Hypothyroidism

Question 1

Epidemiology of hypothyroidism in the UK

Answer 1

1-2%

Question 2

What is hypothyroidism?

Answer 2

A clinical state resulting from underproduction of the thyroid hormones T3 and T4

Question 3

Primary vs secondary hypothyroidism

Answer 3

93% of cases are primary meaning the thyroid gland fails to produce the hormones

7% are secondary - the pituitary fails to produce enough thyroid stimulating hormone

Question 4

Findings from thyroid function tests for primary and secondary hypothyroidism

Answer 4

Primary: T3 low, T4 low, TSH high

Secondary: T3 low, T4 low, TSH low

Question 5

Why is myxoedema coma?

Answer 5

Rare severe form of hypothyroidisn with mutli organ failure

A state of decompensated hypothyroidism

Altered mental status

Low body temperature

Low blood sugar

Low BP

Hyponatremia

Hypercapnia

Hypoxia

Bradycardia

Hypoventilation

Mucinous substance deposited in the skin which causes thickening

Question 6

Why does myxoedema coma occur?

Answer 6

Thyroid hormones are needed for cellular metabolism so without it this doesn’t occur. They also stimulates cellular oxygen consumption

heart: impaired contractility
brain: reduced oxygen delivery and confusion
lungs: hypoventilation

essentially everything slow down to a point where death can occur - 25-60% mortality

Question 7

Management of myxoedema coma

Answer 7

Airway management

IV thyroid hormone replacement is needed as gastrointestinal absorption is reduced

Patients show imporvement generally within a week

Question 8

What is a major cause of hypothyroidism in developing countries?

Answer 8

Iodine deficiency

Question 9

What supplies blood to the thyroid gland?

Answer 9

Superior and inferior thyroid artery

Question 10

Synthesis of thyroid hormones

Answer 10

ER within thyroid follicular cells synthesises thyroglobulin

Thyroglobulin is then packaged and sent to the colloid of the thyroid gland

Sodium and iodide are transpprted from the blood into the thyroid follicular cells

Iodide is then transported into the colloid where iodide is transformed to iodine

Iodine then binds to the thyroglobulin and this forms the thyroid hormones (whether it is T3 or T4 depends on the amount of iodine molecules linked to the thyroglobulin)

Question 11

What is the most common cause of hypothyroidism?

Answer 11

Hashimoto’s autoimmune thyroiditis

Affects women 9x more than men

Peak incidence age 30-50

Question 12

Causes of hypothyroidism other than Hashimoto’s

Answer 12

Removal of thyroid gland

Radioiodine therapy for Grave’s

Head and neck cancer xRT

Lymphocytic thyroiditis - affects 6% of post partum women and causes transient hypothyroidism

Question 13

Pathophysiology of autoimmune thyroiditis

Answer 13

When you have Hashimoto’s thyroiditis, your immune cells mistakenly attack your healthy thyroid tissue

Thyroid infiltrated with lymphocytes

95% of patients have antithyroid peroxidase antibodies

60% have antithyroglobulin antibodies

Thyroid can become so inflamed it causes a goitre to form but this is relatively uncommon

Question 14

Which drugs are known to cause hypothyroidism?

Answer 14

Amiodarone: interferes with thyroid hormone synthesis and reducing the conversion of T4 to T3

Lithium: interferes with thyroid hormone secretion

Question 15

Symptoms of hypothyroidism

Answer 15

Think everything has slowed down

Weakness

Lethargy

Fatigue

Hoarseness

Feeling cold

Forgetfulness

Constipation

Weight gain

Slow speech and movement

Dry skin

Eyelid oedema

Thich tongue

Bradycardia

Diastolic hypertension

Delayed reflexes

Question 16

Primary investigation for hypothyroidism

Answer 16

Serum TSH

Hypothyroidism - TSH elevated

Question 17

Other investigations to consider for hypothyroidism

Answer 17

Free serum T3: normal range is 9.00-23.12 picomol/L (0.8-1.8 nanograms/dL). Low free T4 with elevated TSH is diagnostic of primary hypothyroidism. Low T4 and low TSH indicates central or secondary hypothyroidism

FBC: a mild, normocytic anaemia sometimes occurs

Fasting blood glucose: primary hypothyroidism is associated with type 1 diabetes so blood glucose may be elevated

Antithyroid peroxidase antibodies: elevated in over 90% of patients with Hashimoto’s, if hypothyroidism the levels will be elevated

Question 18

How is hypothyroidism managed?

Answer 18

Levothyroxine

Lower doses for those with coronary artery disease because it is known to exacerbate the condition

Question 19

Most common cause of autoimmune thyroiditis in developed countries

Answer 19

Excessive iodine

Question 20

Levothyroxine requirements during pregnancy

Answer 20

Requirements increase so dose may need adjusting

Question 21

What is central hypothyroidism?

Answer 21

Due to anterior pituitary or hypothalamic dysfunction

Characterised by a decrease in TSH which in turn causes a decrease in thyroid hormone synthesis

Rare <1% of cases

Pituitary adenomas are the most common cause

Question 22

What is De Quervain’s thyroiditis?

Answer 22

Painful swelling of the thyroid gland

Usually due to viral infections e.g. mumps or flue

Usually causes a short hyperthyroid period followed by hypothyroidism which can last for weeks - months

Self limiting and not usually treated but if hyperthyroid symtoms are treated a beta blocker is used