Thyroid Disease

Question 1

Thyroid basic anatomy

Answer 1

• 2 lobes
• joined by isthmus
• superior and inferior thyroid artery supply
• isthmus 2 fingers above sternal notch
• impalpable unless 2-3x normal size
• follicular cells around colloid pool
• C cells among follicular cells produce calcitonin
• 4 parathyroid glands behind thyroid

Question 2

Thyroid Hormone synthesis

Answer 2

• iodine in blood imported into follicular cell via Na iodine symporter
• into follicular lumen
• in colloid ER produces thyroglobulin which is passed into follicular lumen
• tyrosine bound to Tg has iodines added to it by TPO
• tyrosine has 4 idoines added = T4 (levothyroxine)
• T4 passed back through cell and excreted into bloodstream
• carried in blood bound to albumin
• T3 is active thyroid hormone
• most T4->T3 conversion happens in cell where thyroid hormone acts via deiodination but some happens in follicular cell

Question 3

Thyroid Hormone control

Answer 3

• positive and negative feedback loops
• hypothal secretes TRH -> pituitary secretes TSH -> binds to TSH receptor on thyroid gland -> thyroid hormone production
• T3 and 4 feedback on pituitary and hypothalamus downregulating TRH and TSH secretion

Question 4

How much T4 is there?

Answer 4

50% converted to T3 and other 50% left inactive

Question 5

Thyroid hormone action and function

Answer 5

T3 active

• diffuse through membrane and bind to THR (nuclear receptor)
• gene transcription changes
• acts on majority of cells
• effects basal met. rate, catecholamine sensitivity
• important for neural dev. in fetus

Question 6

Thyrotoxicosis = presentation and history questions

Answer 6

• overactive thyroid
• tired, anxious, sweating
  CVS - palpitations, AF, heat intolerance
  ABDO - weight loss, frequency, increased appetite
  GU - oligomenorrhoea
  NS - tremor, graves ophthalmopathy, muscle weakness, emotional
  PMH = autoimmune, IHD
  DH = amiodarone, lithium, IF, TKIs, retrovirals (contain or mimic iodine)
  FH = autoimmune
• onset = acute or insidious

Question 7

Thyrotoxicosis Exam

Answer 7

• general = agitated, thin, tremor, vitiligo or other autoimmune
• thyroid = goitre, smooth/nodular
• CVS = tachycardia, AF
• NS = id retraction, lid lag, brisk reflexes, proximal myopathy
• other = Graves’ (eyes, shins, hands), cardiac failure, bp, fever

Question 8

Investigations of thyrotoxicosis

Answer 8

TFT = free T4, TSH, T3

• free thyroxine T4 elevated
• TSH undetectable
• sometimes T3 thyrotoxicosis but not as much
• thyroid antibodies to prove autoimmunity
• gastric parietal cell antibodies as thyroid autoimmunity = pernicious anaemia B12 levels

Question 9

Differentials of thyrotoxicosis

Answer 9

MORE COMMON
- grave's disease (autoimmune thyroid condition with TSH receptor antibodies causing it)
- toxic multi-nodular goitre (low iodine, loss of reg mechanisms)
LESS COMMON
- toxic adenoma
- destructive thyroiditis
- excess iodine
- drugs
- thyroid hormone and TSHoma

Question 10

Grave’s

Answer 10

• autoimmune condition
• thyroid dysfunction (thyroid stimulating antibodies)
• ophthalmopathy
• pre tibial myxoedema
• acropachy
• diffuse smooth goitre
• bruit
• FH autoimmune
• patient autoimmune
• thyroid stimulating antibodies in blood

Question 11

Grave’s ophthalmopathy

Answer 11

• smoker
• pain
• tearfulness & grittiness
• diplopia
• visual acuity
• loss colour vision
• redness
• proptosis

Investigations = MRI orbits, TFT
Treatment = steroids, surgery, radiotherapy

Question 12

Mechanism of grave’s eyes

Answer 12

• optic nerve compression
• muscles and fat behind eyes = proptosis = stretching of nerve
• apex of orbit less space for nerve and muscles => nerve compressed

Question 13

Thyrotoxicosis treatment

Answer 13

• Medical = carbimazole, propylthiouracil, propanol if acute cases (side effects rash 1 in 100, agranulocytosis 1 in 1000)
• Radioiodine = away from children 1-2w, may get hypothyroidism, worsening eye disease contraindication
• surgery = recurrent laryngeal nerve damage risk, hypothyroid and hypoparathyroidism risk, thyroxine for life

Question 14

Hypothyroidism History and Exam presentation

Answer 14

• general - tired, cold, dry skin and hair
• abdo = weight gain, constipation
• GU = menorrhagia
• puffy
• cold dry skin
• goitre
• bradycardia
• slow relaxing reflexes
• extremes = coma, hypothermia

Question 15

Hypothyroidism Investigations

Answer 15

• TFT = low free T4, elevated TSH
• thyroid antibodies present
• cortisol to ensure normal ACTH reserve
• B12
• consider hypothyroidism 2ndry to pituitary failure if low normal T4 and TSH not elevated

Question 16

Causes of hypothyroidism

Answer 16

• iodine deficiency
• Hashimoto’s thyroiditis
• congenital hypothyroidism
• iatrogenic
• post partum thyroiditis

Question 17

Hypothyroidism treatment

Answer 17

• depends of cause and severity
• possible Addison’s and IHD don’t want sudden change in heart rate, gently reintroduce thyroxine
• thyroxine = titrated to target TSH for each patient
• high TSH still in treatment = intercurrent illness, inadequate dose, malabsorption, non compliance

Question 18

Goitre cause

Answer 18

• any thyroid enlargement
• 2 common types = multi nodular (low iodine area) and autoimmune thyroiditis (graves and hashi)
• other causes = iodine deficiency, neoplasia of thyroid, granulomatous, amyloid

Question 19

Multi-nodular goitre

Answer 19

• lump in neck how long, how sudden
• thyrotoxic
• dysphagia
• cough/dyspnoea/stridor
• sudden enlargement or pain
• size
• retrosternal
• airway compromise
• thyroid function
• lung function
• CXR
• USS
• CT without contrast for retrosternal extension
• watch and wait if small and no symptoms
• surgery = remove whole thyroid as if remove some other side enlarges OR remove nodules