Hypothyroidism

Question 1

What does hypothyroidism result form

Answer 1

Insufficient secretion of thyroid hormones

Question 2

What are the 3 different forms of hypothyroidism

Answer 2

Primary
Subclinical
Central

Question 3

What is primary hypothyroidism characterised by

Answer 3

Low serum free thyroxine (T4) and high serum thyroid stimulating hormone (TSH) levels (due to a reduced negative feedback effect of T4 of TSH synthesis/ secretion)

Question 4

What is subclinical hypothyroidism defined as

Answer 4

Normal serum free T4 and T3 levels and a high serum TSH. This reflects the sensitivity of tTSH secretion to very small decreases in thyroid hormone secretion

Question 5

What is central hypothyroidism

Answer 5

Much less common
Results from reduced TSH secretion from the Anterior pituitary (secondary hypothyroidism) or reduced thyrotrophin-releasing hormone (TSH ) secretion from the hypothalamus (territory hypothyroidism)

Question 6

How common is hypothyroidism

Answer 6

1 in 4000 of the population

Question 7

What sex is hypothyroidism more common in

Answer 7

Females (5-8 times)

Question 8

What are some of the congenital causes of hypothyroidism

Answer 8

Thyroid agenesis

Dysgenesis or inherited defects in thyroid hormone biosynthesis

Question 9

What are some of the aquired causes of hypothyroidism

Answer 9

Chronic autoimmune (HASIMOTO’s) thyroiditis
Iatrogenic (drugs, thyroidectomy, radio iodine, neck radiotherapy)
Iodine deficiency / excess
Thyroiditis
Pituitary / hypothalamic damage (tumours, trauma, radiotherapy)

Question 10

What causes Hashimoto’s

Answer 10

Cellular and antibody-mediated injury to the thyroid tissue

Question 11

Patients with chronic autoimmune thyroiditis are more likely to have what ?

Answer 11

Personal or family history of other autoimmune conditions such as Assidosn’s disease and type 1 diabetes mellitus, vitiligo

Question 12

How can some patients become hypothyroid

Answer 12

Following radio iodine therapy for the treatment of Graves’ disease
After subtotal thyroidectomy for the treatment of Graves’ disease
External irradiation of the neck
Iodine deficiency and excess
In postpartum and subacute thyroiitis

Question 13

Describe the typical clinical presentation of hypothyroidism

Answer 13

Fatigue, lethargy, cold intolerance
Depression, goitre
Dry and course skin, pale / yellow tinge, oedematous
Course hair, hair loss, brittle nails
Bradycardia, exertional breathlessness, exacerbation of heart failure or angina
Hypercholestolaemia and hypertriglyceridaemia
Obstructive sleep apnoea
Constripaitonm, weight gain, ascites
Hyperprolactinaemia
Oligomenorrhoea/ ammenorrhoea, early abortion
Reduced libido, erectile dysfunction
Slowing of intellectual activities, movement, speech, impaired memory

Question 14

Describe the symptoms in secondary hypothyroidism compared to those in primary hypothyroidism

Answer 14

Symptoms are usually milder and may be masked by symptoms of other hormone deficiencies e.g. hot flushes secondary to hypogonadism

Question 15

What investigations should be carried out for suspected hypothyroidism

Answer 15

Measuring serum TSH and free T4
Hyperlipidaemia and hyponatraemia (in some patients)
Pituitary function tests and a MRI scan of the hypothalamus and pituitary for central hypothyroidism

Question 16

What is the treatment for hypothyroidism

Answer 16

Lifelong treatment with synthetic levothyroxine

Question 17

What are the objectives of treatment

Answer 17

Resolution of symptoms, a normalisation of TSH and a reduction in the size of the goitre in patients with Hashimoto’s thyroiditis

Question 18

What is the dose of levothyroxine for younger patients (under 50)

Answer 18

50ug daily

Dose is increased by 25g until the TSH is in the normal range and as close to 1.0mU/L as possible

Question 19

What is the average dose of levothyroxin in hypothyroid adults

Answer 19

100ug per day but the range varies from 50-200

Question 20

How should levothyroxine be taken

Answer 20

On an empty stomach

Question 21

What is the treatment for myxoedema coma

Answer 21

Intensive care unit Mechanical ventilation for respiratory failure
Bloods for culture, free T4, T3, TSH and cortisol before starting treatment
IV levothyroxine 300-500ug
IV hydrocortisone
Replace IV fluids and glucose appropriately
Correct hypoterhmia using a heating blanket

Question 22

What is myxoedema coma

Answer 22

Myxedema coma is a state of decompensated hypothyroidism. A person may have lab values identical to a “normal” hypothyroid state, but a stressful event (such as an infection, myocardial infarction or stroke) precipitates the myxedema coma state, usually in the elderly.

Question 23

If adrenal insufficiency or secondary hypothyroidism is suspected, what should be done prior to commencing treatment ?
why?

Answer 23

Short Synacthen test

it can cause Addisonian crisis in patients with untreated adrenal insufficiency

Question 24

When should TSH be measured after starting oestrogen therapy

Answer 24

12 weeks

Question 25

What is the dose of levothyroxine in older patients (over 50)

Answer 25

Older patients should start on just 25g daily as they may have ischaemic heart disease and levothyroxine increases myocardial oxygen demand