MEH - Thyroid Flashcards
Can you feel a normal sized thyroid on examination?
No
What is the pre-tracheal facia? Why is this relevant in diagnostics?
It attached the thyroid gland to the trachea and larynx, and so the thyroid moves up with swallowing. This is important when looking at lumps in the neck and where they originate from.
How else can you examine the thyroid other than palpation (2)?
Ultrasound is commonly used
Iodine scen - thyroid takes up iodine dye - can show enlarged lobes
Is the thyroid gland the first gland to develop in foetus?
Yes
When in foetal development does the thyroid develop and from what structure?
4-7weeks - from tongue - proliferation of epithelial cells.
What is a lingual thyroid?
An ectopic thyroid that has failed to migrate downwards during normal embryonic development - can see it when people open their mouths
What is the thyroglossal duct and what is a thyroglossal duct cyst? Where anatomically on the neck is this seen?
It is an embryological structure that allow the thyroid to migrate caudally during development, usually disappears, but remnants may remain and form a thyroglossal duct cyst. Seen within the body of the hyoid and is always at the front in the midline of the neck
Where does a thyroglossal cyst move to on tongue protrusion?
Moves upwards because of its attachment to the tongue
Define a cyst?
A fluid filled bag
What is metabolic thyroid disease used to describe? Does the abnormality most commonly come from the thyroid gland itself or the pituitary gland?
Over or underachieve thyroid
98% from thyroid gland itself
Rarely from pituitary gland - either benign adenoma releasing TSH, or pituitary failure causing hypothyroidism
What is thyrotoxicosis used to describe?
The main cause of thyrotoxicosis is hyperthyroidism
What would you measure to screen for hyper or hypothyroidism? Would it be high or low for both? Would free T4 levels be high or low for hypo and hyperthyroidism?
TSH levels
High = underactive
Low = overactive
Free T4
Low - underactive
High - overactive
Why are the ranges for normal TSH and T4 so wide?
Because there is a wide range of normal concentrations due to homeostasis responding to environment - temp/light/ etc.
Do autoimmune disease commonly affect endocrine glands? Give examples
Yes
E.g. pancreas Islets of Langerhans - T1 diabetes
Thyroid - Graves/Hashimotos
Adrenal - Addisons
Are autoimmune conditions more common in men or women?
Women
What does a goitre mean? What three types? Are they more common in men or women - do we know why?
A thyroid swelling can be single nodule, multi nodular, or diffuse.
More common in women 7% vs 1% male - maybe something to do with oestrogen/progesterone ratio
When might you get a physiological goitre (3)? Is thyroid function normal or not here?
Menarche - first menstrual cycle
Pregnancy
Menopause
Normal thyroid function
What is the most common cause of goitre globally compared to UK?
Globally - iodine deficiency
UK - multinodular - usually normal thyroid function
What happens with iodine deficiency causing a goitre?
Reduced thyroxin leads to overproduction of TSH - leads to thyroid enlargement - usually nodular. Can lead to hypothyroidism - really common esp in mountainous areas
What causes a multi nodular goitre?
Unknown cause - common un UK. More common in women. A small number go on to develop hyperthyroidism - toxic multinodular goitre.
What can happen to the foetus if iodine deficiency occurs in pregnancy?
If the mother is iodine deficient the foetus is too. Leads to mental retardation, short stature, abnormal gait, deaf-mutism, goitre, hypothyroidism.
How can a goitre cause tracheal compression and what might the symptom be?
If a multinodular goitre enlarges inferiorly into the superior mediastinum then it may compress the trachea - may cause inspiratory stridor due to the retrosternal goitre.
What general metabolic/menstrual/mental health symptoms arise from hypothyroidism (name a few). What is the typical facial colouring you may see?
Weight gain Lethargy Menorrhagia Cold intolerance Hairloss - particularly outer third of eyebrows Constipation If really bad - myxoedema Psychosis if severe
May see ‘peaches and cream’ pallor
What is myxoedema and how does it occur? What is it also used to describe?
Non-pitting oedema, especially in the face, hands, feet. Due to deposition of mucopolysaccharides (Glycosaminoglycans (GAGS)).
Also used to describe hypothyroidism in general
Name 3 causes of hypothyroidism
Hashimoto’s disease (autoimmune)
Iodine deficiency
Thyroidectomy
What occurs in Hashimoto’s disease? What happens to the size of the thyroid?
Autoimmune destruction of the thyroid
Antibodies to thyroglobulin and thyroid peroxidase in the blood
May or may not initially increase in size - goitre due to inflammation
Eventually shrinks in size due to destruction
How do you treat hypothyroidism? Can you give it orally?
