Thyroid Lecture Flashcards
Anatomy of thyroid gland
- 2 lobes
- Isthmus connects
- Over trachea, just below cricoid cartilage, extends up to base of thyroid cartilage
- Develops from floor of pharynx
- Descends –> thyroglossal duct
Phsyiology of thyroid gland
- Iodine is substrate for hormone synthesis
- Thyroid produces all circulatory T4 and 20% T3 (remainder is converted from T4 in extraglandular tissue)
How is T3 and T4 transported?
- Almost entirely bound
- Proteins such as TBG, TTR and albumin
Thyroxine binding globulin, transthyretin
What form of thyroid hormone is able to act on tissues?
Only free hormone
Revise thyroid function test results
:)
Causes of low or normal TSH with low T3/T4
- Central hypothyroidism - pituitary problem
- Isolated TSH deficiency
- Assay interference
- Non-thyroid illness
Causes of high or normal TSH with high T3/T4
- Assay inteference
- Thyroxine replacement therapy
- Drugs eg amiodarone and hepatin
- Non thyroid illness
- TSH secreting pituitary adenoma
- Reistance to thyroid hormone
- Disorders of thyroid hormone transport/metabolism
Specifc signs of Graves
- Eye disease - lid retraction, exopthalmos, paralysis of eye muscle
- Dermopathy
- Acropachy
- Lymphoid hyperplasia
Dr Omer said Graves is only one to have skin and/or eye disease
Symptoms of thyrotoxicosis
- Palpitations
- Shaking
- Sweating
- Dyspnoea
- Weakness
- Diarrhoea
- Dysmenorrhoea
- Heat intolerance
- Weight loss
- Irritable
- Insomnia
Signs of thyrotoxicosis
- Tachycardia/AF
- Tremor
- Hyperkinesia
- Hyper-reflexia
- Palmar erythema
- CHF
- Chorea
- Period paralysis
- Psychosis
- Goitre
Causes of thyrotoxicoss - primary
- Graves disease
- Hashitoxicosis (hyperthyroid phase of those with Hashimotos thyroiditis)
- Nodular thyroid with autonomous function
- Thyroiditis
Causes of thyrotoxicosis - secondary
- Pituitary TSHoma
- Thyroid hormone resistance
How else can thyrotoxicosis occur?
- Overtreatment for hypothyroidism
- Thyrotoxicosis factitia - accidental/deliberate thyroxine ingestion
- Ectopic - trophoblastic tumours, stoma ovari
Thyrotoxicosis diagnostic pathway
- Check TSH, T4, T3
- Check TSH receptor antibodies
- If present= Graves if not –> Technitium scan to see uptake
- Increased = Graves
- Patchy/single nodule = toxic multinodular goitre/toxic nodule
- Reduced = thyroiditis
Treatment for Graves thyrotoxicosis
- Either dose titration or block and replace:
- Carbimazole - 1st line
- Propylthiouracil - used in pregnancy
- Beta blockers - propranolol
Management of AF in hyperthyroidism
- Consider anticoagulation,
- Cardiovert after 4 months euthyroid
Side effects of carbimazole or propyltiouracil
- Agranulocytosis - if get sore throat and fever within 24hrs need FBC to see if low
- Rash
- Allergy
- Arthralgia
- Abnormal LFTs
- Liver damage with PTU
Definitive treatment options for thyrotoxicosis
- Radioactive iodine
- Surgery
Consider these later on in Graves but earlier in toxic nodule/multinodular as high chance of relapse with this.
Treatment for thyroiditis
- Carbimazole/propylthiouracil if needed
- Thyroid usually tends to settle down quickly though
- Beta blockers for symptomatic relief
- Steroids may be needed
Treatment for secondary hyperthyroidism
- Trans-sphenoidal surgery
- Pituitary radiotherapy
- Somatostatin analogue
Symptoms of hypothyroidism
- Fatigue
- Confusion
- Cold intolerance
- Menorrhagia
- Weight gain
- Dry skin
- Hoarse voice
- OSA
- Depression
- Carpal tunnel
Signs of hypothyroidism
- Bradycrdia
- Bundle branch block/complete heart block
- Prolonged relaxation phase of reflexes
- Peripheral neuropathy
- Cold, dry palms
Investigations (other than thyroid) results for hypothyroidim
- Hyponatraemia
- Hyperlipidaemia
Primary causes of hypothyroidism - non goiturous
- Post radioactive iodine
- Congenital developmental defect
- Atrophic thyroiditis
- Post radiation
Primary causes hypothyroidism - goitourous
- Hashimotos
- Iodine deficiency
- De Quevains
- Postpartum haemochromatosis
- Drugs - amiodarone, Sunitinab, Rifampicin
- Maternally transmitted
Secondary causes of hypothyroidism
- Panhypopituitarism
- Isolated TSH deficiency
- Hypothalamic congenital
Treatment of hypothyroidism
Thyroxine
Often problems with compliance, always check this if thyroid bloods seem to be unresponsive to treatment and you are thinking about increasing dose
Check TSH every 6 weeks then yearly
When to take levothyroxine
- Morning - 1st thing
- Empty stomach
- 30 mins prior to food/other medications
What can affect thyroxine absorption?
- Coeliac
- H-pylori
- Lactose intolerance
- Can do thyroxine absorption test when you administer high dose in day case and they measure blood levels
When is T3 given for hypothyroidism?
NOT OFTEN:
* It is very expensive
* Not a lot of benefit shown
* But in some patients who T4 and TSH is fine but are still symptomatic, this may help
What is myxoedema coma?
- Severe hypothyroidism
- = hypothermia
- neurological changes - confusion/coma
- Low, shallow breathing
- CVS - bradycardia, hypotension
Management of myxoedema coma
- Warm, humidified O2
- IV access
- IV fluids
- Passive external warming - 0.5 degrees per hour
- Identify precipitating factor - blood cultures, correct electrolyte imbalance, hypoglycaemia etc?
- NG T4
- If no improvement, seek specilaist advice to give T3 IV
- Give hydrocortisone if low cortisol
*
Management of thyroid storm
- O2
- IV fluids
- Paracetamol
- Chlorpromazine for agitation
- Identify precipitating factors - blood cultures, correct electrolytes, hypotension etc
- PTU - blocks T4 to T3 conversion
- Potassium iodide - stops hormonal release
- Beta blockers
- High dose steroids - block T4 to T3
- Cholecystramine - reduces enterhepatic circultation of thyroid hormone
- Plasmapheresis/peritoneal dialysis if resistant to medical manageemnt
