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Met3B > Hypothyroidism > Flashcards

Hypothyroidism Flashcards

1
Q

Define hypothyroidism

A

Clinical result of impaired production of the thyroid hormones, thyroxine (T4) and tri-iodothyronine (T3), which are essential for normal growth, development, and metabolism

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2
Q

The thyroid gland produces T3 and T4. Which is the more biologically active one?

A

T3

T4 is converted to the more biologically active T3 in peripheral tissues

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3
Q

How are thyroid hormones released?

A

Hypothalamus releases thyrotrophin-releasing hormone –> stimulates anterior pituitary to release TSH –> stimulates thyroid to release thyroid hormones

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4
Q

Define primary hypothyroidism

A

Thyroid gland is unable to produce thyroid hormones because of iodine deficiency or an abnormality within the gland itself.

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5
Q

Define secondary hypothyroidism

A

Insufficient production of bioactive TSH because of a pituitary or hypothalamic disorder

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6
Q

Define overt hypothyroidism

A

TSH levels are above the normal reference range (usually above 10 mU/L) and FT4 is below the normal reference range

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7
Q

Define subclinical hypothyroidism

A

TSH levels are above the normal reference range but T3 and T4 are within the normal reference range

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8
Q

Causes of primary hypothyroidism (8)

A

Iodine deficiency

Autoimmune thyroiditis (such as Hashimoto’s or atrophic thyroiditis)

Post-ablative therapy or surgery

Drugs - carbimazole, propylthiouracil, iodine, amiodarone, lithium, interferons, thalidomide, rifampicin

Subacute (de Quervain’s) thyroiditis

Postpartum thyroiditis

Thyroid infiltrative disorders
e.g. amyloidosis, sarcoidosis, haemochromatosis, tuberculosis, and scleroderma

Congenital hypothyroidism

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9
Q

Most common cause of hypothyroidism worldwide

A

Iodine deficiency

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10
Q

Most common cause of hypothyroidism in the UK

A

Autoimmunity (destruction of thyroid follicular cells by lymphocytes) e.g. Hashimoto’s

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11
Q

Causes of secondary hypothyroidism - pituitary (6)

A

Tumours — most commonly pituitary adenomas
Surgery, radiotherapy, or trauma
Infarction
Sheehan’s syndrome (postpartum pituitary necrosis due to postpartum haemorrhage)
Infiltrative disorders
Isolated TSH deficiency or inactivity

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12
Q

Causes of secondary hypothyroidism - hypothalamic (5)

A 
Tumours such as gliomas
Surgery, radiotherapy, or trauma
Infiltrative disorders
Idiopathic hypothalamic disease
Drugs (e.g. bexarotene and other retinoids)
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13
Q

Complications of hypothyroidism

A 
Impaired quality of life
Dyslipidaemia
Coronary heart disease and stroke
Heart failure
Impaired fertility
Pregnancy complications and adverse neonatal outcomes
Deafness, and impaired attention, concentration, memory, perceptual function, language, executive function, and psychomotor speed
Myxoedema coma
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14
Q

How does myxoedema coma present?

A

Hypothermia, coma, and seizures

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15
Q

Symptoms of primary hypothyroidism

A

Fatigue/lethargy.
Cold intolerance.
Weight gain.
Non-specific weakness, arthralgia, and myalgia.
Constipation.
Menstrual irregularities (menorrhagia)
Depression, impaired concentration, and memory.
Dry skin, and reduced body and scalp hair (such as sparse eyebrows).
Thyroid pain, for example in subacute (de Quervain’s) thyroiditis.

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16
Q

Signs of primary hypothyroidism

A

Coarse dry hair and skin
Hair loss
Oedema, including swelling of the eyelids
Hoarseness or deepening of the voice
Goitre
Bradycardia and diastolic hypertension
Delayed relaxation of deep tendon reflexes
Paraesthesia — due to carpal tunnel syndrome

17
Q

Symptoms and signs of secondary hypothyroidism

A

Those of primary hypothyroidism +/-
(headache, diplopia, or reduced peripheral vision) or (skin depigmentation, atrophic breasts, galactorrhoea, amenorrhoea, erectile dysfunction, loss of body hair, Cushing’s syndrome, or acromegaly)

18
Q

What to ask in history for hypothyroidism?

A

PC/HPC - weight gain, fatigue/lethargy, cold intolerance, constipation, menstrual irregularities, paraesthesia, memory loss, difficulty concentrating.

