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Endocrinology - Rachel Doohan Y5 > Hypothyroidism > Flashcards

Hypothyroidism Flashcards

1
Q

Provide a definition of hypothyroidism

A

Hypothyroidism is the insufficient production/ secretion of thyroid hormones which can be due a variety of causes.

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2
Q

What does myxoedema mean

A

Myxoedema is a term used synonymously with severe hypothyroidism and is a medical emergency.

(Myxoedema should NOT be confused with pre-tibial myxoedema which is a dermatological sign which can be seen in grave’s disease).

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3
Q

What does primary hypothyroidism mean

A

Primary hypothyroidism is the insufficient production of thyroid hormones due to a problem within the thyroid gland itself.

Clinical Investigations will show:

> Low T3 and T4

> High TSH:

Because there is no issue with the feedback loop and the anterior pituitary gland is able to detect the low levels of circulating thyroid hormones and exhibit a normal physiological response by increasing its production and secretion of TSH (thyroid stimulating hormone) to try and stimulate the thyroid gland to produce more thyroid hormone to normalise thyroid hormone levels (which obviously wont work as the thyroid gland is unable to respond to the rising levels of TSH).

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4
Q

What does secondary hypothyroidism mean

A

Secondary hypothyroidism is the insufficient production of thyroid hormones due to a problem with the production/ secretion of TSH (thyroid stimulating hormone) from the anterior pituitary gland.

i.e. the problem is within the pituitary gland rather than being with the thyroid gland.

Clinical Investigations will show:

> Low T3 and T4 because the thyroid gland is not being adequately stimulated by TSH to produce normal levels of thyroid hormone

> Low TSH because the root cause of the hypothyroidism is the inadequate production/ secretion of TSH from the anterior pituitary gland.

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5
Q

What does tertiary hypothyroidism mean?

A

Tertiary hypothyroidism is the insufficient production of thyroid hormones due to a problem with the production/ secretion of TRH (Thyrotropin releasing hormone) from the hypothalamus.

i.e. the problem is within the hypothtalamus rather than being in the pituitary gland or the thyroid gland ow thyroid hormones caused by reduced release of TRH from the hypothalamus (low T3 and T4, low TSH)

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6
Q

epidemiology of hypothyroidism

A

increased incidence in white populations and in places where they have a high iodine intake

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7
Q

causes of primary hypothyroidism subtypes

A
  • goitrous causes
  • non-goitrous causes
  • self-limiting causes
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8
Q

goitrous causes of primary hypothyroidism

A
  • chronic thyroiditis (hashimos thyroiditis)
  • iodine deficiency (number 1 cause of primary hypothyroidism worldwide but less common in the west)
  • drug induced (lithium and amiodarone)
  • maternally transmitted if mother is receiving treatment for hyperthyroidism
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9
Q

non-goitrous causes of primary hypothyroidism

A
  • atrophic thyroiditis
  • post-ablative therapy for hyperthyroidism (radio iodine)
  • thyroidectomy
  • post radiotherapy (i.e. for treatment of lymphoma of the neck)
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10
Q

self-limiting causes of primary hypothyroidism

A
  • withdrawal of anti-thyroid medication
  • post partum thyroiditis (usually begins as hyperthyroidism and progresses to hypothyroidism)
  • subacute thyroiditis with transient hypothyroidism
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11
Q

hair and skin symptoms in hypothyroidism

A 
coarse dry hair
dry pale skin 
periorbital puffiness
hypercarotenaemia 
cold intolerance 
fluid retention causing pitting oedema 
vitiligo may be present
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12
Q

cardiac symtoms in hypothyroidism

A 
bradycardia
cardiac dilatation
pericardial effusion
worsening of heart failure 
hyperlipidaemia can cause xathelasma
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13
Q

GI symtoms in hypothyroidism

A 
weight gain despite reduced appetite 
constipation 
intestinal obstruction (rare)
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14
Q

respiratory symptoms in hypothyroidism

A

obstructive sleep apnoea
deep hoarse voice (rare)
macroglossia (rare)

