Hyperthyroidism Flashcards
Definition of hyperthyroidism
Hyperthyroidism reflects an increased level of circulating thyroid hormone leading to raised metabolic rate and sympathetic nervous system activation.
Thyroid function physiology
- Hypothalamus produces thyroid-releasing hormone (TRH)
- Which stimulates the anterior pitiuitary to release thyroid-stimulating hormone (TSH)
- Which acts on the thyroid which produces T4 and some T3
- T4 is activated (converted to T3) by peripheral tissue: liver, kidney, brain and skeletal muscle
- Negative feedback to hypothalamus
Pathophysiology of primary hyperthyroidism
- Excessive production of T3/T4 by the thyroid gland
- Thyroid gland pathology
- Most common subtype
Pathophysiology of secondary hyperthyroidism
- Stimulation of the thyroid gland by excessive TSH
- Originates due to pathology of the pituitary or hypothalamus
- May also be secondary to a TSH-secreting tumour
Common causes of primary hyperthyroidism
- Graves’ disease
- Toxic multinodular goitre
- Toxic adenoma (single autonomous functional nodule)
- Thyroiditis
- Transient hyperthyroidism occurring before hypothyroidism due to Hashimoto’s and De Quervain’s thyroiditis
- Subclinical hyperthyroidism
- Normal T3/T4, low TSH
- Typically due to toxic multinodular goitre or Graves’ disease
- Drugs
- Amiodarone causes both hyperthyroidism and hypothyroidism
Pathophysiology of Graves’ disease
- Anti-TSH receptor antibodies
- Most common cause of hyperthyroidism (75%)
- Diffuse goitre and thyroid eye signs
Pathophysiology of toxic multinoduar goitre
- Iodine deficiency
- Compensatory TSH secretion
- Nodular goitre formation
- Nodules become TSH-independent and over produce thyroid hormones
Secondary hyperthyroidism causes
-
Pituitary adenoma
- TSH-secreting pituitary adenoma
-
Ectopic tumour
- hCG-secreting tumours (eg choriocarcinoma)
-
Hypothalamic tumour
- Excessive TRH secretion
- Rare cause of hyperthyroidism
Risk factors for hyperthyroidism
- Femal gender: particularly for Graves’ disease
- Family history
- Other autoimmune conditions
- Smoking: increases risk of Graves’ eye disease
- Trauma to the thyroid gland: including surgery
- Drugs: eg Amiodarone
Symptoms of hyperthyroidism
- Weight loss
- Heat intolerance and sweating
- Palpitations
- Menstrual irregularity
- Anxiety
Signs of hyperthyroidism
- Postural tremor
- Palmar erythema
- Graves’ disease
- Thyroid acropachy
- Pretibial myxedema
- Eye signs
- Exophtalmos
- Opthalmoplegia
- Lid lag and retraction
- Goitre
- Hyperrelfexia
Which autoantibodies are present in Graves’ disease?
- Anti-TSH receptor (90-100%)
- Anti-TPO (70-80%)
- Anti-thyroglobulin (20-40%)
Primary investigations in hyperthyroidism
- Thyroid function tests (TFTs): first line investigation
- Antibodies: anti-TSH receptor antibodies (95%) and anti-TPO most often raised in Graves’ disease
Causes of disease if:
TSH low, T4 high
TSH low, T4 normal
TSH high/normal, T4 high
- TSH low, T4 high: primary hyperthyroidism
- TSH low, T4 normal: sub clinical hyperthyroidism
- TSH high/normal, T4 high: secondary hyperthyroidism
Investigations to consider in hyperthyroidism
- Ultrasound: if thyrotoxic with a palpable thyroid nodule
- Technetium radionuclide scan: performed if anti-TSH antibodies are negative
- Glucose: hyperthyroidism is associated with hyperglycaemia
- ECG: hyperthyroidism is associated with atrial fibrillation
Management of hyperthyroidism
- Anti thyroid medication
- Carbimazole: usually first line
- Propylthiouracil: first line pre-pregnancy or in the first trimester
- Titration regime: titration down to lowest effective dose
- Block and replace regimen: levothyroixine is added as needed
- Radioiodine
- First line definitive management in more-than-mild Graves’ and toxic multinodular goitre
- Surgery: total or hemithyroidectomy
- Requires pre-operative optimisation (aiming for euthyroidism)
- Consider propranolol for symptomatic relief
Contraindications for radioiodine therapy
- Pregnancy and breastfeeding
- Thyroid eye disease
- < 16 years
Advice for patients post radioiodine treatment
- Avoid close contact with pregnant women and children for 3 weeks
- Avoid becoming pregnancy for 6 months
- Avoid fathering children for 4 months
- Patients will often require long term levothyrxine after radioiodine therapy
Indication for total or hemithyroidectomy
Indicated in those at high risk of recurrent hyperthyroidism or when other options fail.
Hemithyroidectomy is preferred for a single thyroid nodule.
Complications of thyroidectomy
- Hypothyroidism
- Hypoparathyroidism
- Recurrent laryngeal nerve palsy
Complications of hyperthyroidism
- Cardiovascular: heart failure, atrial fibrillation
- Musculoskeletal: osteoporosis, proximal myopathy
- Thyrotoxic crisis
- Iatrogenic:
- Agranulocytosis and neutropaenic sepsis: secondary to carbimazole
- Hepatotoxicity: secondary to propylthiouracil
- Congenital malformations: carbimazole in first trimester
- Foetal goitre and hypothyroidism: any anti thyroid medication in pregnancy at high doses
Thyroiotoxic crisis (thyroid storm) aetiology
- Untreated hyperthyroidism
- Often triggered by an infection
Thyroid storm clinical features
- Tachycardia: often >140 BPM, with or without AF
- High temperature: often > 40 degrees
- Diarrhoea and vomiting
- Jaundice
- Confusion or mental agitation
Thyroid storm mortality rate
- With treatment: 20-40%
- Untreated: up to 75%
Investigations for thyroid storm
- TFTs: elevated T3 and T4, suppressed TSH
- Screen for the cause: eg an infection screen
- Full set of bloods: FBC, U&Es, LFTs, bone profile, blood glucose
- CXR
- Arterial blood gases
Management of thyroid storm
- IV fluids: replace losses
- NG tube insertion: if vomiting
- Cooling: sponging and paracetamol
- Antithyroid drugs: propylthiouracil is often preferred
- Corticosteroid: IV hydrocortisone
- Beta-blocker: propranolol PO or IV over 10 minutes
- Oral iodine: Lugol’s iodine offered >1 hour after propylthiouracil
- Sedation: if required, use chlorpromazine
- Plasma exchange or thyroidectomy: in refractory patients
