Hypothyroidism Flashcards

1
Q

What is hypothyroidism?

A

Hypothyroidism is a common endocrine condition caused by a deficiency in thyroid hormone.

Reduction in circulating T3 and T4

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2
Q

What are the classification for hypothyroidism?

A

Primary - 95% of cases
Secondary
Congenital

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3
Q

Epidemiology

A
  • Hypothyroidism 1-2% in world
  • Hashimoto’s thyroiditis being the most common cause in the developed world. Iodine deficiency is the most common cause worldwide.
  • Female gender: 5-8x more likely to develop than men
  • Middle-aged: peak age is 30-50 years old in Hashimoto’s thyroiditis
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4
Q

Hashimotos thyroiditis

A
  • Autoimmune process associated withHLA-DR5andanti-TPO antibodies,which act as competitive inhibitors for the enzyme
  • Associated with other autoimmune conditions e.g. type 1 diabetes and Addisons disease
  • Diffuse painless goitre and can experience a transient thyrotoxic state known as hashitoxicosis
  • 5-10x more common in women
  • Increased risk of Non-Hodgkin lymphoma
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5
Q

De Quervain’s thyroiditis

A
  • Follows a viral prodrome and can also present with a transient thyrotoxic state
  • Painfulgoitre withraised inflammatory markers. Usually self-limiting
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6
Q

Post partum thyroiditis

A
  • Autoimmune with most patients developingthyrotoxicosiswithin the first 6 months of birth, with subsequenthypothyroidism
  • Most patients’ thyroid function normalises by 12 months
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7
Q

Riedels thyroiditis

A
  • Hard non-tender thyroid goitre due to fibrous tissue
  • Causes a painless goitre
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8
Q

Iodine deficiency

A
  • Commonest causeworldwide, due to dietary deficiency
  • Uncommon in the developed world due to iodine-fortified salt and foods
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9
Q

Post- thyroidectomy or post radioiodine

A

After treatment for hyperthyroidism e.g. Graves’ disease, patients can experience long term hypothyroidism and require levothyroxine replacement

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10
Q

Drugs that cause primary hypothyroidism

A
  • Amiodarone - can cause both hyperthyroidism (due to the high iodine content of amiodarone) and hypothyroidism (since it also inhibits the conversion of T4 to T3)
  • Lithium
  • Anti-thyroid drugs e.g. carbimazole
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11
Q

Secondary causes of hypothyroidism

A
  • Often due to compression from apituitarytumour(e.g. adenoma), but may occur following surgery/radiation or vascular pathology (e.g. pituitary apoplexy)
  • Rarely, it may be due tohypothalamicpathology, e.g. a tumour
  • Drugs: cocaine, steroids and dopamine all inhibit TSH secretion
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12
Q

What is primary hypothyroidism?

A

due to pathology affecting the thyroid gland itself, such as an autoimmune disorder (e.g. Hashimoto’s thyroiditis) or iodine deficiency.

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13
Q

What is Secondary hypothyroidism?

A

usually due to pathology affecting thepituitarygland (e.g. pituitary apoplexy) or a tumour compressing the pituitary gland. It may also be caused byhypothalamicdisorders and certain drugs.

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14
Q

What is congenital hypothyroidism?

A

occurs due to an absent or poorly developed thyroid gland (dysgenesis), or one that has properly developed but cannot produce thyroid hormone (dyshormonogenesis).

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15
Q

RFs for hypothyroidism

A
  • Family history
  • History of autoimmunity
  • Genetic disorders: Turner and Down syndrome
  • Chest or neck irradiation
  • Thyroidectomy or radioiodine
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16
Q

Signs of hypothyroidism

A
  • Dermatological: hair loss, loss of lateral aspect of the eyebrows (Queen Anne’s sign), dry and cold skin, coarse hair
  • Bradycardia
  • Goitre
  • Decreased deep tendon reflexes
  • Carpal tunnel syndrome
  • Hoarse voice
17
Q

Symptoms of hypothyroidism

A

Weight gain
Fluid retention
Dry skin
Constipation
Lethargy

18
Q

First line investigations for hypothyroidism

A

TFTs:
Hashimoto’s (primary hypothyroidism) TSH High T3/T4 Low
Subclinical hypothyroidism High TSH Normal T4
Secondary hypothyroidism Low/ normal TSH Low T4

19
Q

Other investigations to do for hypothyroidism

A

Antibodies:Anti-TPO is associated with Hashimoto’s thyroiditis in 95% of cases
Inflammatory markers:raised in de Quervain’s thyroiditis

20
Q

Can also do for hypothyroidism investigations

A

US
Fasting lipids
Serum glucose + HbA1c
FBC

21
Q

1st line therapy for hypothyroidism

A

Levothyroxine (T4):offer with regular review of symptoms and TSH every 3 months. Once TSH is stable (on 2 occasions at least 6 months apart), review TSH annually

Aim to maintain serum TSH and T4 levels at normal range

22
Q

What must all patients with secondary hypothyroidism require?

A

urgent referral to an endocrinologist.

23
Q

Pregnancy and postpartum hypothyroidism

A
  • If TFTs are abnormal, advise delaying conception and using contraception until stabilised on levothyroxine
  • Inform the woman that there is anincreased demand for levothyroxinein pregnancy, with the dose usually increased by at least 25-50 mcg and aiming for a low-normal TSH
24
Q

Complications of hypothyroidism

A

CVD - hypercholesterolaemia is associated with ischaemic heart disease
Neuro - Carpal tunnel, peripheral neuropathy
Myxoedema coma
Thyroid lymphoma

25
Q

Thyroxine side effects

A
  • Hyperthyroidism
  • Atrial fibrillation
  • Osteoporosis
  • Angina
26
Q

What is Hashimotos Thyroiditis?

A

The most common cause of hypothyroidism in the West. Antithyroid antibodies is the cause for this type of hypothyroidism

27
Q

Epidemiology of Hashimotos Thyroiditis

A
  • It is estimated to affect between 0.5% and 2% of the population.
  • More common in FEMALES than males
  • Incidence increases with age
28
Q

RFs for Hashimotos Thyroiditis

A
  • Female sex
  • Associated with other autoimmune disease e.g. T1DM
  • Associations with Turner’s and Down’s syndrome