
  • in developed countries where this is not an issue, Hashimoto’s thyroiditis
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12
Q

What more serious condition is Hashimoto’s thyroiditis linked with?

A

MALT lymphoma

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13
Q

What are some risk factors for hypothyroidism?

A
  • iodine deficiency
  • female sex
  • middle age
  • Fx of autoimmune thyroiditis
  • autoimmune disorders
  • treatment for thyroid disease
  • post-partum thyroiditis
  • Turner’s and Down’s syndromes
  • radiotherapy to head and neck
  • amiodarone/lithium use
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14
Q

What are some non-specific symptoms of hypothyroidism? (4)

A
  • weakness
  • lethargy
  • depression
  • mild weight gain
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15
Q

Describe symptoms/presentations seen in the history of a patient with hypothyroidism.

A
  • insidious onset
  • cold intolerance
  • decreased sweating
  • lethargy
  • hoarse voice (due to Reinke’s oedema)
  • cramps
  • dry skin + hair loss
  • weight gain, constipation, reduced appetite
  • mental slowness, depression
  • ataxia, paraesthesia
  • menstrual disturbance (menorrhagia, irregular cycles)
  • Hx of surgery or radioiodine therapy for hyperthyroidism
  • personal/Fx of other autoimmune conditions (e.g. Addison’s, T1DM)
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16
Q

What symptoms/presentations are seen in myxoedema coma?

A
  • severe hypothyroidism usually seen in the elderly
  • hypothermia
  • hypoventilation
  • hyponatraemia
  • heart failure
  • confusion
  • coma
17
Q

What clinical features are seen on examination of a patient with hypothyroidism?

A
  • hypertension due to decreased peripheral resistance
  • hands - bradycardia, cold hands
  • head/neck/skin - pale puffy face, goitre, oedema, hair loss, dry skin, vitiligo
  • chest - pericardial effusion, pleural effusion
  • abdomen - ascites
  • neurological - slow relaxation of reflexes, signs of carpal tunnel syndrome
18
Q

What is a feature you would see in Hashimoto’s thyroiditis on examination?

A

Firm and non-tender goitre

19
Q

What is the 1st line investigation for hypothyroidism?

A
  • serum thyroid-stimulating hormone (TSH)
  • normal TSH range is 0.4 to 4.0 mIU/L and levels are elevated in primary hypothyroidism
  • in sub-clinical disease levels are only mildly elevated - usually <20mIU/L or maybe <10mIU/L
20
Q

What other investigations do we consider for hypothyroidism (after conducting 1st line serum TSH)?

A

Bedside:

  • fasting blood glucose (may be elevated in T1DM - associated with hypothyroidism)

Bloods:

  • TFTs - primary hypothyroidism (high TSH low T3/T4) vs secondary hypothyroidism (low TSH low T3/T4)
  • antithyroid peroxidase antibodies - elevated in most patients with autoimmune thyroiditis, not routinely ordered
  • FBC - normocytic anaemia associated with hypothyroidism
  • serum cholesterol - often elevated –> high CVD risk
  • U&Es - may show low sodium
21
Q

What may TFT results be during normal pregnancy?

A
  • normal TSH, fT4 and fT3 but raised total T3 and T4
  • due to high concentration of thyroid-binding globulins
22
Q

If we suspect pituitary insufficiency in a patient with hypothyroidism, what do we do next?

A

MRI

23
Q

What antibody is present in Hashimoto’s thyroiditis?

A

Anti-TPO

24
Q

What electrolyte can be affected in hypothyroidism?

A

Sodium - can get euvolaemic hyponatraemia

25
Q

What do you see in sick euthyroid syndrome?

A

Low T3/T4 and normal TSH with acute illness

26
Q

What is the diagnostic criteria for hypothyroidism?

A
  • TFTs
  • clinical
27
Q

What are some differential diagnoses for (primary) hypothyroidism?

A
  • secondary hypothyroidism - with/without other symptoms of hypopituitarism e.g. hypogonadism and secondary adrenal insufficiency, papilledema and visual field deficits, low TSH, MRI
  • depression
  • Alzheimer’s - cognitive dysfunction in hypothyroidism responds to thyroid replacement therapy
  • anaemia - hypothyroid and anaemic patients often have fatigue and dyspnoea on exertion, associated with concurrent autoimmune conditions e.g. pernicious anaemia, TSH
28
Q

What is the 1st line treatment for primary hypothyroidism in healthy patients <65?

A

Levothyroxine

  • 1.6mg/kg/day orally adjust dose in increments of 12.5 to 25mg to normalise TSH
  • 50-100mg/day
  • adjust dose to TFTs but do not suppress
  • important to rule out underlying adrenal insufficiency before starting thyroid replacement therapy - can precipitate Addisonian crisis
  • lifelong
29
Q

What is the 1st line treatment for primary hypothyroidism in patients with pre-existing coronary artery disease or age >65?

A

Low-dose levothyroxine (25-50mg orally once daily, adjust dose in increments of 12.5 to 25mg every 4-6 weeks)

(Levothyroxine therapy may exacerbate angina in patients with CAD)

30
Q

What is the 1st line treatment for sub-clinical hypothyroidism with TSH>10mIU/L?

A

Low-dose levothyroxine (50-75mg/day, adjust dose in increments of 25-50mg to normalise TSH)

Repeat TFTs in 3-6 months

In patients >65/asymptomatic - observe and repeat TFTs in 6 months

31
Q

What should be checked regularly in hypothyroid patients receiving levothyroxine?

A

TSH should be checked annually - poor compliance = raised TSH and normal T4

32
Q

How is levothyroxine dose affected in pregnancy?

A

Should be increased up to 50% as early as 4-6 weeks into pregnancy

33
Q

What risk does overreplacement with thyroxine have?

A

Increased risk of osteoporosis (/ iatrogenic hyperthyroidism)

34
Q

How do we advise patients taking levothyroxine who also are taking iron/calcium supplements?

A

Take iron/calcium 4 hours apart from levothyroxine as they can reduce levothyroxine absorption

35
Q

What do we give patients with amiodarone-induced hypothyroidism?

A

Give levothyroxine and can continue amiodarone

36
Q

How do we treat myxoedema coma?

A
  • oxygen
  • rewarming
  • rehydration
  • IV T4 (levothyroxine) and T3 (liothyronine - faster onset of action)
  • IV hydrocortisone
  • treat underlying cause e.g. infection
37
Q

What are some complications of hypothyroidism?

A
  • myxoedema coma - older untreated patients with multiple comorbidities, mortality rate 80%
  • angina - high initial dose of levothyroxine in patients with CAD
  • over-treatment –> AF, osteoporosis
  • complications in pregnancy e.g. pre-eclampsia, perinatal mortality, recurrent miscarriage, foetal neurological maldevelopment
  • Hashimoto’s thyroiditis –> MALT lymphoma
38
Q

What is the prognosis for patients with hypothyroidism?

A
  • lifelong levothyroxine required
  • myxoedema coma has mortality rate of 80%

Year 3 (22 decks)

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