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DMod3 Pt6 Endocrine Disease > DM3 Pt6-1 Hyperthyroidism > Flashcards

DM3 Pt6-1 Hyperthyroidism Flashcards

1
Q

What is the most common feline endocrinopathy?

A

Hyperthyroidism is the most common feline endocrinopathy.

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2
Q

What are the histological types of most feline thyroid tumors?

A

The majority of thyroid tumors are benign, classified as adenomatous hyperplasia or adenomas.

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3
Q

In what percentage of hyperthyroid cats are both thyroid glands involved?

A

Both thyroid glands are involved in approximately 75% of hyperthyroid cats.

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4
Q

What environmental factors have been speculated to contribute to hyperthyroidism in cats?

A

Feeding tinned food (especially fish or liver-flavored), indoor living, use of cat litter, flea sprays, fertilizers, insecticides, and herbicides.

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5
Q

What is the potential link between thyroid glands and the development of hyperthyroidism?

A

A circulating factor may influence both glands, leading to speculation about autocrine or paracrine growth factors, circulating thyroid stimulators, or genetic mutations in TSH receptors.

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6
Q

What percentage of hyperthyroid cats have malignant thyroid carcinomas?

A

Malignant thyroid carcinomas occur in 1-3% of hyperthyroid cats.

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7
Q

How can malignant thyroid carcinomas present in hyperthyroid cats?

A

They can be solitary masses in one lobe, involve both lobes, present as multiple nodules in the cervical region, or exist as ectopic tissue beyond the thoracic inlet.

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8
Q

What is the difference between functional and non-functional thyroid carcinomas?

A

Functional carcinomas cause hyperthyroidism, while non-functional carcinomas do not.

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9
Q

Why is histopathology important after thyroidectomies in hyperthyroid cats?

A

Adenomas and carcinomas cannot be distinguished clinically or by gross appearance, so thyroid tissue should be submitted for histopathology to confirm the diagnosis.

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10
Q

What are the classic clinical signs of hyperthyroidism in cats?

A

Weight loss, polyphagia, and tachycardia.

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11
Q

Why is hyperthyroidism being detected earlier in cats now?

A

Veterinarians are identifying cases before the classic signs appear, sometimes detecting goitre incidentally or noticing less common signs like vomiting or restlessness.

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12
Q

What is ‘apathetic hyperthyroidism’?

A

A condition where hyperthyroid cats exhibit inappetence and lethargy instead of the usual polyphagia and hyperactivity.

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13
Q

What complicates the clinical picture in hyperthyroid cats?

A

Concurrent illness, which is common in older cats.

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14
Q

What percentage of hyperthyroid cats experience weight loss?

A

92% of hyperthyroid cats experience weight loss.

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15
Q

What percentage of hyperthyroid cats have polyphagia?

A

61% of hyperthyroid cats have polyphagia.

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16
Q

What percentage of hyperthyroid cats exhibit polydipsia/polyuria?

A

47% of hyperthyroid cats exhibit polydipsia and polyuria.

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17
Q

What percentage of hyperthyroid cats have increased activity or restlessness?

A

40% of hyperthyroid cats show increased activity or restlessness.

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18
Q

What are some less common signs of hyperthyroidism in cats?

A

Tremors (7%), panting (23%), muscle weakness (10%), and neck ventroflexion (<1%).

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19
Q

What percentage of hyperthyroid cats experience vomiting?

A

38% of hyperthyroid cats experience vomiting.

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20
Q

What skin changes may occur in hyperthyroid cats?

A

Skin changes like patchy alopecia, matting, dry coat, seborrhoea, or thin skin occur in 36% of hyperthyroid cats.

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21
Q

What percentage of hyperthyroid cats exhibit lethargy?

A

11% of hyperthyroid cats exhibit lethargy.

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22
Q

What percentage of hyperthyroid cats have a palpable goitre?

A

Around 90% of hyperthyroid cats have a palpable goitre, though a recent study reported only 72% in a referral population.

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23
Q

Is a palpable goitre always indicative of hyperthyroidism?

A

No, a palpable goitre is not pathognomonic for hyperthyroidism, as non-active thyroid nodules or other cervical masses may be present.

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24
Q

What is the definitive diagnostic test for hyperthyroidism?

A

An elevated serum total T4 concentration is the definitive test for hyperthyroidism in most cases.

25
Q

Why should T4 samples be sent to an external lab?

A

In-house T4 analysers are not very reliable, so samples should be sent to a reliable external laboratory.

26
Q

In what percentage of hyperthyroid cats is elevated total T4 alone sufficient for diagnosis?

A

Elevated total T4 alone is enough to confirm hyperthyroidism in more than 90% of cases.

27
Q

What should be done if total T4 is normal in a cat suspected of being hyperthyroid?

A

Repeat the total T4 and exclude non-thyroidal illness. If still normal, perform a free T4 test by equilibrium dialysis.

