Hypothyroidism

Question 1

What is hypothyroidism?

Answer 1

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

Reduction in circulating T3 and T4

Question 2

What are the classification for hypothyroidism?

Answer 2

Primary - 95% of cases
Secondary
Congenital

Question 3

Epidemiology

Answer 3

• 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

Question 4

Hashimotos thyroiditis

Answer 4

• 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

Question 5

De Quervain’s thyroiditis

Answer 5

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

Question 6

Post partum thyroiditis

Answer 6

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

Question 7

Riedels thyroiditis

Answer 7

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

Question 8

Iodine deficiency

Answer 8

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

Question 9

Post- thyroidectomy or post radioiodine

Answer 9

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

Question 10

Drugs that cause primary hypothyroidism

Answer 10

• 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

Question 11

Secondary causes of hypothyroidism

Answer 11

• 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

Question 12

What is primary hypothyroidism?

Answer 12

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

Question 13

What is Secondary hypothyroidism?

Answer 13

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.

Question 14

What is congenital hypothyroidism?

Answer 14

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

Question 15

RFs for hypothyroidism

Answer 15

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

Question 16

Signs of hypothyroidism

Answer 16

• 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

Question 17

Symptoms of hypothyroidism

Answer 17

Weight gain
Fluid retention
Dry skin
Constipation
Lethargy

Question 18

First line investigations for hypothyroidism

Answer 18

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

Question 19

Other investigations to do for hypothyroidism

Answer 19

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

Question 20

Can also do for hypothyroidism investigations

Answer 20

US
Fasting lipids
Serum glucose + HbA1c
FBC

Question 21

1st line therapy for hypothyroidism

Answer 21

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

Question 22

What must all patients with secondary hypothyroidism require?

Answer 22

urgent referral to an endocrinologist.

Question 23

Pregnancy and postpartum hypothyroidism

Answer 23

• 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

Question 24

Complications of hypothyroidism

Answer 24

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

Question 25

Thyroxine side effects

Answer 25

- Hyperthyroidism - Atrial fibrillation - Osteoporosis - Angina

Question 26

What is Hashimotos Thyroiditis?

Answer 26

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

Question 27

Epidemiology of Hashimotos Thyroiditis

Answer 27

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

Question 28

RFs for Hashimotos Thyroiditis

Answer 28

- Female sex - Associated with other autoimmune disease e.g. T1DM - Associations with Turner's and Down's syndrome