🧪Endocrinology🧪- Hyperthyroidism Flashcards
Outline the hypothalamic-pituitary thyroid axis
What level of TSH will you find in a patient with primary hypothyroidism, where the thyroid gland has been destroyed by the immune system?
High TSH
Outline Graves’ disease
Autoimmune
Antibodies bind to and stimulate TSH receptors in the thyroid
Causes (smooth) goitre and hyperthyroidism
What are the key features of Graves’?
What are the 2 most key features of Graves’, completely specific to Graves’?
Exophthalmos
Pretibial myxoedema
How do exophthalmos and pretibial myxoedema arise in hyperthyroidism?
Other antibodies bind to muscles behind the eye and cause exophthalmos
Other antibodies cause pretibial myxoedema (hypertrophy)
What is pretibial myxoedema?
The swelling (non-pitting) that occurs on the shins of patients with Graves’ disease: growth of soft tissue
Not to be confused with myxoedema=hypothyroidism
How can Graves’ be diagnosed?
TSH-receptor antibody (TRAb) (against the TSH receptor)
Measured in the bloodstream, positive in Graves’ disease
First-line investigation to confirm Graves’ disease
What would a radioiodine scan of a thyroid look like in Graves’
Outline toxic nodular thyroid disease, and how is immediately symptomatically distinguishable from Graves’?
Single toxic nodule/multiple toxic nodules (multinodular goitre)
NOT autoimmune
Benign adenoma(s) overactive at making thyroxine.
NO pretibial myxoedema
NO exophthalmos
How would toxic nodular thyroid disease appear?
What effects does thyroxine have on the sympathetic nervous system?
Sensitises beta-adrenoceptors to ambient levels of adrenaline and noradrenaline
Therefore, there is apparent sympathetic activation
Leads to tachycardia, palpitations, tremor, lid lag
What are the features of hyperthyroidism?
Weight loss despite increased appetite
Breathlessness
Palpitations, tachycardia
Sweating
Heat intolerance
Diarrhoea
Lid lag and other sympathetic features
What is a thyroid storm?
Thyroid gland releases a large amount of thyroid hormone in a short amount of time
Why are thyroid storms so serious?
Medical emergency: untreated has 50% mortality
What would someone experiencing a thyroid storm present with?
Hyperpyrexia > 41oC
Accelerated tachycardia / arrhythmia
Cardiac failure
Delirium / frank psychosis
Hepatocellular dysfunction; jaundice
Needs aggressive treatment
What are the treatment options for hyperthyroidism?
Drugs
Surgery
Radioiodine
What classes of drugs are used in the treatment of hyperthyroidism?
Thionamides (anti-thyroid drugs, propylthiouracil, carbimazole)
Potassium Iodide
Radioiodine
beta-blockers
How are beta-blockers different from other drugs used to treat hyperthyroidism?
Other drugs reduced thyroid hormone synthesis
Beta-blockers just manage symptoms
How are thionamides used?
Daily treatment of hyperthyroid conditions
What is the mechanism of action of thionamides?
Inhibits thyroid peroxidase, so stopping activation of iodide ions and so production of MIT/DIT and thus thyroid hormones
How long does it take for thionamides to take effect?
Biochemical effect occurs within hours
Clinical effect takes weeks
Why does it take weeks for thionamides to have a clinical effect?
It only stops synthesis of new thyroid hormones - existing stores remain
Only once existing stores are depleted will the clinical effects be seen
What are the unwanted actions of thionamides?
Agranulocytosis (usually reduction in neutrophils) - rare and reversible upon withdrawal of drug
Rashes - relatively common
What is the follow up for hyperthyroid treatment?
Usually aim to stop anti-thyroid drug treatment after 18 months
Review patient periodically including thyroid function tests for remission/relapse
How are beta-blockers used in thyrotoxicosis?
Takes several weeks for ATDs to have clinical effects
Non selective bet blockers - propranolol
Achieves clinical effects in the interim
What is iodide (usually KI) ‘s role in thyrotoxicosis management?
Preparation of hyperthyroid patients for surgery
Severe thyrotoxic crisis (thyroid storm)
Not used in patients opting for long-term medical treatment of Graves’
What is the mechanism of action of KI?
Induces the Wolff-Chaikoff effect (excess iodide levels in thyroid inhibits thyroid hormone synthesis)
Hyperthyroid symptoms reduce within 1-2 days
Vascularity/size of gland reduces within 10-14 days
Why does Thiouracil lead to thyroid swelling?
Inhibition of T3/T4 synthesis leads to increased TSH levels
TSH stimulates thyroid growth
What are the risks associated with thyroid surgery?
Risk of voice change (recurrent laryngeal nerve)
Risk of also losing parathyroid glands
Scar
Anaesthetic
How is radioiodine taken?
Swallow a capsule containing about 370 MBq (10 mCi) of the isotope I (131)
Contraindicated in pregnancy
Need to avoid children and pregnant mums for a few days
Briefly outline the pharmacological treatment options for hyperthyroidism?
Beta-blockers:
-Beta blockade is VERY IMPORTANT
-propranolol
Anti thyroid drugs :
-Carbimazole
-Propylthiouracil
Radioiodine
What are the signs//symptoms of viral thyroiditis?
Painful dysphagia
Hyperthyroidism
Pyrexia
Thyroid inflammation
What is the mechanism of viral thyroiditis?
Virus attacks thyroid gland causing pain and tenderness
Thyroid stops making thyroxine and makes viruses instead
Thus no iodine uptake (ZERO)
How would a thyroid scan of Graves’ compare to that of viral thyroiditis?
What is the classic progression of viral thyroiditis?
Radioiodine uptake zero
Stored thyroxine released in large quantities - hyperthyroidism
Thus toxic with zero uptake
Four weeks later, stored thyroxine exhausted, so hypothyroid
After a further month, resolution occurs (like in all viral diseases).
Patient then becomes euthyroid again.
Briefly summarise pattern of thyroid activity in someone with viral thyroiditis
Patient exhibits viral thyroditis symptoms, becomes hyperthyroid
4 weeks later, thyroid hormone exhausted, so becomes hypothyroid
After a further month, resolves (like in most viral diseases), patient becomes euthyroid
What other condition mimics the pattern of hyper- then hypo- thyroidism exhibited by viral thyroiditis?
Postpartum thyroiditis
Why does postpartum thyroiditis occur?
Immune system modulated during pregnancy
After birth, immune bounce back can lead to autoimmune attack on thyroid
What is the main difference between postpartum thyroiditis and viral thyroiditis?
Postpartum thyroiditis similar but no pain and only occurs after pregnancy
