Hyperthyroidism Flashcards
What is hyperthyroidism?
Excessive production of thyroxine (T4) caused by adenomatous hyperplasia of the thyroid glands
What does the thyroid do?
Produces T3 and T4 which increase sympathetic stimulation
Signalment/Presentation
Middle aged/old cats
Often aggressive/overactive
Weightless with polyphagia
vomiting
Diarrhoea
Hyperactivity
PUPD
Muscle wastage
How does hyperthyroidism affect the heart?
Leads to tachycardia and hypertrophic cardiomyopathy
Secondary hypertrophic heart as consequence of hypertension
What is euthyroid sick syndrome?
Non-thyroidal disease that affects thyroid levels
Diagnostic approach
Presentation/history
Palpable goitre
Presentation as heart failure
Specific tests
* Total T4 - best test
* Free T4
* T3
* TSH
Treatment options
Do nothing
Radioactive iodine
Surgery
Anti-thyroid medication
Dietary management
What is Radioactive iodine?
- Administration of 131I (radioactive iodine) – subcutaneous injection
- Simple and effective
○ Single injection - No side effects
- No anaesthesia
- Requires licensing and hospitalization facilities
- Cats become ‘radioactive’ – have to be isolated
- Curative but expensive
Considerations for surgery
65% of cats have bilateral hyperthroidism
Must be careful not to remove parathyroid (controls phosphorus/calcium regulation)
Required GA
Medication options
Anti-thyroid drugs
* Carbimazole/methimazole
Prevents thyroid hormone being produced but doesn’t address tumour - can be malignant
Side effects of anti-thyroid medication
Anorexia
Vomiting
Lethargy
Face ad neck excoriation
Dyscrasia (leukaemia, anaemia, thrombocytopaenia
Hepatopathy
Indications for dietary management
When definitive treatment is not possible
Cat can’t be medicated
Side effects from medication
Issues with dietary management
Must be fed exclusively this diet
Questionable palatability
Low protein
Non-negotiable management
Clinical exam
* BCS/MCS
* Fundic exam/blood pressure
Weight check
Nutritional assessment
Physiology
- Thyroid hormones increase basal metabolic rate and heat production
○ This means more energy is being used up so cats lose weight and have increased appetite
○ Using more energy than being taken in
Breakdown of tissues
Breakdown of muscles to use protein for gluconeogenesis