PMH - current or recent pregnancy, autoimmune disorders, Turner or Down’s syndrome, radioiodine treatment, surgery to head or neck, radiotherapy to head and neck, iodine deficiency, brain or metastatic cancer, infiltrative disease

DH - amiodarone, lithium

FH - thyroid or autoimmune disease

19
Q

What to look for in examination?

A

Weight gain, coarse facies, hair loss, lethargy, bradycardia, diastolic hypertension, and delayed relaxation of deep tendon reflexes.
Goitre and/or thyroid nodules.
Enlarged cervical lymph nodes.
Signs of carpal tunnel syndrome, autoimmune disease, myxoedema coma

20
Q

Bloods for hypothyroidism

A

TSH
FT4
Thyroid peroxidase antibodies (if TSH elevated)
Thyroglobulin antibodies (if TPOAb are negative)
FBC
HbA1c
Serum lipids

21
Q

Suspect secondary hypothyroidism if…?

A

Clinical features are suggestive
Low T4
Normal TSH (may be low)

22
Q

When may TFTs be misleading?

A

Pregnancy
Following treatment for hyperthyroidism
Following initiation of thyroxine
Poor compliance with treatment
Hypopituitarism
Following thyroiditis
Non-thyroidal illness (or sick euthyroid syndrome)
Drug treatment e.g. dopamine, glucocorticoids, propylthiouracil, amiodarone, and glucocorticoids
Several foods e.g. milk, coffee, soya products, and papaya.
End-organ resistance
Adrenal insufficiency
Obesity
Advancing age
Abnormal sleep patterns e.g. night shift workers

23
Q

Differentials for hypothyroidism

A 
Sick euthyroid syndrome
Diabetes mellitus
Adrenal insufficiency
Coeliac disease
Pernicious anaemia Hypopituitarism
Anaemia
Multiple myeloma
Chronic kidney disease
Chronic liver disease
Heart failure
Obesity
Hypercalcaemia
Electrolyte imbalance
Nutritional deficiencies - vitamin B1, folate, iron 
Anxiety and depression
Dementia
Chronic fatigue syndrome
Polymyalgia rheumatica
Fibromyalgia.
Obstructive sleep apnoea. 
Adverse effects of drugs such as beta-blockers, statins, and opiates.
Lifestyle — stressful life events, poor sleep pattern, work-related exhaustion, alcohol excess.
Viral and post-viral syndromes, or carbon monoxide poisoning.
24
Q

When to refer to endocrinology?

A

Suspected de Quervain’s thyroiditis
Goitre, nodule, or structural change in the thyroid gland
Suspected associated endocrine disease
Have adverse effects from levothyroxine (LT4) treatment
Female and planning pregnancy
Have pre-existing cardiac disease
Have atypical or misleading thyroid function tests
Are suspected of having an uncommon cause of hypothyroidism
Have a persistently raised TSH or symptoms despite adequate treatment

25
Q

Management of overt hypothyroidism

A

Levothyroxine (LT4)
Review the person every 3–4 weeks after initiation of LT4 and adjust the dose according to clinical and biochemical parameters
Once a stable TSH is achieved, TSH can be checked 4–6 monthly and then annually

26
Q

Management of subclinical hypothyroidism

A

If TSH is greater than 10mU/L, start LT4 (if <70 yo).

If TSH is between 4 and 10 mU/L and <65yo, consider trial of LT4 and assess response. If asymptomatic - watch and wait, repeat tests in 6 months.

27
Q

Hashimoto’s thyroiditis - what is it?

A

Autoimmune disease, associated with IDDM, Addison’s or pernicious anaemia
May cause transient thyrotoxicosis in the acute phase
5-10 times more common in women

28
Q

Starting dose of thyroxine for normal patients

Starting dose for those with cardiac disease, severe hypothyroidism or patients over 50

A

50-100mcg OD

25mcg OD

29
Q

Side effects of thyroxine

A

hyperthyroidism: due to over treatment
reduced bone mineral density
worsening of angina
atrial fibrillation

30
Q

After a dose change in thyroxine, when should TFTs be rechecked?

A

After 8-12 weeks

31
Q

In pregnancy, what should happen to thyroxine treatment?

A

Increase dose by at least 25-50 micrograms

32
Q

Blood results for poor compliance with thyroxine

A

High TSH, normal T4

33
Q

Blood results for sick euthyriod syndrome

A

Low TSH, low T4

34
Q

Features of Hashimoto’s

A

Features of hypothyroidism
Firm, non-tender goitre
Anti-thyroid peroxidase antibodies and also anti-Tg antibodies

Met3B (9 decks)

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