PATHOLOGY - Hyperthyroidism Flashcards
Which species is more prone to hyperthyroidism?
Cats
What is the cause of hyperthyroidism?
Hyperthyriodism is caused by functional neoplasia of the thyroid gland which produce excess thyroid hormone and increase the body’s metabolic rate
Which functional neoplasms cause hyperparathyroidism?
Adenoma (most common)
Adenocarcinoma
(T/F) Functional neoplasia of the thyroid is usually unilateral
FALSE. Functional neoplasia of the thyroid is typically bilateral, which is atypical of most neoplasia and can indicate that these tumours are induced by various risk factors
What are the possible risk factors for hyperthyroidism?
Remember the true risk factors are unknown
Age
Genetics
Low iodine diet
Canned foods
Goitrogens
What are goitrogens?
Goitrogens are compounds containing thiocynate which competes with iodine for absorption by the thyroid gland, leading to insufficient thyroid hormone production, compensatory thyromegaly (known as goitre) and increased thyroid hormone production
Which specific goitrogens could be associated with the development of hyperthyroidism in cats?
Flame retardants such as polybrominated diphenyl ethers could be associated with hyperthyroidism in cats as most surfaces are treated with flame retardants, so much so it is now found in dust which cats can groom off of themselves and ingest
This is not known for sure but could be a possibility
What is the typical signalement for hyperthyroidism?
Cats over 8 years old with a gradual onset of clinical signs
What are the potential clinical signs of hyperthyroidism?
Weight loss (key sign)
Polyphagia
Tachycardia
Vomiting
Diarrhoea
Poor coat quality (starry appearance)
Behavioural changes
What behavioural changes can be seen in cats with hyperthyroidism?
Cats with hyperthyroidism can be hyperactive, very friendly and/or very aggressive. In these patients behaviour can change very rapidly
What would you typically find on clinical examination in a cat with hyperthyroidism?
Low body condition score (BCS)
Dehydration
Poor coat quality
Tachycardia
Cardiac murmur
Thyroid nodule
Often difficult to handle
How can hyperthyroidism cause a cardiac murmur?
Hyperthyroidism increases metabolic rate resulting in tachycardia and increased cardiac workload which will result in a compensatory myocadiac hypertrophy which can result in structural changes and a resulting heart murmur
(T/F) Cats with hyperthyroidism can die very suddenly
TRUE. Cats with hyperthyroidism can die suddenly, especially when stressed. This is most likely due to tachycardia progressing to fatal ventricular arrhythmias
How do you palpate a thyroid nodule?
Lift the cats head and tilt it to the side slightly. Assess each side of the trachea individually by running your finger from the jaw, down the side and round the back of the trachea to the thoracic inlet. If you feel a pop, you have felt a thyroid nodule which is a key sign of thyroid neoplasia
Why does hyperthyroidism increase liver enzymes on biochemistry?
Hyperthyroidism increases the metabolic rate, including the livers metabolic rate, which can cause an increase in liver enzymes on biochemistry
How does hyperthyroidism affect serum urea and creatinine levels?
Hyperthyroidism will cause hypertension which will increase the hydrostatic pressure in the glomeruli and consequently increase the glomerular filtration rare (GFR). This will increase the excretion of urea and creatinine. However, be aware that cats with hyperthyroidism often concurrently present with kidney disease which would normally increase serum urea and creatinine levels. Hyperthyroidism will mask the degree of kidney disease by increasing GFR and excretion of urea and creatinine
How do you definitively diagnose hyperthyroidism?
Measure serum T4 levels
Which changes in serum T4 levels are a hallmark of hyperthyroidism?
If the serum T4 levels are elevated beyond 60nmol/l, this is a hallmark of hyperthyroidism. However, patients with hyperthyroidism can also have concurrent disease which will result in sick euthyroid syndrome which will decrease the serum T4 levels, so it is important to use your clinical judgement
What should you be aware of when handling cats with hyperthyroidism?
Cats with hyperthyroidism can be very aggressive and stress can cause sudden death, so, it is very important to handle them with care and use sedation when needed. Try and keep them in their carrier where possible as they will feel more secure and minimise stressors as much as possible. It is also important to provide them with high energy feed little and often as these patients are polyphagic
How should you approach taking blood samples from cats with hyperthyroidism?
Have everything organised before taking the cat out of the kennel
Sedate if necessary
Secure well
Do not use clippers
Tap their nose with a pen when taking blood
What are the four treatment options for hyperthyroidism?
Low iodine diet
Drugs
Thyroidectomy
Radiotherapy
How does a low iodine diet help to manage hyperthyroidism?
Iodine is a key component in the synthesis of thyroid hormones and thus limiting the amount of iodine in the diet can reduce the functional neoplastic production of thyroid hormone
What is important to inform owners about when converting their cat to a low iodine diet?
It is important to make owners aware that the transition to a low iodine diet has to be done very slowly (over 3 - 4 weeks) or the cat will refuse to eat the food. It is important not to mix the new feed with the old feed to start with, seperate the two to start with and slowly begin to incorporate it when you see the cat begin to eat the new food
What are the limitations of a low iodine diet when managing hyperthyroidism?
Low iodine diets will not work if the cat is a scavenger
Will not stop the tumour from growing and eventually producing more thyroid hormone
Which drugs can be used in the treatment of hyperthyroidism?
Methimazole
Carbimazole
What is the difference between methimazole and carbimazole?
Carbimazole is a pro-drug which will be converted into methimazole within the body
What is the most affective frequency of administration for methimazole?
Methimazile is most affective when initially adminsitered twice daily, however, when the patient is stabilised you can reduce the frequency to once daily
What are the limitations of methimazole and carbimazole in the treatment of hyperthyroidism?
Challenging to give tablets to cats
Cats often refuse the ingest the liquid formulations of these drugs
Lots of potential side effects
Will not stop the tumour from growing and eventually producing more thyroid hormone
What are the potential side effects of methomazole and carbimazole?
Vomiting
Diarrhoea
Anorexia
Thrombocytopenia
Hepatotoxicity
Self excoriation
What are the potential complications of a thyroidectomy?
Haemorrhage
Hypocalcaemia
How can a thyroidectomy cause hypocalcaemia?
A thyroidectomy can cause damage to the parathyroid gland and thus result in hypocalcaemia
How do you treat hypocalcaemia secondary to a thyroidectomy?
It is important to administer both calcium and activated vitamin D3 (calcitriol) which is involved in calcium absorption. It is very important to adminsiter activated vitamin D3 as if the parathyroid gland has been damaged or removed, it will not be able to convert vitamin D2 to vitamin D3
What is radiotherapy in the treatment of hyperthyroidism?
Radiotherapy for hyperthyroidism typically involves radioactive iodine therapy where a single subcutaneous injection of radioactive iodine-131 is administered. This radioactive iodine-131 will be absorbed by the thyroid gland and emit radiation which will destroy the thyroid and neoplastic tissue and thus reduce thyroid hormone production
How much does radiotherapy typically cost when treating hyperthyroidism?
Approximately £2500 to £3000
Which factors should you consider when choosing the most appropriate treatment for hyperthyroidism?
Patient factors
Client factors
Clinical factors
