Hypothyroidism (E&M) Flashcards
(39 cards)
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
