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Module 17 > Hyperthyroidism > Flashcards

Hyperthyroidism Flashcards

1
Q

what are the causes of hyperthyroidism

A

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

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2
Q

what are the risk factors of hyperthyroidism

A

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

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3
Q

what are possible causes of hyperthyroidism

A

Age

Diet

Long term iodine levels

Goitrogens:

Other sources (flame retardants)

Canned food

Genetics

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4
Q

what are clinical signs of hyperthyroidism

A

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

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5
Q

what is the signalment of hyperthyroidism in cats

A

no sex or breed predisposed

8 years or older

gradual onset

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6
Q

what can be seen on clinical exam of hyperthyroidism

A

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

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7
Q

describe some clinical and physical exam findings of hyperthyroidism

A
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8
Q

what are ddx of weight loss in older cats

A

Hyperthyroidism

Chronic renal failure

Diabetes mellitus

Cardiomyopathy

Neoplasia

Inflammatory bowel disease

Chronic hepatic disease

Chronic pancreatitis

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9
Q

what are ddx for behavioural changes in older cats

A

Painful diseases:

Arthritis

Pancreatitis

Hypertension

Metabolic disease:

Any systemic illness

Neurological diseases:

Neoplasia

?FIV, feline cognitive dysfunction

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10
Q

how is hyperthyroidism diagnosed

A

total T4 levels

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11
Q

what are serum T4 concentrations that are indicative of hyperthyroidism

A
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12
Q

what are handling considerations when dealing with a hyperthyroid cat

A

Don’t fight with the cat

Use your brain

Use drugs

Dismantle the crate to get cat out

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13
Q

how would you look after a hyperthyroid cat (3)

A

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

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14
Q

how would you obtain a blood sample from a hyperthyroid cat

A

Issues:

Risks, hematomas

Methods:

Get ready first

Slowly apply restraint

Don’t use clippers

Be quick, tap nose with pen

Consider sedation (ketamine, midazolam)

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15
Q

how do you treat hyperthyroidism

A

Can be managed with oral antithyroid medications, thyroidectomy, radioactive iodine, or an iodine restricted diet

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16
Q

what are the features of a hyperthyroid diet

A

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

17
Q

what is the drug of choice to treat hyperthyroidism

A

Methimazole

18
Q

what is the dose used of methimazole

A

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

19
Q

how does methimazole work

A

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

20
Q

how long does it take to bring T4 down to normal levels after administered methimazole

A

3-15 days

clinical improvement takes about 1 week longer

21
Q

which is better methimazole SID or BID

A

BID is better to bring down T4 levels

22
Q

what are the side effects of methimazole

A

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

23
Q

what is another drug to treat hyperthyroidism

A

Carbimazole

24
Q

how does carbimazole work

A

Converted to methimazole

Less bitter, fewer adverse reactions

25
Q

what is the dose of carbimazole used

A

Human formulation

5mg TID PO (q8h)

Sustained release formulation

10-15 mg SID PO (q24h)

26
Q

what are the side effects of carbimazole

A

Side effects are uncommon

Same as methimazole

27
Q

why is it important to recheck hyperthyroidism cats

A

need to check frequently to see if clinical signs are improving

history, physical exam, total T4, CBC, full biochem, liver, renal profiles, urinalaysis, blood pressure

28
Q

what is the surgical treatment for hyperthyroidism

A

thyroidectomy

29
Q

what needs to occur before surgery

A

anesthetic risk

need to stabilize before surgery (T4 levels need to be normalized)

30
Q

what are the complications of thyroidectomy

A
  1. hemorrhage
  2. hypocalcemia
  3. voice changes
31
Q

how do you manage hypocalcemia post surgery

A
  1. muscle twitching
  2. ears twitching, teeth grinding
  3. tetanic seizures

1 ml calcium gluconate slowly IV

250 mg/kg BID or TID PO calcium gluconate

vit D analogues

32
Q

what is another option for treatment

A

injection of radioactive iodine 131

33
Q

how do you decide which treatment to administer

A

Patient factors:

Uncomplicated cases

Complicated cases

Owner factors:

Financial

Practical

Clinical factors:

Experience

Facilities

34
Q

how do you assess the patient in hyperthyroidism

A

clinical assessment: hematology and biochem, urinalysis, fecal analysis etc

practical assessment: temp, reaction to stress

35
Q

why does hyperthyroidism often cause renal disease

A

1. Increased thyroid hormone:

Increased heart function

Increased blood pressure

Increased kidney function

Implications:

Diagnosis

Therapy

If we treat hyperthyroidism we may unmask kidney failure

36
Q

what are thyroid carcinomas

A

2% of hyperthyroid cats

often refractory to methimazole/carbimazole

37
Q

what are the treatment options of thyroid carcinomas

A

surgical excision

radioactive iodine

radiotherapy

38
Q

what is the difference between feline hyperthyroidism and canine hypothyroidism

A

Module 17 (31 decks)

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