Hyperthyroidism Flashcards
Which cells respond to TSH?
Follicular cells of the thyroid gland
Which endocrine cells release TSH?
Thyrotrophs within the anterior pituitary gland
How is iodine pumped into follicular cell of the thyroid gland?
Sodium-iodine symporter, using secondary active transport.
How is iodide pumped from the follicle into the colloid?
Pendrin pumps within the apical membrane
Which thyroglobulin residues are iodinated?
Tyrosine residues
Which thyroid pro-hormone is iodinated?
Thyroglobulin
How is iodine activated into iodide?
Under the action of thyroid peroxidase in the presence of hydrogen peroxide.
Where does iodination occur within the thyroid gland?
Within the colloid
What are the two direct products of iodination of thyroglobulin within the colloid?
MIT and DIT
How is triiodothyronine formed?
Coupling of MIT and DIT
How is tetraiodothyronine formed?
Coupling of DIT molecules
Which thyroid hormone is active?
T3
Which structures are directly inhibited by thyroxine via negative feedback mechanisms?
Anterior pituitary gland (thyrotrophs) Hypothalamic neurones (secreting TRH)
What level of TSH will you find in a patient with primary hypothyroidism where the thyroid gland has been destroyed by the immune system?
There is an elevated TSH, considering thyroxine secretion from the thyroid gland is reduced. Thus through negative feedback mechanisms, TSH is elevated as a compromise.
Which drug is prescribed in patients with hypothyroidism?
Levothyroxine
How should levothyroxine be administered?
Levothyroxine is administered as oral preparations to patients, the dose is increases until the TSH levels are normal.
Which effect demonstrates the auto-regulatory function of iodine control?
Wolff-Chaikoff effect
What is the Wolff-Chaikoff effect?
The Wolff-Chaikoff effect demonstrates an autoregulatory function, whereby an excess ingestion of iodine inhibits thyroid peroxidase activity and thus reducing iodothyronine production within thyroid follicular cells, independent from the serum-level of thyroid-stimulating hormone (TSH).
What is the pathophysiology of Grave’s disease?
TSH Immunoglobulins binds to TSH receptors in the thyroid gland.
-Stimulation of TSH receptors subsequently result in smooth goitre formation and hyperthyroidism.
What are the clinical features of Grave’s disease?
Respiration, facial flushing Muscle wasting Shortness of breath Heat intolerance Weight loss - despite increased appetite Localised myxoedema Tremor Sweating Palpitations Exophthalmos (proptosis)
What is pretibial myxoedema?
The swelling that occurs on the shins of patients with Grave’s disease: growth of soft tissue
What type of goitre is shown in a patient with Plummer’s disease?
Toxic nodular goitre
Benign nodules of the thyroid gland (not autoimmune associated)
What type thyroid scan is conducted to identify the type of goitre?
Iodine-123 scan
Which part of the thyroid gland uptakes iodine-123 in Plummer’s disease?
The toxic nodular goitre. The inactive thyroid gland is suppressed due to the adenoma.
What is the effect of thyroxine on the heart rate?
Sensitives beta adrenoreceptors to ambient levels of adrenaline and noradrenaline.
This increases the heart rate ( tachycardia and tremor in hands)
-lid lag
What are the main clinical features of a thyroid storm?
Hyperpyrexia > 41 Accelerated tachycardia/arrhythmia Cardiac failure delirium/frank psychosis Hepatocellular dysfunction; jaundice
What are the main treatment options for a thyroid storm?
Thyroidectomy
Radioiodine
Drugs
What class of drug is the main anti-thyroid?
Thionamides
- Propylthiouracil (PTU)
- Carbimazole (CBZ)
What are the four main classes of drugs used in the treatment of hyperthyroidism?
1) Thionamides
2) Potassium Iodide
3) Radioiodine
4) Beta-blockers
What purpose do beta-blockers have in terms of hyperthyroidism treatment?
Alleviate the symptoms concerned with arrhythmia.
Which enzyme is inhibited by thionamides?
Thyroid peroxidase
What is the mechanism of action of thionamides?
Inhibition of thyroid peroxidase and peroxidase transaminase, therefore reduce iodine activation and iodination of thyroglobulin into MIT & DIT.
Why does it take 3-4 weeks for the clinical effects of anti-thyroid hormones to become apparrent?
There is a months store of thyroxine
Which co-drug is prescribed alongside thionamides?
Propanolol rapidly reduces tremors and tachycardia.
What are the unwanted actions of thinamides?
Agranulocytosis (reduction in neutrophils) - neutropenia increases risk of sepsis.
-Rashes (common)
How long should anti-thyroid drugs typically be prescribed for?
18 months
What is the role performed by beta blockers in thyrotoxicosis?
Reduces heart rate and beta adrenoreceptor sensitivity
Which drug should be pre-operatively administered in hyperthyroid patients?
Potassium Iodide - induces Wolff-Chaikoff effect (10 days)
What effect does KI have in hyperthyroid patients?
Inhibits hydrogen peroxide generation and thyroid peroxidase.
Reduces vascularity and size of gland (atrophy of thyroid gland)
Inhibits the iodination of thyroglobulin by inducing the Wolff-Chaikoff effect
Which nerve is at risk of damage during a thyroidectomy?
The recurrent laryngeal nerve
What are the associated risks with a thyroidectomy?
1) Risk of voice change
2) Risk of also losing parathyroid glands
3) Scar
4) Anaesthetic
Which isotope is used in radioiodine?
Iodine 131
Emits radiation for 10 days therefore avoid pregnant individuals
Which radioisotope is administered for a thyroid scan?
Tc-99
What are the four main features of viral thyroiditis?
Painful dysphagia
Hyperthyroidism (The thyroid gland is tender and palpable)
Pyrexia (fever)
Thyroid inflammation
Describe the pattern of iodine uptake in an individual with viral thyroiditis?
There is no iodine uptake as the thyroid gland stops making thyroxine.
How is hyperthyroidism induced in individuals with viral thyroiditis?
Round follicle is damaged, subsequently causing stored thyroxine within the colloid to be released
How is hypothyroid caused in individuals with viral thyroiditis?
Four weeks upon the onset of viral thyroiditis, stored thyroxine is depleted.
