Chem Path: Thyroid Flashcards
Explain how TSH causes thyroxine (T4) production
TSH causes iodide uptake into the thyroid. Iodide is converted to iodine by thyroid peroxidase. Iodine is then taken into the cells via thryoglobulin. Iodine molecules are then joined together to form T4. T4 is released into the bloodstream and is then converted to T3 in the peripheries.
Apart from TSH what else helps with the uptake of iodide into the thyroid cells?
Na/K/ATPase pump
Which proteins is T4 bound to?
TBG, albumin
What is the cause of primary hypothyoridism?
thyroid gland itself
What is the cause of secondary hypothyoridism?
Pituitary
What are the 3 most common causes of hypothyroidism?
Hashimoto’s - autoimmune
Atrophic
Post Grave’s due to over treatment
Which drugs cause of hypothyroidism
amioderone
lithium
What are the clinical symptoms of hypothyroidism
Everything is slow and low
Hyponatraemia
Normocytic anaemia
What investigations for hypothyroidism
TSH and T4 levels Thyroid peroxidase anitbodies B12 levels for pernicious anaemia IgA Coeliac antibodies Early morning cortisol and adrenal antibodies for Addison's
Why would you do an ECG for hypothyroidism?
If they have underlying cardiac disease, giving them T4 can increase their myocardial contractility
What can excess T4 cause?
Osteopaenia and AF
What is subclinical hypothyroidism
Normal T4 but high TSH
What would you check for in subclinical hypothyroidism
TPO antibodies. If present, patient can develop thyroid disease
What is subclinical hypothyroidism associated with
Hypercholesterolaemia
How do thyroid levels change in pregnancy and why
HCG acts like TSH and causes a rise in T4
TBG levels also increase as they are under the influence of oestrogen
Later in pregnancy as HCG levels drop, so will T4 and therefore TSH will rise
Within how many hours of birth should the Guthrie test be done in a neonate and why?
48-72 hours
To avoid measuring maternal TSH
What happens in sick euthyroid
Thyroid shutdown so low T4 and normal/high TSH
What are the 3 most common causes of hyperthyroidism?
Grave’s - Anti TSHR antibodies
Toxic multinodular goitre
Single toxic adenoma
How can you diagnose all of the 3 causes of hyperthrioidism
Technetium scan - All 3 would have uptake
What is subacute thyroiditis
Thyroid stimulated to secrete excess T4
What is post partum thyroiditis
After pregnancy, the thyroid is attacked by antibodies that the mum has made
What is common for both subacute thyroiditis and post partum thyroiditis
Low uptake on technetium scan
What can cause silent thyroiditis and what would T4 and TSH levels be like?
Amioderone
High T4 and low TSH
What is struma ovarii?
Ovarian tumour that produced T4
What are teh clinical features of thyrotoxicosis
Low TSH
High T4 and T3
Thyroid antibodies
How to manage thyrotoxicosis?
Beta blocker
ECG to monitor fast AF
DEXA scan
What does radioactive iodine do?
Taken up by the thyroid and destroys it slowly
What do you need to stop if you take radioactive iodine
Thionamides
What are the side effects of radioactive iodine
Makes Grave’s eye disease worse
Thyroid storm
Tracheal storm
What do thionamides do?
Prevent iodide to iodine conversion
Give some examples of thionamides
Carbimazole
Propylthiouracil
What are some side effects of thionamides
Rash
Agranulocytosis - sore throat fever (neutropaenia) - Do FBC immedeately
What are the 2 ways thionamides can be used?
1 - Titrated carefully to ensure thyroid is workign optimally
2-Render the thyroid completely useless and supplement T4
What does potassium perchlorate do?
Stop iodine intake into the thyroid before surgery
What happens in thyroiditis?
Pain in the neck
Sudden inflammation leading to sudden release of T4
Thyroid stops working
Need long term T4 supplement
Tend to present with high TSH and low T4
What are the 2 types of thyroid carcinomas
papillary
Follicular
How are thyroid cancers treated?
Removed
High dose radioiondine to remove any remaining cells
High dose thyroxine to lower TSH levels so that it does not stimulate any remaining cells
What are some tumour markers in thyroid cancers?
Thyroglobulin
High levels of TSH if cancer cells remain
What are some tumour markers in medullary thyroid carcinomas
Calcitonin
CEA
What type of condition is medullary thyroid carcinomas associated with
MEN2
What conditions does MEN 2 cause
Thyroid and parathyroid tumours , phaeochromocytomas
What conditions does MEN 1 cause
Pituitary, parathyroid and pancreas