Oral Thyroxine - not destroyed by gastric acid
What is hyperthyroidism?
Thyrotoxicosis caused by increased thyroxine by the thyroid gland
What are some general metabolic/menstrual symptoms of hyperthyroidism?
Overactivity/nevousness/anxious/insomnia Shaking etc Warm Sweaty hands Amenorrhea Heat intolerance
What CVS symptoms might you see with hyperthyroidism?
Palpitations/tachy
Bounding pulse - due to wide pulse pressure
What is a lid lag? Why might you see this and staring eyes in hyperthyroidism?
You may also see lid-lag where the patient’s eye lids don’t follow down straight away.
Because the eye muscle is 10% smooth muscle which is under sympathetic innervation, and overstimulation of this causes the eye bulge and lid-lag.
3 causes of thyrotoxicosis due to hyperthyroidism? Which is most common, and least
Graves disease - most common
Toxic multi nodular goitre - 2nd
Toxic adenoma of the thyroid gland - least common
What is the name of the immunoglobin that circulates in Grave’s disease? What does it do?
Thyroid stimulating immunologlobulin (TSI). It attaches and stimulates the TSH receptor causing thyrotoxicosis
What else does Graves disease have? Whats exophthalmos? Can exophthalmos occur in Graves disease without thyroid dysfunction?
Exophthalmos (bulging eyes)
Pre-Tibial myxoedema (nothing to do with myxoedema in hypothyroidism don’t get confused).
Yes may occur in Grave’s without thyroid dysfunction
With a toxic multi nodular goitre do you get the same features as graves disease hyperthyroidism? Why?
No - don’t get myxoedema or exopthalmos as it’s not autoimmune.
How do you treat thyrotoxicosis (3) and what’s the drugs mechanism of action?
Carbimazole - inhibits thyroid peroxidase from coupling and iodinating thyroglobulin so reduced T4 made.
Thyroidectomy
Radio-ablation with iodine
Are thyroid cancers common? Do they cause metabolic thyroid disease? Is prognosis good for thyroid cancer?
Thyroid cancers are rare
Only 1% of thyroid nodules are malignant
Thyroid cancers do not cause metabolic thyroid dysfunction
Yes prognosis is excellent 97%
Which three conditions may you have a goitre but no thyroid dysfunction?
Multinodular goitre
Iodine deficiency
Thyroid cancer
What are the basic steps of synthesis of T3 and T4?
In thyroid follicles
Transport of iodide into the epithelial cells against a concentration gradient
Synthesis of tyrosine rich protein (thyroglobulin) in the epithelial cells
Secretion (exocytosis) of thyroglobulin into the lumen of the follicle
Oxidation of iodide to produce iodine
Iodination of tyrosine side chains
Coupling of DITs and MITs to form T3 and T4 respectively
How many iodines do T3 and T4 have attached?
T3 - 3
T4 - 4
What ratio of T3:T4 is made?
1:10
Where are T3 and T4 stored?
In the lumen of the follicles as part of thyroglobulin molecules - in colloid
How long does T3 and T4 storage last?
Several months
How is T3 T4 released from thyroglobulin in colloid when needed?
Endocytosis back into follicular cells - then proteolytic cleavage of thyroglobulin releases T3 T4 and these diffuse from epithelial cells into the circulation
What is the hypothalamic hormone released to control thyroid hormone release?
Thyrotropin releasing hormone
What does TRH stimulated release of and from where?
TSH from anterior pituitary
How does TSH stimulate T3 T4 release?
Receptors on surface of follicular cells that stimulates all aspects of T3 and T4 production and secretion
What effect can TSH have on the size of the thyroid?
Can cause increased size and number of follicular cells which can lead to a goitre +/- hyperthyroidism
Which has the shorter half life T3 or T4?
T3 due to lower binding affinity for thyroxine binding globulin
What are the effects of T3 T4 on the body (9)?
General metabolic activity of all tissues - increases
Increases glucose uptake and metabolism
Stimulates mobilisation and oxidation of fatty acids and stimulates protein metabolism
Increase BMR, heat production and O2 consumption
Important for normal growth and development - indirectly via metabolism but also specific effect on bone mineralisation and physical growth and synthesis heart muscle protein.
What can the absence of T3 T4 lead to in children up to adolescence?
Cretinism
Which is the more active form T3 or T4?
T3 10 times more active use to the greater affinity of the THR for T3 in the nucleus of cells
What do the parafollicular cells (C cells) of the thyroid secrete?
Calcitonin
Is most of Thyroxine secreted as T3 or T4?
90% T4 but T3 actually more biologically active - gets converted
Which has the longer half-life T3 or T4?
T4