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15
Q

neurological/ CNS symptoms of hypothyroidism

A 
depression
 muscle stiffness and cramps
 carpal tunnel syndrome
slow movements and thoughts
loss of libido
hyporeflexia with delayed relaxation
decreased visual acuity
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16
Q

gynae/ reproductive symtoms

A

menorrhagica (heavy periods)

hyperprolactinaemia (elevation of serum prolactin because increased TRH secretion causes increased PRL secretion)

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17
Q

laboratory investigations for primary hypothyroidism

A
  • high TSH low fT3 and fT4
  • macrocytosis (increased red blood cell size)
  • increased creatinine kinase
  • increased LDL cholesterol
  • hyponatraemia
  • hyperprolactinaemia
18
Q

management of hypothyroidism general rule

A

normal metabolic rate should be restored gradually, if restored to quickly there is a risk of cardiac arrhythmias occurring

19
Q

management of hypothyroidism in younger patients

A

50-100micrograms of levothyroxine daily

20
Q

management of hypothyroidism in elderly patients with ischaemic heart disease

A

start with levothyroxine 25-50 micrograms daily and adjust every month according to response (i.e. titrate dose up slowly)

21
Q

once stabilised check

A

TSH levels every 12 months, in those with secondary hypothyroidism TSH levels are not reliable as they are low so use fT4 level to titrate dose

22
Q

levothyroxine

A

T4

  • take before breakfast
  • do not take at the same time as calcium, iron or proton pump inhibitors as they reduce its absorption
23
Q

during pregnancy dose of levothyroxine

A

should be increased by about 25-50% because there is an increase in thyroxine binding protein during pregnancy

24
Q

myxoedema coma

A

decompensated severe hypothyroidism most commonly precipitated by a stressful event in the elderly (myocardial infarction, infection stroke)

25
Q

people with myxoedema coma don’t necessarily

A

have to be in a coma but it can progress to a coma if untreated

26
Q

ECG in myxoedema coma

A

bradycardia, low voltage complexes, varying degrees of heart block, T wave inversion, prolongation of QT interval

27
Q

what else can occur in myxoedema coma

A

type 2 respiratory failure: hypoxia, hypercarbia, respiratory acidosis

28
Q

what do 10% of people who have myxoedema also have

A

co-existing adrenal failure

29
Q

management of myxoedema coma should be in

A

ICU

30
Q

management

A
  • IV thyroxine (but use carefully as if someone has adrenal failure then they should never be given thyroxine unless they have been given steroids a few hours prior)
  • IV hydrocortisone until you have ruled out adrenal failure
  • passively rewarm with 0.3% sodium chloride
  • cardiac monitoring, central venous pressure, blood sugars
  • may require intubation
31
Q

chronic thyroiditis also known as

A

hashimotos thyroiditis

32
Q

hashimotos thyroiditis

A

hypothyroidism caused by autoimmune destruction of the thyroid glands

33
Q

hashimotos thyroiditis is the

A

number once cause of hypothyroidism in the west

34
Q

who is hashimotos thyroiditis more common in

A

10-15x more common in woman and average age of onset is 30-40 years old

35
Q

hashimotos thyroiditis is associated with

A

other autoimmune conditions such as:

  • vitiligo
  • systemic lupus erythematosus
  • rheumatoid arthritis
  • primary biliary cirrhosis
  • addisons disease
36
Q

antibodies in hashimotos

A
  • anti-TPO (antibodies against thyroid peroxidase)

- anti-Tg (antibodies against thyroglobulin)

37
Q

whats the best diagnostic test for hashmiotos

A

thyroid biopsy which shows T cell infiltrate and inflammation

38
Q

who can hashimotos not occur in

A

children

39
Q

what can hashimotos rarely present with

A

hashitoxicosis which is hyperthyroidism in the intimal stages of the disease caused by the release of thyroid hormones while the thyroid gland is being destroyed

40
Q

why does hypercarotonaemia occur

A

because of impaired conversion of beta carotene to vitamin A

41
Q

loss of the other third of the eyebrow is called

A

sign of hertoghe

Endocrinology - Rachel Doohan Y5 (28 decks)

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