Amine Hormones Flashcards
Cause of exophthalmos in TED
Due to increase GAGs via TSH receptors when TRAbs bind to them.( Due to production of fibroblasts).
Also due to adipocytes producing adipose tissue.
All these causes swelling in muscles and tissue behind the eye.
Cause of thyroid signs in pregnancy despite low TRab
Due to high hCG that induces transient hyperthyroidism - increases T 3 and T4 and decreases TSH
Causes of temporary thyoriditis
Viral or pospartum,
Causes of thyroiditis
Pregnancy, infection, autoimmune or drugs like amiodarone
Changes to deiodinase in illness
Conversion of T4 to T3 is impaired due to oxidative stress, altered redox state of cell and cytokine release so T3 levels also fall
Common causes of hypoT
Thyroiditis accounts for 90%- Hashimoto’s
Do thyroid hormones behave more like steroid hormones or peptide hormones
Steroid hormones
Four actions of thyroid hormone and pathogenic effects
Growth and development
Basal metabolic rate - hot and sweaty, rapid heart rate, bowels move too fast (diarrhea)
Thermogenesis in brown adipose tissue(feel hot)
Activate mental processes ( nervous and irritable, reduce concentration, slowed down thinking, low mood and depression)
How does free hormones fraction change in illness
Rises due to binding proteins like albumin being affected
How does illness affect TRH levels
Release from hypothalamus suppressed by cytokine (IL-1 and TNFa) and glucocorticoids like cortisol
how is fT4 in NTI
usually within reference range or moderately raised
How many Tyrosine rings in each hormone? What else is included
Catecholamines-1
Thyroid hormone- 2 + Iodine
How to differentiate TFTs in I’ll patients and patients with thyroid disease
Illness may increase fT4 and suppress TSH but will have low T3
Is glucose likely to be high or low in hyperT and why
Low due to increased metabolism of Cortisol in liver and increased metabolic demands which increases glucose uptake
Is TRAb high in thyroiditis
No
Is TSH high or low for all cases of hyperthyroidism
fT4
Low
High
Is tT3 or fT4 preferred for diagnosing Hyperthyroidism and why?
tT3 may be raised in patients with OCOP because of increased synthesis of thyroid binding globulin
Main cause of subclinical hypothyroidism
Autoimmune chronic thyroiditis
Main management of TED and additional measure
Manage in joint thyroid eye clinic
Achieve euthyroidism
Cease smoking
Topical lubricants for dry eyes
Selenium (200mcg daily as antioxidant)
Steroids for active eye disease
Add- rituximab and other additional immunosuppressants
Orbital dadiotherapy
Surgical decompression if raised intraocular pressure
Main signs of thyroiditis
Neck discomfort and prodromal flu symptoms
Past medical history to check in thyorid cases
Asthma- propranolol contraindicated
Rheart disease- risk of AF
Percentage of free T4
0.05%
Problems of I131
Need to avoid pregnancy for 6 months and restrict contact with children under 12 and pregnant women
Need to limit close contact with partner for 11 days
Risk of long term hypoT- higher for graves than TMNG or solitaryi nodule (80% for graves)
Risk of TED flaring up after treatment for Graves
Problems with hypothyroidism in pregnancy (overt Vs subclinical)
Infertility, miscarriage, pre-eclampsia, premature delivery, increased foetal mortality and impaired neurological development Vs neurodevelopmental delays and placental abruption
Risks of surgery for hyper T
Damage to recurrent laryngeal nerve and PT glands
May need thyroxine treatment
Symptoms and signs of hyperthyroidism
Weight loss despite very good appetite
Tiredness
Tremor
Hot and sweaty
Light or absent menses
Irritable or anxious
Eye disease (red, gritty, painful, double vision)
Muscle wasting
Symptoms of hypoT
Tired
Weight gain and puffy eyes and skin
Cold intolerance
Bradyc
Constipation
Dry hair and skin
Heavy periods
Hyperlipidemia
Goitre
Three kinds of thyroid binding proteins
Albumin 10%
Transthyretin 20%
Thyroid binding globulin 70%
Treatment for thyroiditis
Treatment with beta blockers but eventually commence thyroxine
Treatment of hypoT
Levothyroxine
Treatment regimen for graves
ATD first (12-18 months)
If recurrent use I131
Treatment regimen for TMNG
I1311 as no chance of long term remission with course of tablets
What amino acids are amines hormones derived from?
What do they make respectively
Tryptophan - Melatonin in Pineal Gland
Tyrosine- Catecholamines and thyroid hormones
What are the main treatments for hyper T
ATD like Carbimazole which blocks TPO
What can secondary hypo T be due to and what should be used to judge adequate replacement
Non functioning pituitary macroadenoma
fT4 levels to judge adequate replacements
What causes goitre in Graves
Due to trophic effects of TRABs
What conditions have TPO present
Graves
Underactive thyroid disease eg. Primary autoimmune thyroid failure
Autoimmune disease like Hashimoto’s
What drug can cause hypoT
Lithium
What enzyme is involved in the conversion of T4 to T3
Deiodinase enzyme
What examination sign is almost diagnostic of graves
Bruit over goitre- rushing noise heard with stethoscope due to increased vascular flow
What happens after colloid reabsorption
Proteolysis by lysosome to release T4
What happens to T3 on disease and why
T3 is reduced due to impaired T4 uptake in the liver and hence conversion of T4 to T3
What inhibits TSH release and what happens to TSH during illness
DA
Carbohydrate residues on TSH may be modified in NTI- affecting biological activity and plasma half life
What is the cause of high fT4 in thyroiditis
Due to damage from infection resulting in follicles spilling out
What is the recommended management of subclinical management
Treat is TSH> 10 on 2 occasions and/or TPOs are strongly positive
What is the treatment for papillary carcinomas
Total thyroidectomy and ablative dose of radioiodine and lifelong T4 replacement to prevent TSH from stimulating recalcitrant cancer cells
What medications impair T4 absorption
PPIs like Omeeprazole and lansoprazole
H2 antagonists like ranitidine
Iron, calcium and aluminium
All must take > 4 hrs before T4
What serum tumour marker for papillary carcinoma for thyroid
Thyroglobulin
What should be normalised in primary and secondary hypoT
Primary - normalise TSH
secondary - normalise fT4
When in gestation is maternal T4 used exclusively
Till 10/40, partially thereafter
When is T4/T3 needed for foetus and why
From 4-5/50 for development of CNS and growth and metabolism of foetus
When should surgery be considered for Hyper T
Patients with large goitre or eye disease or relapse of Graves r
When to increase dose of T4 for hypo G and why
if starting oestrogen or anticonvulsants
Antic speeds up breakdown of T4
Oestrogen increases level of Thyroid binding globulin
Where is T4 converted into T3
Liver, muscle and kidney
Why is heart rate increased in Hyperthyroidism
Due to increased B receptor activation
Why might there be dyspnoea in hyperthyroidism
Increased Co2 production by T4/T3
What happens to TSH levels in disease
Can be suppressed acutely but rises on recovery, may be misinterpreted as hypothyroidism
Should total or free thyroid hormone levels be measured in pregnancy and why
Free, as oestrogen increases synthesis of TBG
