Thyroid Gland and Its Disorders Flashcards
what is thyroid gland?
shape? lobes? joined by? location? other glands?
The thyroid gland is a butterfly shaped gland, in the neck over the trachea. It consists of a right and left lobe joined by a narrow isthmus.
There is also a variable pyramidal lobe. It weighs around 15-20 grams and there are parathyroid glands at the back.
what hormones are produced at thyroid gland?
T4 – thyroxine
T3 – Triiodothyronine
what controls hypothalamo-pituitary gland?
give the loop process
Endocrine organs, including the thyroid gland is under control of the hypothalamo-pituitary axis.
So, hypothalamus releases TRH, which stimulates the pituitary gland to release TSH, which stimulates the thyroid gland to synthesise and release T3/T4.
There can then be negative feedback of TH on pituitary gland
Give the two different broad thyroid problems
We have primary problem which is an issue with the gland itself and a secondary problem which is an issue with the pituitary.
Which hormone is released more and which is more active? where can hormones be converted? where else more specifically and why?
The thyroid gland mostly releases T4, but T3 is the much more active one.
Therefore, T4 may be converted to T3 in the liver but also specifically in target tissues (through the deiodinases), because your heart will need different amount of T3 compared to your CNS/brain etc.
what is thyroid gland made up of?
The thyroid gland is made up of thyroid follicles, which themselves are composed of a mass of colloid surrounded by follicular cells.
Follicular cells produce ?
Follicular cells produce thyroid hormone.
C-cells produce?
There are also para-folicular cells (C-cells), that produce calcitonin which are involved in calcium metabolism.
Colloid
Contains thyroglobulin which is a protein synthesised by the follicular cells.
Thyroglobulin contains tyrosine residues, which get combined with iodine which allow the formation of thyroid hormones.
3 different forms of thyroid hormone
T4: contains 4 iodines
T3: contains 3 iodines
Reverse T3: inactive
what is MIT and DIT
how are they formed?
Tyrosine + Iodine = monoiodotyrosine (MIT)
Monoiodotyrosine + iodine = diiodotyrosine (DIT)
• MIT + DIT = T3
• DIT + DIT = T4
how is most of the thyroid hormones transported in proprotion?
give names and % proportions
Over 99% of circulating thyroid hormones are bound to plasma proteins of which
- 70% is bound to thyroid binding globulin
- 10-15% bound to transthyretin
- 20-15% bound to albumin
Only a very tiny fraction is in the free form
Thyroid Disease
diffuse vs nodular?
what is goitre? difference between diffuse and nodular?
name for high and low levels of thyroid hormone
There is diffuse disease and nodular disease
Diffuse disease – whole gland
Nodular disease – local area
Englargement of the thyroid gland is called Goitre, if it is uniformly swollen it is called diffuse goitre. If it is lumpy, it is nodular goitre.
- Hyperthyroidism – Too much thyroid hormone, metabolism speeds up
- Hypothyroidism – Too little thyroid hormone, metabolism slows down
Hyperthyroidism
Symptoms/signs:
women?
elderly?
- Weight loss despite increased appetite
- Anxiety
- Palpatations
- Diarrhoea
- Hyperactivity -> need to be aware of this, as may be tricky for doctor
- Tremor
- Eye signs
- Tachycardia
- Exopthalamos (bulging eyes)
Note much more common in women, also note signs/symptoms are less prevalent/noticeable in the elderly.
Causes of thyrotoxicosis
what kind of disease is it commonly? two main diseases?
what will graves disease present? other eye signs?
Diagnosis of hyperthroidism? (3 things)
when is no additional testing required?
how can isotope uptake studies be used?
what two other things can be done?
Commonly it is autoimmune, in which case it would be Grave’s disease (80%) , or toxic multinodular goitre. (15%)
Uncommon causes are toxic adenoma or thyroiditis. Rare is TSH-oma or follicular thyroid cancer
In Graves Disease, someone will present with a smooth goitre and exopthalamos.
More eye signs include: • Periorbital oedema • Chemosis (swelling) • Lid retraction/lid lag • Proptosis (exophthalmos) • Opthalmoplegia (paralysis) Other features of Graves include: Diabetes, Vitilligo, Onycholysis, Dermopathy, Acropachy
Diagnosis of (primary) Hyperthyroidism is
- Suppressed TSH
- Elevated thyroid hormones
- In patients with overt opthalmopathy, no additional testing is required for the diagnosis
Isotope uptake studies can be used -> nuclear medicine test and scan, to see where uptake is in the thyroid.
Thyroid USS (ultrasound)
TSHr Antibody levels -> the antibody in Graves in blood
Treatment Under a Specialist
name a few antithyroid medication and what they do?
