Hypothyroidism Flashcards
What is hypothyroidism?
It is is defined as a condition in which there is inadequate output of thyroid hormones by the thyroid gland
What are the two classifications of hypothyroidism?
Primary Hypothyroidism
Secondary Hypothyroidism
What is primary hypothyroidism?
It is defined as hypothyroidism resulting from a dysfunction within the thyroid gland
What are the six causes of primary hypothyroidism?
Hashimoto’s Thyroiditis
Riedel Thyroiditis
De Quervain’s Thyroiditis
Iodine Deficiency
Drug Administration
Thyroidectomy
What is the most common cause of primary hypothyroidism in the developed world?
Hashimoto’s thyroititis
What is Hashimoto’s thyroiditis?
It is defined as autoimmune inflammation of the thyroid gland due to the production of antithyroid peroxidase (anti-TPO) and antithyroglobulin (anti-Tg) antibodies against thyroid epithelial cells
What does Hashimoto’s thyroiditis cause acutely?
Transient hyperthyroidism
What are the three other autoimmune conditions Hashimoto’s thyroiditis is associated with?
Coeliac Disease
Type One Diabetes Mellitus
Vitiligo
What complication is associated with Hashimoto’s thyroiditis?
MALT lymphoma
What is Riedel thyroiditis?
It is a condition in which fibrous tissue replaces normal thyroid parenchyma
This results in the formation of painless goitre
What is another term for De Quervain’s thyroiditis?
Subacute thyroiditis
What is De Quervain’s thyroiditis?
It is a painful swelling of the thyroid gland thought to be triggered by a viral infection
How many phases of De Quervain’s thyroiditis are there?
Four
What is the first phase of De Quervain’s thyroiditis? How long does it last for?
It results in hyperthyroidism, painful goitre and raised ESR
3 - 6 weeks
What is the second phase of De Quervain’s thyroiditis? How long does it last for?
Euthyroid
1 -3 weeks
What is the third phase of De Quervain’s thyroiditis? How long does it last for?
Hypothyroidism
Weeks to months
What is the fourth phase of De Quervain’s thyroiditis?
It results in a normal thyroid structure and function
How do we manage hypothyroidism related to De Quervain’s thyroiditis?
It is a self-limiting condition, which can be managed with NSAIDs for symptomatic relief
How do we manage severe De Quervain’s thyroiditis?
Corticosteroids
What is the most common cause of primary hypothyroidism in the developing world?
Iodine deficiency
What are the two causes of iodine deficiency?
Decreased dietary consumption
Radioiodine treatment
What are the three drugs which are associated with hypothyroidism?
Anti-thyroid drugs
Lithium
Amiodarone
Name two anti-thyroid drugs
Carbimazole
Propylthiouracil
How does lithium cause hypothyroidism?
It inhibits the production of thyroid hormones in the thyroid gland
How does amiodarone cause hypothyroidism?
It is due to the high iodine content of amiodarone causing a Wolff-Chaikoff effect.
This an autoregulatory phenomenon where thyroxine formation is inhibited due to high levels of circulating iodide
What is the management option of amiodarone induced hypothyroidism?
We administer levothyroxine and continue amiodarone
What is secondary hypothyroidism?
It is defined as hypothyroidism resulting from a dysfunction within the pituitary gland – a gland which regulates the thyroid gland
Specifically, the pituitary gland is unable to produce enough TSH
What are the six causes of secondary hypothyroidism?
Sheehan’s Syndrome
Pituitary Adenoma
Craniopharyngioma
Coeliac Disease
Down’s Syndrome
Turner’s Syndrome
What is Sheehan’s syndrome?
It is a condition in which there is life-threatening blood loss during childbirth – resulting in ischaemic necrosis of the pituitary gland
What is the most common cause of hypothyroidism in children?
Autoimmune Thyroiditis
What are the eleven clinical features of hypothyroidism?
Weight Gain
Fatigue
Cold Intolerance
Anhidrosis, Yellow Skin
Non-Pitting Oedema
Dry Coarse Scalp Hair
Voice Hoarseness
Decreased Deep Tendon Reflexes
Carpal Tunnel Syndrome
Constipation
Menorrhagia
What investigation is used to diagnose hypothyroidism?
Blood tests
What three blood results indicate primary hypothyroidism?
