Thyroid Flashcards
How is most of t3 and t4 found?
Peripherally bound to thyroxine binding protein (TBG)
Free t3 and t4 are better measured of these hormones as TBG varies and increased TBG means more total t3 and t4.
TBG increased by pregnancy, oestrogen therapy and hepatitis
TBG decreased in nephrotic syndrome and malnutrition (protein loss), drugs, chronic liver disease and acromegaly
High TSH and low T4
Primary Hypothyroidism
High TSH and normal t4
Treated or subclinical primary hypothyroidism
High TSH and high t4
TSH secreting tumour or thyroid hormone resistance
Low TSH and high t4 or t3
Primary Hyperthyroidism
Low TSH and normal t3 and t4
Subclinical hyperthyroidism
Low TSH and low t4
Central aka secondary hypothyroidism - hypothalamus or pituitary problem
Low TSH, t3 and t4
Sick euthyroid system or pituitary disease
Normal TSH, abnormal t4
Consider changes in thyroid- binding protein,
What test can also be raised in autoimmune thyroid disease?
Anti-thyroid peroxidase antibodies or antithyroglobulin antibodies may be increased
Eg. Hashimotos, graves
What 2 scans can be done to look at the thyroid?
- USS can distinguish between cystic and solid nodules
Cystic usually but not always benign, solid possibly malignant - Isotope scan - few neutral and almost no hot modules are malignant but a cold module can be malignant (20%)
What is the thyroid system?
Thryotropin-releasing hormone secretion from hypothalamus stimulates thyroid-stimulating hormone from anterior pituitary.
This causes release of t3 and t4 from the thyroid gland - mostly t4 which is the peripherally converted to the more active T3.
T3 and T4 negativity feedback on TSH production
Which patients should you screen for thyroid disease? X6
- AF patients
- hyperlipidaemia patients (high cholesterol in hypothyroidism)
- DM
- women with type 1DM during 1st trimester of pregnancy or post-delivery have 3x increased risk of postpartum thyroid dysfunction
- patients on amiodarone (thyroid abnormalities hypo and hyper in 14-18% of patients) or lithium (causes hypothyroidism - goitre in 40-50% of patients)
- patients with downs or turners syndrome or Addison’s disease
Symptoms of thyrotoxicosis
Diarrhoea, weight loss, increased appetite
Overactive, sweats and heat intolerance
Palpitations and tremor
Irritability and labile emotions
Oligomenorrhoea
Signs of thyrotoxicosis
Pulse - fast or irregular
Warm moist skin and thin hair
Fine tremor and palmar erythema
Onycholysis
Lid lag and lid retraction
Thyroid goitre or nodules or bruit
3 signs of Graves’ disease
Eye disease (exophalmos and ophthalmoplegia)
Pretibial myxoedema - oedematous swellings above lateral malleoli
Thyroid acropachy - clubbing, painful finger and toe swelling and periosteal reaction in limb bones
What blood cell/electrolyte manifestation do you get in hyperthyroidism x4
Mild neutropenia
Raised ESR
Calcium raised
LFTs raised
Prevalence of Graves
0.5% - 5/1000
2/3 of hyperthyroidism
F:M ratio of Graves
F:M = 9:1
Associated with other autoimmune diseases eg. t1dm, addison’s, vitiligo
Typical age of presentation of Graves
40-60 years
younger if maternal family history
Cause of Graves disease
Autoimmune hyperthyroidism
Circulating IgG autoantibodies binding to and activating g-protein coupled thyrotropin receptors
Causing increased thyroid hormone production and smooth enlargement
The autoantibodies also react with orbital autoantigens - eye disease - cause retro-orbital inflammation and lymphocyte infiltration
Triggers of Graves
Stress, infection, childbirth
8 other causes of hyperthyroidism
1) Toxic multi-nodular goitre
- mostly in elderly and iodine deficient areas - nodules secrete thyroid hormones - surgery for compressive symptoms
2) Toxic adenoma
- solitary nodule producing t3 and t4 - nodule is hot and rest suppressed on isotope scan
3) Ectopic thyroid tissue - either metastatic follicular thyroid cancer or struma ovarii - ovarian teratoma with thyroid tissue
4) Exogenous
- Iodine excess (iodine needed for thyroid hormone synthesis therefore can stimulate increased production especially in subacute)
- Contrast media
- Levothyroxine
5) Subacute de Quervain’s thyroiditis
- self-limiting post viral - high temperature, low uptake on isotope scan - treat with NSAIDs
6) Amiodarone
7) Postpartum
8) TB - rare
Immediate treatment of hyperthyroidism
Beta-blockers for rapid control of symptoms - AF
Treatment of hyperthyroidism with anti-thyroid medication
Carbimazole - active form is methimazole
Prevents thyroid peroxidase enzyme from coupling and iodinating tyrosine residues on thyroglobulin
Prevents T3 and T4 production
Side effects = agranulocytosis