Why are beta blockers used?
Other treatment
what is thyroid storm?
Antithyroid medications can be used including Carbimazole, Methimazole and Propylthiouracil block TPO (thyroid perioxidase) enzyme.
Beta blockers will help patients feel better, as the effects of high thyroid are like there is high adrenaline, note it is not the treatment but temporary relief while other medications work.
You can use radioactive iodine as well as surgery
Thyroid Storm is an extreme form of thyrotoxicosis and occurs with stressful illness or thyroid surgery. It is manifested by marked delirium, severe tachycardia, vomiting, diarrhoea, dehydration and very high fever. Mortality rate is high in this state.
Hypothyroidism
how is primary and secondary distinguished?
clinical features?
Hypothyroidism is very common, there is then the distinction between primary (caused by underfunction of thyroid gland itself) or secondary (due to pituitary gland underfunctioning).
Clinical Features • Fatigue • Cold intolerance • Weight gain • Bradycardia • Constipation
Hashimoto’s Disease
primary or secondary?
what is the pathology and why doesnt the amount of idoine you take matter?
who is it more common in?
o Hashimotos disease is the most common cause of hypothyroidism in iodine sufficient areas and is due to antibodies again directed towards TPO or thyroglobulin.
o It is also much more common in females. Hashimoto’s is a form of primary hypothyroidism.
other reasons for hypothyroidism
Other causes of hypothyroidism are post-thyroidectomy (someone had an overactive thyroid and you removed it) or post RAI (radioactive iodine, destroys it).
There is also iodine deficiency or iodine excess, as well as certain drugs and secondary hypothyroidism.
investigations for hypothyroidism
oWe would note low free T4 and high TSH (if primary)
oCould test TPO antibody levels
Treatment for for hypothyroidism
what drug is given?
if drug doesnt work, what could this mean?
Treatment is often managed by the GP, by giving them the missing hormone in the form of levothyroxine.
Remember that patients still can develop other autoimmune conditions (e.g. Addison’s, if you put a person on thyroxine and they feel worse, it is likely they have Addison’s disease)
Severe Hypothyroidism
What is myxedema? what is it the opposite of? what could cause it?
symtoms?
Does blood thyroid level matter?
The opposite of thyroid storm is myxedema. Could be caused by long-standing untreated hypothyroidism, precipitated by infection, myocardial infarction, cold exposure or sedative drugs.
Mortality rate is 20-25%
- Results in decreased mental status, hypothermia and other symptoms related to slowing of function in multiple organs.
Note that the magnitude of TSH elevation or free T4 do not correlate well with the severity of clinical presentation, i.e. numbers alone do not tell us about the patient’s condition.
Thyroiditis
4 different types
o Hashimotos thyroiditis -> painless, diffuse goiter
o Post-partum thyroiditis (after delivery of baby)
o Subacute thyroiditis -> Anyone can get, painful thyroiditis
o Acute thyroiditis -> Bacteria, fungus etc.
Goitre Presentations
3 symptoms the size of the goitre may result in
3 different types of goitre classification
There are different types of goitre classifications:
o Euthyroidism = Normal thyroid function (Eurothyroid goitre) o Hypothyroidism (hypothyroid goitre) o Hyperthyroidism (Hyperthyroid goitre)
Size of goitre may result in
- Dysphagia = difficulty swallowing
- Dysphonia = Inability to produce sounds
- Dyspnoea = Breathless
Thyroid Tumours
5 different thyroid cancers?
Investigations after somoneone come in with thyroid lump ( 4 things)
Below are types of thyroid cancer
- Papillary Thyroid carcinoma
- Follicular carcinoma
- Anaplastic carcinoma (worst prognosis)
- Medullary thyroid carcinoma
- Lymphoma
Investigations
So, someone comes into clinic with thyroid lump
- Find out symptoms match hyper or hypo
- Decide if diffuse or nodular goitre
- Do thyroid blood test, are they eu-,hypo-hyper- thyroid?
- FNA (fine needle aspiration) cytology, to have a look at it and take a few cells to look at under a microscope
Serum assays
FT4 High
fT3 High
TSH Suppressed
Primary hyperthyroidism – most likely cause is graves disease
Serum assays
FT4 High
fT3 High
TSH High
Secondary hyperthyroidism.
We scan pitutiary gland
Serum assays
FT4 Low
fT3 Low
TSH High
Primary hypothyroidism
Serum assays
FT4 Low
fT3 Low
TSH Low
Secondary hypothyrodism
Typical Thyroid Hormone Levels in Thyroid Disease
Hypothyroidism
TSH - high
T4 - low
T3 - low
hyperthyroidsim
TSH - low
T4 - high
T3 - high
