Hyperthyroidism Flashcards
2 common causes
Grave’s disease (autoimmune)
Plummer’s disease (not autoimmune)
What happens in Grave’s disease
Antibodies bind to TSH receptor in thyroid
Makes thyroid overactive
Clinical features of hyperthyroidism
Lid lag Tachycardia Palpitations Weight loss and increased appetite Sweating Heat intolerance Breathless Diarrhoe
How to differentiate between Graves and other causes of hyperthyroidism
Graves - antibodies bind to receptors behind eye, in soft tissue of shin etc. Get: exophthalmos pretibial myxoedema goitre (smooth enlarged thyroid)
Plummer’s disease is caused by
Toxic nodular goitre
Benign adenoma –> overactive –> makes thyroxine
Plummer’s disease CF
same as Grave’s –> losing weight, increased appetite, hot, tachycardia, palpitations, breathless etc
But
Lump is on one side (tumour only on one side of the thyroid)
What scan can you do
Technitium/iodine scan
Iodine scan will show the iodine going to the tumour
Plummer’s: there’s too much thyroxine from the tumour part of the thyroid gland–> pituitary stops making TSH–> normal part of gland stops making thyroxine and shrinks
On scan, Plummers: one hot nodule
Graves: large smooth thyroid gland
What is a rare but severe complication of hyperthyroidism
mortality if untreated. Die of..
thyroid storm
50%
Heart failure or arrhythmia
Clinical features of thyroid storm
Hyperpyrexia (temp >41) tachycardia/ arrhythmia cardiac failure delirium/ frank psychosis hepatocellular dysfunction - jaundice
Treatment options for thyroid storm
Surgery - thyroidectomy
Radioiodine
Drugs
Cause/ what happens in viral thyroiditis
Virus attacks the thyroid so it stops making thyroxine and makes the virus itself. Causes fever
Damage the thyroid follicles so all the stored thyroxine is released.
Symptoms/ CF of viral thyroiditis
Painful dysphasia
Pyrexia
Hyperthyroidism
Raised ESR
Patient with viral thyroiditis presents with
hyperthyroidism - overactive thyroid - as all the stored thyroxine is released
If you do a technetium scan on a patient with viral thyroiditis what do you see and why
See no radioiodine uptake because the thyroid stopped making thyroxine
What happens a month after a patient has had viral thyroiditis
And a month after that?
They become hypothyroid as all the stored thyroxine is exhausted.
The cells are recovered and start producing thyroxine again - patient becomes euthyroid again
Treatment for hyperthyroidism
Drugs that decrease thyroid hormone synthesis (anti-thyroids)
- Thionamides e.g. Propylthiouracil (PTU); Carbimazole (CBZ)
- Potassium iodide
- Radioiodine
Drugs that help with the symptoms
- beta blockers
Thionamides can be used to treat
When it is used
Daily treatment of :
Graves
Plummers
When:
- used to control the hypothyroidism before thyroidectomy - don’t want to give general anaesthetic to someone who is tachycardia
- Following radio iodine treatment - takes a while to work
Thionamides mechanism of action
Inhibit thyroperoxidase —
therefore inhibit iodination of thyroglobulin and the coupling of iodotyrosines –> inhibiting T3/4 synthesis and secretion
may suppress antibody production (graves)
may decrease the conversion of T4–>T3 in peripheral tissues
Why are the clinical effects of thionamides only seen weeks after they are taken, despite the biochemical effects occurring within hours?
There are a lot of stored thyroid hormone in the lumen of follicles.
They are not affected by thionamides (only newly synthesised thyroxine will be)
Unwanted actions of thionamides
Agranulocytosis (rare) - decreased neutrophils Rash (common) Headaches Nausea Jaundice Joint pain
Pharmacokinetics of thionamides
Taken orally
Carbimazole is a pro-drug. converted to Methimazole
Metabolised in liver
Excreted in the urine
Special consideration for thionamides
It can cross the placenta and is secreted into breast milk
High doses in pregnant women can cause foetal hypothyroidism
Which of the two thionamides enter the breast milk less
Propylthiouracil less than carbimazole (PTU
Role of beta blockers in thyrotoxicosis
Takes several weeks for anti-thyroid drugs to take effect
Deals with symptoms of thyrotoxicosis e.g. tremor, tachycardia, anxiety
Given non-selective beta blocker
Iodide treatment given as
It is used in combination with other drugs for…
Has a maximal effect after … days of continuous administration
Potassium iodide given as Lugol’s solution/ aqueous iodine
preparation for surgery (reduces the size and vascularity of the thyroid) severe thyrotoxicosis (thyroid storm)
10
Potassium iodide MOA
Inhibits iodination of thyroglobulin
Inhibits generation of H202
Unwanted actions of potassium iodide
Allergic reaction- rashes, fever, angioedema
Radioiodine is used to treat
Graves
Plummers (toxic nodular disease)
Thyroid cancer
Radioiodine MOA
Taken up by thyroid follicular cells and accumulates in the colloid.
From the colloid it emits beta particles of radiation that destroy the follicular cells
Discontinue anti-thyroid drugs…day before starting radio iodine and why
7-10 days
so that the thyroid gland can start working again and be really active and take up a lot of radio iodine - maximal destruction of the gland
Cautions of radioiodine
Avoid contact with small children for a few weeks
Don’t take it if pregnant or breast-feeding
Technetium scan for the 3 causes of hyperthyroidism
Graves - entire thyroid gland active. Smooth and enlarged
Plummers - only one side active, rest is suppressed
Viral thyroiditis - no activity at all