Can either give dose and titrate until correct dose
Or can block completely with carbimazole and then replace with thyroxine - less chance of iatrogenic hypothyroidism
Treatment of Graves
Maintain on carbimazole regimen for 12-18months and then withdraw
50% relapse and therefore need surgery or radioiodine
2 other types of non-medical therapy for hyperthyroidism
Radioiodine (need to avoid pregnancy for 4 months and contact with pregnant women or small children for 2 weeks)
or thyroidectomy
Both risk hypothyroidism
Surgery also risk hypoparathyroidism and damage to recurrent laryngeal nerve
Complications in hyperthryoidism 3 x cardiac and 4x other
AF, angina, heart failure
Osteoporosis
Opthalmoplegia
Gynaecomastia
Thyroid storm
Prevalence of thyroid eye disease in Graves patients and 3 other factors
25-50%
Main risk factor is smoking
Eye disease doesn’t correlate with thyroid disease
Can worsen with radioiodine treatment
Symptoms of Graves thyroid eye disease
Eye discomfort, grittiness, increased tear production
Photophobia, diplopia, decreased visual acuity
RAPD - may mean optic nerve compression
Compression not related to protrusion - often opposite
Signs of Graves eye disease
Exophthalmos, proptosis
Conjunctival oedema
Corneal ulceration
Papilloedema
Opthalmoplegia
Treatment of bad eye disease
High dose steroids - if opthalmoplegia or gross oedema
IV methylprednisolone
Another name for hypothyroidism
Myxoedema
Prevalence of hypothyroidism
4/1000 (less than hyper)
Male to female ratio of hypothyroidism
1:6 …M:F
Symptoms of hypothyroidism
Tired/sleepy, lethargic, cold disliking
Weight gain, constipation and menorrhagia
Low mood, decreased memory and cognition and dementia
Myalgia, cramps and weakness
Hoarse voice
Signs of hypothyroidism
BRADYCARDIC
Bradycardic
Reflexes relax slowly
Ataxia - cerebellar
Dry + thin skin/hair
Yawning/drowsy/coma
Cold hands + low temp
Ascites - non-pitting oedema +/- pericardial or pleural effusion
Round puffy face/double chin/obese
Defeated demeanour
Immobile +/- ileus
CCF
also goitre, myopathy and neuropathy
What is high in hypothyroidism?
Cholesterol and triglycerides Also TSH (T4 low) Unless rare secondary in which case both TSH and T4 are low
What is the biggest cause worldwide of hypothyroidism?
Iodine deficiency
Iatrogenic causes of hypothyroidism
Post thyroidectomy or RI treatment
Drug-induced - antithyroid drugs, amiodarone, lithium, iodine
3 other causes of hypothyroidism
1) Primary atrophic hypothyroidism - f:m = 6:1, more common in elderly - diffuse lymphocytic infiltration causes atrophy and fibrosis of the gland - no goitre - can also be end stage of diseases such as hashimotos
2) Hashimotos thyroiditis
- goitre due to lymphocytic and plasma cell infiltration
- commoner in women 60-70
- may be hypothyroid or euthyroid
- rarely an initial period of hyperthyroid - hashitoxicosis - autoantibody titres are very high
3) Subacute thyroiditis
- Temporary hypothyroidism after hyperthyroid phase
- can occur in de quervains and post-partum thyroiditis
Associations of hypothyroidism
Autoimmune Turners and Downs CF Primary biliary cirrhosis Ovarian hyperstimulation
POEMs syndrome
Dyshormogenesis - genetic defect in hormone synthesis
Treatment of hypothyroidism in healthy and young
Levothyroxine (T4)
50-100ug/24hr
Review at 6 weeks
Treatment of hypothyroidism in elderly or IHD
Start with 25ug of levothyroxine and titrate up according to TSH levels
Caution because levothyroxine can precipiate angina or MI
Amiodarone features
It is an anti-arrhythmic drug which is structurally like T4 and is iodine rich
2% of patients get thyroid problems using it
Can be hypo or hyper
Has 80 day half life therefore symptoms persist post-withdrawal
What is myxoedema coma?
Severe hypothyroidism usually seen in elderly
Hypothermia, hypoventilation, hyponatraemia, heart failure, confusion and coma
Treat with IV T3/T4 + IV hydrocortisone in case due to hypopituitarism
What may be low in serum in hypothyroidism
Sodium
Treatment of acute hyperthyroidism crisis
Propylthiouracil, propanolol, IV hydrocortisone (inhibits peripheral conversion of T4 to T3)
Potassium iodide or lugols iodine
Rehydrate and control temperature
F/U needed when changing levothyroxine dose
8-12weeks
TSH level aim when treating hypothyroidism
0.5-2.5
Management of hypothyroidism in pregnancy
Increase dose by 25-50micrograms because increased demand in pregnancy
Side effects of levothyroxine therapy
Worsening angina
Decreased Bone mineral density
Hyperthyroidism
AF
Which syndromes/diseases are associated with thyroid disease and what kind
Hypothyroid - downs, turners and addissons disease