Decreased T3 Levels
Decreased T4 Levels
Increased TSH Levels
Explain the blood test results of primary hypothyroidism
It is caused by thyroid gland dysfunction, therefore free T3 and T4 levels will be low
The TSH levels will be high due to the fact that there is no negative feedback inhibition on the pituitary to release these hormones
What two additional blood results indicate primary hypothyroidism - related to Hashimoto’s disease?
Anti-TPO Positive
Anti-Tg Positive
What three blood results indicate secondary hypothyroidism?
Decreased T3 Levels
Decreased T4 Levels
Decreased TSH Levels
Explain the blood test results of secondary hypothyroidism
It is caused by pituitary gland dysfunction, therefore TSH levels will be low
The resulting effect is that free T3 and T4 levels will also be low
How do we manage hypothyroidism?
Levothyroxine
What is levothyroxine?
It is synthetic T4 hormone
What dose of levothyroxine do we administer in adults < 50 years old?
It is initiated on a dose of 50 – 100mcg once daily, with this dose slowly titrated until TSH levels are normalised
What dose of levothyroxine do we administer in adults > 50 years old OR cardiac disease OR severe hypothyroidism?
It is initiated on a dose of 25mcg once daily, with this dose slowly titrated until TSH levels are normalised
What is the single most important blood test used to assess response to levothyroxine?
TSH Levels
How often do we conduct TFT blood tests when individuals are administrated levothyroxine?
They are measured every three months until TSH levels are stable, with two similar measurements within the reference range three months apart
After this TSH levels can then be measured once a year
How often do we conduct TFT blood tests when individuals are administrated levothyroxine - and a change in dose occurs?
They are conducted every 8 -12 weeks
What are the four side effects of levothyroxine?
Hyperthyroidism
Osteoporosis
Angina
Atrial fibrillation
What two drugs does levothyroxine interact with? What does this result in? How do we prevent this?
Iron
Calcium carbonate
Decreased absorption of levothyroxine
We administer these drugs four hour apart
What two blood test results indicate poor compliance of levothyroxine? Explain
Increased TSH levels
Normal T4 Levels
The increased TSH levels implies that over recent days/weeks her body is thyroxine deficient
However, her free T4 is within normal range. This indicates that she started taking the thyroxine properly just before the blood test
This would correct the thyroxine level but the TSH takes longer to normalise
How do we adjust the levothyroxine dose when hypothyroid individuals become pregnant? Why?
The dose should be increased by at least 25 – 50 mcg as early as 4 -6 weeks of pregnancy
This is due to the increased demands of pregnancy
How often do we conduct blood tests in hypothyroid pregnant patients?
4 times weekly, until they are 20 weeks
How do we adjust the levothyroxine dose once hypothyroid individuals have given birth?
We reduce their levothyroxine dosage to the pre-pregnancy dose two weeks following delivery
We then recheck that their levels are stable two to three months post pregnancy
What is a complication of hypothyroidism?
Myxoedema Coma
What is myxoedema coma?
It is defined as a is a rare life-threatening complication of hypothyroidism
What are the eight clinical features of myxoedema comas?
Hypothermia
Bradycardia
Hyporeflexia
Seizures
Thin, Brittle Hair
Perioribtal Oedema
Confusion
Coma
What are the four management options of myxoedema coma?
IV Thyroid Replacement
IV Fluids
IV Corticosteroids
Electrolyte Imbalance Correction
What is subclinical hypothyroidism?
It is defined as a condition in which TSH levels are elevated, however the free serum thyroxine and triiodothyronine levels are normal
What is the pathophysiological cause of subclinical hypothyroidism?
The thyroxine hormone levels are at the lower range of normal, resulting in an increased secretion of TSH to suppress this
How do we manage subclinical hypothyroidism in individuals with a TSH > 10?
We consider administration of levothyroxine
How do we manage subclinical hypothyroidism in symptomatic individuals with a TSH between 5.5 - 10?
We consider a trial of levothyroxine for a period of six months
How do we manage subclinical hypothyroidism in asymptomatic individuals with a TSH between 5.5 - 10?
We observe and repeat thyroid function in six months
What are the four clinical features of congenital hypothyroidism?
Hypotonia
Macroglossia
Puffy face
Neonatal jaundice
