Hypothyroidism (E&M) Flashcards
Define hypothyroidism.
Clinical state resulting from underproduction of the thyroid hormones thyroxine (T4) and triiodothyronine (T3)
What are some different types of hypothyroidism?
- primary
- secondary
- sub-clinical
- myxoedema coma
Define primary hypothyroidism.
- most cases are due to primary hypothyroidism
- failure of the thyroid gland to produce thyroid hormone
- TSH concentrations above the reference range and free thyroxine concentrations below the reference range
Define secondary hypothyroidism.
Underproduction of TSH by the pituitary gland
Define sub-clinical hypothyroidism.
State of usually asymptomatic, mild thyroid failure, with normal levels of T4 and T3, and minimal elevation of TSH (may occur in intercurrent illness)
(Sub-clinical = not detected by usual clinical tests)
Define myxoedema coma.
Rare severe form of hypothyroidism with multi-organ failure
What are some congenital causes of hypothyroidism?
- thyroid dysgenesis
- inherited defects in thyroid hormone biosynthesis
- thyroid dysplasia / aplasia
What are some acquired causes of hypothyroidism?
- Hashimoto’s thyroiditis (autoimmune): goitre due to lymphocytic and plasma cell infiltration
- primary atrophic hypothyroidism: diffuse lymphocytic infiltration of the thyroid –> atrophy, no goitre
- iatrogenic: post-thyroidectomy, radioiodine, hyperthyroid medication, amiodarone, lithium, iodine
- severe iodine deficiency (chief cause worldwide)
- iodine excess (Wolff-Chaikoff effect)
- thyroiditis: subacute temporary hypothyroidism after hyperthyroid phase (post-partum thyroiditis / de Quervain thyroiditis)
What causes secondary hypothyroidism?
Pituitary disorders e.g. pituitary adenoma –> TSH deficiency
What group does hypothyroidism occur more commonly in?
F > M
What is the most common cause of hypothyroidism worldwide?
- iodine deficiency
- in developed countries where this is not an issue, Hashimoto’s thyroiditis
What more serious condition is Hashimoto’s thyroiditis linked with?
MALT lymphoma
What are some risk factors for hypothyroidism?
- iodine deficiency
- female sex
- middle age
- Fx of autoimmune thyroiditis
- autoimmune disorders
- treatment for thyroid disease
- post-partum thyroiditis
- Turner’s and Down’s syndromes
- radiotherapy to head and neck
- amiodarone/lithium use
What are some non-specific symptoms of hypothyroidism? (4)
- weakness
- lethargy
- depression
- mild weight gain
Describe symptoms/presentations seen in the history of a patient with hypothyroidism.
- insidious onset
- cold intolerance
- decreased sweating
- lethargy
- hoarse voice (due to Reinke’s oedema)
- cramps
- dry skin + hair loss
- weight gain, constipation, reduced appetite
- mental slowness, depression
- ataxia, paraesthesia
- menstrual disturbance (menorrhagia, irregular cycles)
- Hx of surgery or radioiodine therapy for hyperthyroidism
- personal/Fx of other autoimmune conditions (e.g. Addison’s, T1DM)
What symptoms/presentations are seen in myxoedema coma?
- severe hypothyroidism usually seen in the elderly
- hypothermia
- hypoventilation
- hyponatraemia
- heart failure
- confusion
- coma
What clinical features are seen on examination of a patient with hypothyroidism?
- hypertension due to decreased peripheral resistance
- hands - bradycardia, cold hands
- head/neck/skin - pale puffy face, goitre, oedema, hair loss, dry skin, vitiligo
- chest - pericardial effusion, pleural effusion
- abdomen - ascites
- neurological - slow relaxation of reflexes, signs of carpal tunnel syndrome
What is a feature you would see in Hashimoto’s thyroiditis on examination?
Firm and non-tender goitre
What is the 1st line investigation for hypothyroidism?
- serum thyroid-stimulating hormone (TSH)
- normal TSH range is 0.4 to 4.0 mIU/L and levels are elevated in primary hypothyroidism
- in sub-clinical disease levels are only mildly elevated - usually <20mIU/L or maybe <10mIU/L
What other investigations do we consider for hypothyroidism (after conducting 1st line serum TSH)?
