Hyperthyroidism Flashcards
what are the causes of hyperthyroidism
Excessive production and secretion of T4 and T3 by the thyroid gland and is almost always a result of chronic intrinsic disease in one or both thyroid lobes
One or more usually small, discrete masses can be palpable in the ventral region of the neck in most cats
Follicular cell adenoma and multinodular adenomatous hyperplasia are the most common histological findings
Both are benign and both may occur together within the same thyroid lobe
Less common are thyroid adenomas
what are the risk factors of hyperthyroidism
Most common endocrine disease affecting cats older than 8 years —> average age is 13 years
No sex predisposition
Domestic short hair and long haired cats are most commonly affected breeds
Siamese and Himalayans are at decreased risk
Canned food
Litter trays
Ectoparasiticides
what are possible causes of hyperthyroidism
Age
Diet
Long term iodine levels
Goitrogens:
Other sources (flame retardants)
Canned food
Genetics
what are clinical signs of hyperthyroidism
Classic clinical signs are weight loss and muscle wasting (which may progress to cachexia)
Polyphagia
Restlessness or hyperactivity
Haircoat changes
Patchy alopecia
Matted hair
Minimal or excessive grooming behaviour
PUPD
Vomiting
Diarrhea
Some cats develop aggressive behaviour that resolves in response to successful treatment of the hypothyroid state
what is the signalment of hyperthyroidism in cats
no sex or breed predisposed
8 years or older
gradual onset
what can be seen on clinical exam of hyperthyroidism
Thin
Dehydrated
Poor hair coat
Tachycardia (220/min)
Cardiac murmur
Thyroid nodule
Often difficult to handle
Handle with care! Hyperthyroidism can sensitize the heart to catecholamines —> adrenaline surge can lead to fatal arrhythmias
describe some clinical and physical exam findings of hyperthyroidism
what are ddx of weight loss in older cats
Hyperthyroidism
Chronic renal failure
Diabetes mellitus
Cardiomyopathy
Neoplasia
Inflammatory bowel disease
Chronic hepatic disease
Chronic pancreatitis
what are ddx for behavioural changes in older cats
Painful diseases:
Arthritis
Pancreatitis
Hypertension
Metabolic disease:
Any systemic illness
Neurological diseases:
Neoplasia
?FIV, feline cognitive dysfunction
how is hyperthyroidism diagnosed
total T4 levels
what are serum T4 concentrations that are indicative of hyperthyroidism
what are handling considerations when dealing with a hyperthyroid cat
Don’t fight with the cat
Use your brain
Use drugs
Dismantle the crate to get cat out
how would you look after a hyperthyroid cat (3)
1. Environment:
NO dogs!
Experienced nurses
Hiding places
2. Feeding:
Most hyperthyroid cats are hungry
Weight loss is very common
Vomiting is common
3. Diet:
High energy, low fat diet
Little and often
how would you obtain a blood sample from a hyperthyroid cat
Issues:
Risks, hematomas
Methods:
Get ready first
Slowly apply restraint
Don’t use clippers
Be quick, tap nose with pen
Consider sedation (ketamine, midazolam)
how do you treat hyperthyroidism
Can be managed with oral antithyroid medications, thyroidectomy, radioactive iodine, or an iodine restricted diet
what are the features of a hyperthyroid diet
Iodine restricted diet
Restricts T4 production
Analogous to methimazole
Switch diet slowly otherwise it won’t work
Not an instant cure, it can take months
what is the drug of choice to treat hyperthyroidism
Methimazole
what is the dose used of methimazole
One tablet (2.5 mg) BID PO — can double if needed
Can maintain some cats on SID dosing
BID is best at a lower dose
how does methimazole work
Inhibits the synthesis of thyroid hormone by blocking the incorporation of iodine into the tyrosyl groups in thyroglobulin and by prevent the coupling of these to T3 and T4
how long does it take to bring T4 down to normal levels after administered methimazole
3-15 days
clinical improvement takes about 1 week longer
which is better methimazole SID or BID
BID is better to bring down T4 levels
what are the side effects of methimazole
15% show side effects
Most are very mild — vomiting, anorexia
Do not require withdrawal of medication
Some transit hematological abnormalities
Severe side effects
Self excoriation
Hepatotoxicity
Thrombocytopenia
what is another drug to treat hyperthyroidism
Carbimazole
how does carbimazole work
Converted to methimazole
Less bitter, fewer adverse reactions
