7. Thyroid Disease - Hyperthyroidism Flashcards
What would you expect the TFT to show in someone with hyperthyroidism
low TSH
high T3 and T4
what would you expect the TFT to show in someone with primary hypothyroidism
high TSH
low T3 and T4
what would you expect the TFT to show in someone with secondary hypothyroidism
low TSH
low T3 and T4
What antibodies are usually present in graves disease and hashimotos thyroiditis
antithyroid peroxide (anti-TPO) antibodies (against the thyroid gland itself) in hashitmotos Antithyroglobulin antibodies - TSH receptor antibodies in graves disease
what is graves disease
autoimmune condition where TSH receptor antibodies cause primary hyperthyroidism
these are abnormal antibodies produced by the immune system and mimic TSH
In a radioisotope scan to investigate hyperthyroidism and thyroid cancers what conditions give the characteristic clinical finding
- diffuse high uptake of the isotope
- focal high uptake of the isotope
- ‘cold’ areas (ie abnormally low uptake) of the isotope
- graves disease
- toxic multinodular goitre and adenomas
- thyroid cancer
define Hyperthyroidism and what is it also known as
over production of the thyroid hormone by the thyroid gland
aka thyrotoxicity
What is the difference between primary and secondary hyperthyroidism
primary is due to thyroid pathology (the thyroid itself is behaving abnormally)
secondary is as a result of overstimulation by TSH and the pathology is in the hypothalamus or pituitary
what is the most common cause of hyperthyroidism
Graves disease
what is toxic multi nodular goitre (aka plummers disease )
nodules develop on the thyroid gland that act independently of the normal feedback system and continuously produce excessive thyroid hormone
What is exophthalmos
bulging of the eyeball out of the socket caused by graves disease. Due to inflammation, swelling and hypertrophy
what is pre-tibial myxoedema
deposits of mucin under the skin on the anterior aspect of the leg
specific to graves disease and is a reaction to the TSH receptor antibodies
Describe where the thyroid gland is located and the basic structure
- soft gland in the lower neck, anterior to the trachea, below the thyroid cartilage of the larynx, moves when you swallow
- makes thyroxine (T4) and T3 and is composed of 2 lobes and an isthmus
What other conditions could present with weight loss and what questions would you ask
- GI symptoms: anorexia, abdo pain, diarrhoea, symptoms of IBD, coeliac disease, peptic ulcer
- Symptoms of depression: low mood, loss of interest, sleep disturbances
- Symptoms of eating disorder: decreased food intake, self-induced vomiting, over exercise. Anorexia nervosa and bulimia may commonly present in this age group (early 20s)
- Polyuria and polydipsia: type 1 diabetes mellitus may present with weight loss
- Drug use: including alcohol, cocaine, amphetamines, cannabis
- Night sweats or fevers: although malignancy is rare in this age group, lymphomas may present with weight loss. TB and HIV can also present this way
Describe the basic histology of the thyroid gland
- Made up of follicles lines by cuboidal epithelium and parafollicular C cells that secrete calcitonin
- follicles are filled with colloid (looks pink)
- follicular cells make thyroglobulin
what are c cells involved in
the production of calcitonin involved in bone mineral deposition
what are adjacent to thyroid gland
parathyroid glands
Describe the basics of T3 and T4 production
- they are thyroninies that are made from thyroglobulin
- TFC make thyroglobulin under the control of TSH
- Iodine is trapped by TFC and transported into the colloid
- thyroid peroxidase in the follicular cells (TFC) iodinates tyrosine
- thyroglobulin hydrolysed and T4 is released into the blood by thyroid binding globulins
- T4 deiodinated into T3 which is more active and binds to DNA (transcriptional effects)
- T3 is 10X more active than T4
What is the overall effect of T3
increased metabolic rate 8
Describe the pituitary-thyroid hormone axis
- negative feedback of T4/T3 on pituitary TSH and hypothalamic TRH
- Low T4 –> increased TSH
- high T4 –> suppressed TSH
- TSH released from anterior pituitary
In clinical practice we measure the free T4 so not that significant but what things will raise the thyroid binding globulin, increasing TBG-T4
pregnancy and OCP
Name some common drugs that can affect hormone levels
Amiodarone (anti-arrhythmic medication)
Lithium (anti-psychotic)
Interferon (hep C treatment)