Bedside:
- fasting blood glucose (may be elevated in T1DM - associated with hypothyroidism)
Bloods:
- TFTs - primary hypothyroidism (high TSH low T3/T4) vs secondary hypothyroidism (low TSH low T3/T4)
- antithyroid peroxidase antibodies - elevated in most patients with autoimmune thyroiditis, not routinely ordered
- FBC - normocytic anaemia associated with hypothyroidism
- serum cholesterol - often elevated –> high CVD risk
- U&Es - may show low sodium
What may TFT results be during normal pregnancy?
- normal TSH, fT4 and fT3 but raised total T3 and T4
- due to high concentration of thyroid-binding globulins
If we suspect pituitary insufficiency in a patient with hypothyroidism, what do we do next?
MRI
What antibody is present in Hashimoto’s thyroiditis?
Anti-TPO
What electrolyte can be affected in hypothyroidism?
Sodium - can get euvolaemic hyponatraemia
What do you see in sick euthyroid syndrome?
Low T3/T4 and normal TSH with acute illness
What is the diagnostic criteria for hypothyroidism?
- TFTs
- clinical
What are some differential diagnoses for (primary) hypothyroidism?
- secondary hypothyroidism - with/without other symptoms of hypopituitarism e.g. hypogonadism and secondary adrenal insufficiency, papilledema and visual field deficits, low TSH, MRI
- depression
- Alzheimer’s - cognitive dysfunction in hypothyroidism responds to thyroid replacement therapy
- anaemia - hypothyroid and anaemic patients often have fatigue and dyspnoea on exertion, associated with concurrent autoimmune conditions e.g. pernicious anaemia, TSH
What is the 1st line treatment for primary hypothyroidism in healthy patients <65?
Levothyroxine
- 1.6mg/kg/day orally adjust dose in increments of 12.5 to 25mg to normalise TSH
- 50-100mg/day
- adjust dose to TFTs but do not suppress
- important to rule out underlying adrenal insufficiency before starting thyroid replacement therapy - can precipitate Addisonian crisis
- lifelong
What is the 1st line treatment for primary hypothyroidism in patients with pre-existing coronary artery disease or age >65?
Low-dose levothyroxine (25-50mg orally once daily, adjust dose in increments of 12.5 to 25mg every 4-6 weeks)
(Levothyroxine therapy may exacerbate angina in patients with CAD)
What is the 1st line treatment for sub-clinical hypothyroidism with TSH>10mIU/L? (and TSH 5.5-10)
Low-dose levothyroxine (50-75mg/day, adjust dose in increments of 25-50mg to normalise TSH)
Repeat TFTs in 3-6 months
In patients >65/asymptomatic - observe and repeat TFTs in 6 months
In subclinical hypothyroidism with TSH 5.5-10mU/L: offer patients <65 a 6 month trial of levothyroxine if TSH remains at that level on 2 separate occasions 3 months apart and they have hypothyroidism symptoms
What should be checked regularly in hypothyroid patients receiving levothyroxine?
TSH should be checked annually - poor compliance = raised TSH and normal T4
How is levothyroxine dose affected in pregnancy?
Should be increased up to 50% as early as 4-6 weeks into pregnancy
What risk does overreplacement with thyroxine have?
Increased risk of osteoporosis (/ iatrogenic hyperthyroidism)
How do we advise patients taking levothyroxine who also are taking iron/calcium supplements?
Take iron/calcium 4 hours apart from levothyroxine as they can reduce levothyroxine absorption
What do we give patients with amiodarone-induced hypothyroidism?
Give levothyroxine and can continue amiodarone
How do we treat myxoedema coma?
- oxygen
- rewarming
- rehydration
- IV T4 (levothyroxine) and T3 (liothyronine - faster onset of action)
- IV hydrocortisone
- treat underlying cause e.g. infection
What are some side effects of levothyroxine therapy? (4)
- hyperthyroidism (due to over-treatment)
- reduced bone mineral density
- worsening of angina
- atrial fibrillation
What are some complications of hypothyroidism?
- myxoedema coma - older untreated patients with multiple comorbidities, mortality rate 80%
- angina - high initial dose of levothyroxine in patients with CAD
- over-treatment –> AF, osteoporosis
- complications in pregnancy e.g. pre-eclampsia, perinatal mortality, recurrent miscarriage, foetal neurological maldevelopment
- Hashimoto’s thyroiditis –> MALT lymphoma
What is the prognosis for patients with hypothyroidism?
- lifelong levothyroxine required
- myxoedema coma has mortality rate of 80%
