Hypothyroidism Flashcards
Define hypothyroidism
Clinical result of impaired production of the thyroid hormones, thyroxine (T4) and tri-iodothyronine (T3), which are essential for normal growth, development, and metabolism
The thyroid gland produces T3 and T4. Which is the more biologically active one?
T3
T4 is converted to the more biologically active T3 in peripheral tissues
How are thyroid hormones released?
Hypothalamus releases thyrotrophin-releasing hormone –> stimulates anterior pituitary to release TSH –> stimulates thyroid to release thyroid hormones
Define primary hypothyroidism
Thyroid gland is unable to produce thyroid hormones because of iodine deficiency or an abnormality within the gland itself.
Define secondary hypothyroidism
Insufficient production of bioactive TSH because of a pituitary or hypothalamic disorder
Define overt hypothyroidism
TSH levels are above the normal reference range (usually above 10 mU/L) and FT4 is below the normal reference range
Define subclinical hypothyroidism
TSH levels are above the normal reference range but T3 and T4 are within the normal reference range
Causes of primary hypothyroidism (8)
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
Most common cause of hypothyroidism worldwide
Iodine deficiency
Most common cause of hypothyroidism in the UK
Autoimmunity (destruction of thyroid follicular cells by lymphocytes) e.g. Hashimoto’s
Causes of secondary hypothyroidism - pituitary (6)
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
Causes of secondary hypothyroidism - hypothalamic (5)
Tumours such as gliomas Surgery, radiotherapy, or trauma Infiltrative disorders Idiopathic hypothalamic disease Drugs (e.g. bexarotene and other retinoids)
Complications of hypothyroidism
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
How does myxoedema coma present?
Hypothermia, coma, and seizures
Symptoms of primary hypothyroidism
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.
Signs of primary hypothyroidism
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
Symptoms and signs of secondary hypothyroidism
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)
What to ask in history for hypothyroidism?
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
What to look for in examination?
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
Bloods for hypothyroidism
TSH
FT4
Thyroid peroxidase antibodies (if TSH elevated)
Thyroglobulin antibodies (if TPOAb are negative)
FBC
HbA1c
Serum lipids
Suspect secondary hypothyroidism if…?
Clinical features are suggestive
Low T4
Normal TSH (may be low)
When may TFTs be misleading?
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
Differentials for hypothyroidism
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.
When to refer to endocrinology?
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