What are the top 3/4 common causes of thyrotoxicosis
Graves disease
multi nodular goitre
solitary toxic nodule (solitary benign adenoma)
Drugs such as interferon (hep C treatment) and amiodarone ( anti-arrhythmic)
{thyroiditis in the very early stages cause this usually causes hypothyroidism)
what are the cardiovascular effects of thyrotoxicosis
Higher pulse and BP
Can get atrial fibrillation and this is a 3X risk in the over 60s
What are the universal features of hyperthyroidism
anxiety and irritability sweating and heat intolerance tachycardia (palpitations; AF) weight loss (despite good appetite) fatigue frequent loose stools sexual dysfunction
Graves disease features (see next question)
what are the unique features of graves disease
Diffuse Goitre (without nodules) Graves eye disease - chemosis (swelling of the conjunctiva) - peri-orbital odema bilateral exophthalmos (aka proptosis) pretibial myxoedema
What features are unique of toxic multi nodular goitre
goitre with firm nodules
most patients are aged over 50
second most common cause of thyrotoxicity (after graves)
what is a solitary toxic thyroid nodule
single abnormal nodule is acting along to release thyroid hormone
nodules are usually benign adenomas
treated with surgical removal
what is De Quervain’s thyroiditis
viral infection with fever, neck pain and tenderness, dysphagia and features of hyperthyroidism
- there is a hyperthyroid phase followed by hypothyroid phase (due to negative feedback)
- self limiting condition and supportive treatment with NSAID and beta blockers is all that is needed
What is thyroid storm
this is rare presentation of hyperthyroidism that is a thyrotoxic crisis
- pyrexia, tachycardia and delirium
- requires admission for monitoring
- may need supportive care with fluid resuscitation, anti-arrhythmic medication and beta blockers
What are the main treatments for hyperthyroidism
Carbimazole 1st line (CBZ) - once a day Propylthiouracil 2nd line (PTU)- 3 times a day Radioactive iodine Beta-blockers Surgery
Why is Carbimazole preferred over Propylthiouracil
There is a small risk of severe hepatic reactions, including death, with PTU
what is the difference between ‘titration-block’ and ‘block and replace’ when treating with Carbimazole
titration-block is where you carefully titirate to maintain normal levels
block and replace is where the dose is enough to block all production and the patient takes levothyroxine titrated to effect
What are the strict rules that must be followed when taking radioactive iodine
must not be pregnant and can’t get pregnant within 6 months of having it
must avoid close contact with children and pregnant women for around 3 weeks (dose dependant)
limit contact with anyone for several days after receiving the dose
why might beta-blockers be given in patents with hyperthyroidism
- to block he adrenaline related symptoms
- propranolol is a good choice as it is non-selective
- don’t treat the underlying problem but control the symptoms whist the treatment has time to work
when titrating the initial dose of 40 mg of CBZ what should the subsequent doses go down in
5-10 mg decrements for 18-24 months
in the block replace method using CBZ, at what point do you stop the 40mg dose and switch to levothyroxine and at what dose
100 mcg when T4 levels are normal and then this dose can be adjusted
(note that cannot be pregnant whilst doing this)
What is the main reg flag issue with using anti-thyroid drugs and what do you need to explain to the patient
- neutropenia and agranuulocytosis which is when you stop making neutrophils
- need to give patients written warning advise which includes that the patient needs to report signs of infection, especially a sore throat
- if this occurs then anti-thyroid drug should be stopped and antibiotics should be given in hospital
myth busted: dose radioactive iodine treatment cause cancer or infertility
no doesn’t cause infertility but there is a risk of radiation so say not to become pregnant till 6 months after treatment
there is no excessive risk of developing thyroid cancer either
what are the main complications with radioactive iodine
can get neck discomfort and can precipitate graves ophthalmopathy
what are the main risks with a subtotal or near-total thyroidectomy
may get permanent parathyroid damage 2-4% vocal cord paralysis less than 1% bleeding less than 2% keloid scar hypothyroidism is inevitable
what can cross the placenta and stimulate tithe thyroid gland of the foetus
thyroid stimulating antibodies in graves disease
