L14 - Thyroid Flashcards
What is the function of thyroid hormones?
- Control of metabolism: energy generations and use
- Regulation of growth
- Multiple roles in development
Which thyroid hormone is the most biologically active one?
T3 is the biologically active hormone
What are the different thyroid hormone binding proteins?
- Serum albumin
- TBG (thyroxine binding globulin)
- Transthyretin
Which thyroid hormone has a greater percentage of being free?
T4 = 0.03% T3 = 0.3%
What would thyroid function tests show for hyperthyroidism?
- LOW serum TSH (thyroid stimulatinf hormone)
- HIGH serum free T4
- HIGH serum free T3
What would thyroid function tests show for hypothyroidism?
- HIGH serum TSH (thyroid stimulating hormone)
- LOW serum free T4
- LOW serum free T3
Which gender is thyroid disease more prevalent in?
- Hyperthyroidism
- Hypothyroidism
- Goitre
Female more common than men
What are the different possible aetiologies of hyperthyroidism?
- Graves’ hyperthyroidism (AI disorder)
- Toxic nodular goitre (single or multinodular)
- Thyroiditis (silent, subacute): inflammation
- Exogenous iodine (external origin)
- Factitious (taking excess TH)
- TSH secreting pituitary adenoma
- Neonatal hyperthyroidism
What are some symptoms of HYPERthyroidism?
- Tachycardia
- Heat sensitivity
- AF
- Shortness of breath
- Tremor
- Myopathy (muscle weakness)
- Weight LOSS
- INC appetite
What is Graves’ disease?
- AI disorder
- Most prevalent AID in UK and US
- Pathogenetic antibodies to TSH receptor on thyroid follicular cells (long acting thyroid stimulators)
- Interplay between genetic and environmental factors
- Environmental factors include: gender, stress, infection, pregnancy or drugs
What are some symptoms of graves disease?
- Anxiety and irritability
- Heat sensitivity
- Weight loss despite normal eating habits
- Goitre (enlargement of thyroid gland)
What are the different possible extra-thyroidal manifestations of the eye from Graves’ disease?
- Lid lag/ retraction
- Conjunctival oedema
- Periorbital puffinesss around the eye
- Proptosis (bulging)
- Ophthalmoplegia (weakness of eye muscles)
What are the different possible extra-thyroidal manifestations of the skin from Graves’ disease? (Dermopathy)
- Pretibial myxoedema
- Acropachy
What is pretibial myxoedema?
- Localised lesions of the skin
- Pretibial meaning myxoedema on the shins (result in swelling and lumpiness)
- Myxoedema is the deposition of hyaluronic acid
What is acropachy?
- Thickening of extremities
- Swelling and clubbing of fingers and toes
- Periostitis (inflammation of periosteum; the CT surrounding bone); most commonly the metacarpal bones
What causes neonatal hyperthyroidism?
- TSH-R antibodies cross the placenta
- Need to control hyperthyroidism in mother during pregnancy
- Mother has or had Graves’ disease
What are the different treatment options for HYPERthyroidism?
- Antithyroid drugs to block hormone synthesis
- Surgical removal of thyroid
- Radioiodine (131I) therapy
What are some of the different anti-thyroid drugs (thionamides)
- CARBIMAZOLE (methimazole)
2. PROPYLTHIOURACIL
How does propylthiouracil work?
Block iodine incorporation and organification through inhibition of thyroperoxidase
What would you need to consider before giving thionamide therapy?
- Rapid control, well tolerated
- Side effects
- Rash, joint pains, sickness
- Agranulocytosis: no WBC, infection risk
- Liver disease - Low cure rate
- (30-40% lower in men)
What would surgery involve when treating hyperthyroidism?
Total thyroidectomy: removal of whole thyroid gland
What are the complications of total thyroidectomy?
- Hypothyroidism
- Hypoparathyroidism: problems with calcium
- Recurrent laryngeal nerve damage
- Bleeding
- Thyroid storm: release of high concentrations of TH in circulation
What would radioactive iodine treatment for hyperthyroidism involve?
- Capsule (fixed dose)
- Highly effective (85% cure)
- Usually pre-treatment with drugs
- May worsen eye disease (treat with steroids)
What are the possible risks of giving iodine-131?
- Hypothyroidism (~60%)
- Cancer
- Infertility
- Teratogenesis (contra-indicated in pregnancy and breastfeeding - congenital malformations are produced in the embryo or foetus)
What are the treatment aims of hyperthyroidism?
- To relieve symptoms
- To restore T3 and T4 values within normal range
- To obtain long-term normal thyroid function
What is the prognosis of patients after hyperthyroidism treatment?
- 30% of patients with Graves’ disease have normal thyroid function long-term following drugs
- 131-I and surgery assoc with >50% risk of long-term hypothyroidism
What are the different possible aetiologies of HYPOthyroidism?
- Autoimmune - Hashimoto’s thyroiditis (TPO and Tg antibodies - genetic predisposition)
- After treatment for hyperthyroidism
- Subacute/ silent thyroiditis
- Iodine deficiency
- Congenital (thyroid agenesis/ enzymes defects)
What is the main source of iodine in the UK?
From milk and dairy products
Which group of people are more likely to suffer from iodine deficiencies?
Vegans
What is cretinism?
Causes?
- Congenital HYPOthyroidism (underactivity of thyroid gland at birth)
- Deficiency of iodine in mother’s diet during pregnancy
- Growth retardation
- Developmental elay
- Abnormal features
What are some symptoms of HYPOthyroidism?
- Bradycardia
- Heart failure
- Pericardial effusion (abnormal acc of fluid in the pericardial cavity –> inc intrapericardial pressure –> negatively affect heart function)
- Weight gain
- Constipation
- Myxoedema
- Vitiligo
- Cold intolerance
What tablet is typically prescribed for hypothyroidism?
LEVOTHYROXINE
What is the goal of therapy for hypothyroidism?
- Restore patients to euthyroid state
- Normalise serum T4 and TSH concentrations
What would you do in an investigation of thyroid nodules/ goitre?
- Assessment of thyroid function
- Serum TSH
- Serum free T3/T4 - Assessment of thyroid size
- Symptoms
- X-ray thoracic inlet
- CT or MRI of neck
- Respiratory flow loop - Assessment of thyroid pathology
- Radionuclide scanning (radioisotope scan)
- Ultrasound scanning
- Fine needle aspiration cytology
Describe what the expiratory respiratory flow loop would look like if there was an intrathoracic obstruction
- Expiratory plateau
Describe what the inspiratory respiratory flow loop would look like if there was an extrathoracic obstruction
- Inspiratory plateau
Why can respiratory flow loops be used to assess thyroid size?
- The thyroid gland lies close to the boundary between extra and intra-thoracic sections of the trachea
- If large goitre –> press against trachea –> cause narrowing/ deviation of upper airway –> experience difficulty in breathing or shortness of breath
What is the role of ultrasound scanning when investigating the thyroid gland?
- Differentiation of solid from cystic nodules
- Differentiation of single from multiple nodules (superior to palpation)
- Criteria suggestive of malignancy (irreg margin, calcifications, solid, hypo-echoic)
- Guidance of fine needle aspiration
What are the different possible aetiologies of thyroid cancer?
- External irradiation
- Iodine deficiency
- Oncogene expression
- Genetic factors
What are the different possible managements of thyroid cancer?
- Surgery
- Total thyroidectomy
- Partial thyroidectomy (lobectomy) - Radioiodine ablation
- Thyroxine suppression
- Measurement of serum thyroglobulin