28
Q

What are other diagnostic tests for hyperthyroidism if T4 levels remain normal?

A

T3 suppression test, TRH stimulation test, or thyroid scintigraphy.

29
Q

What is thyroid scintigraphy used for in hyperthyroid cats?

A

It helps diagnose hyperthyroidism, determine the location of hyperfunctional tissue, and assess whether surgery or radioactive iodine therapy is needed.

30
Q

What percentage of hyperthyroid cats may have ectopic thyroid tissue?

A

Around 3-15% of hyperthyroid cats may have ectopic thyroid tissue, with the higher figure observed in referral populations.

31
Q

Why is it important to discuss the potential for ectopic thyroid tissue with cat owners before surgery?

A

Ectopic thyroid tissue can cause recurrence of hyperthyroidism, so owners should be informed of the possibility and the option of referral for further evaluation.

32
Q

Can thyroid scintigraphy distinguish between adenomas and carcinomas?

A

No, thyroid scintigraphy cannot distinguish between thyroid adenomas and carcinomas based on their appearance.

33
Q

What are the three main treatment options for hyperthyroidism in cats?

A

Surgical thyroidectomy, medical management with methimazole or carbimazole, and radioactive iodine treatment.

34
Q

What are the disadvantages of long-term medical treatment for hyperthyroidism?

A

Life-long treatment, regular monitoring, and potential side effects such as anorexia, vomiting, hepatopathies, facial pruritus, and haematological disorders.

35
Q

What are some serious side effects associated with methimazole?

A

Hepatopathies, haematological disorders, and in some cases, unexplained coagulopathies.

36
Q

What is the recommended approach to starting methimazole treatment?

A

Start with a low dose and increase to effect if no adverse signs are observed.

37
Q

How is transdermal methimazole used, and where is it commonly used?

A

Transdermal methimazole is applied to the skin and has been widely used in the US with good results in some cats.

38
Q

What is the benefit of using carbimazole over methimazole for treating hyperthyroidism?

A

Carbimazole, especially in its slow-release form (Vidalta®), allows for once-daily dosing, which improves client compliance.

39
Q

Why is medical management useful in some hyperthyroid cats?

A

It is useful for cats with concurrent disorders that increase the risk of anesthesia or radioactive iodine treatment, and for stabilizing hyperthyroid cats before surgery.

40
Q

Why should hyperthyroid cats undergo a trial treatment with methimazole before irreversible treatments?

A

To re-assess renal function once the cat becomes euthyroid, especially if there is evidence of renal dysfunction.

41
Q

What is the main risk associated with surgical thyroidectomy in cats?

A

The development of post-operative hypoparathyroidism and subsequent hypocalcaemia.

42
Q

How is post-operative hypoparathyroidism treated in cats after thyroidectomy?

A

Most cases resolve with time, but short-term treatment with calcium supplementation and vitamin D may be required. In rare cases, long-term treatment with vitamin D and calcium supplementation is needed.

43
Q

Why is it important to stabilize hyperthyroid cats medically before surgery?

A

Stabilization reduces the risk associated with anesthesia during thyroidectomy.

44
Q

What is the primary disadvantage of radioactive iodine treatment for hyperthyroidism?

A

Limited availability and the required post-treatment isolated hospitalisation time.

45
Q

Which type of hyperthyroidism is radioactive iodine particularly effective in treating?

A

It is the treatment of choice for functional thyroid carcinomas, though a higher dose (about 10 times) is needed compared to adenomatous hyperplasia.

46
Q

How does radioactive iodine (I-131) work to treat hyperthyroidism?

A

Iodine-131 is concentrated in the thyroid gland, where its radiation destroys hyperfunctional thyroid cells, while leaving surrounding tissues unharmed due to the short travel distance of β-particles.

47
Q

What percentage of cats become euthyroid after a single radioactive iodine treatment?

A

Over 95% of cats become euthyroid after a single treatment.

48
Q

Does methimazole interfere with radioactive iodine treatment?

A

The consensus now is that methimazole does not interfere with radioactive iodine treatment, though this is still controversial.

49
Q

Why do cats require isolation after radioactive iodine treatment?

A

Cats must remain in isolation until their radioactivity levels decrease due to the long half-life of iodine-131 (8.1 days).

50
Q

What are some advantages of performing thyroid scintigraphy before radioactive iodine treatment?

A

It helps visualize the location of hyperfunctional thyroid tissue, assess whether surgery is an option, and detect ectopic tissue that would make surgery ineffective.

51
Q

What are indications for radioactive iodine treatment?

A

Lack of palpable goitre, ectopic intrathoracic thyroid tissue, large thoracic inlet nodules, functional thyroid carcinoma, contraindications for anesthesia, or owner preference.

52
Q

What are contraindications for radioactive iodine treatment?

A

Concurrent diseases (e.g., neoplasia, diabetes), severe complications (e.g., congestive heart failure), uncontrolled hyperthyroidism with complications, poor hospital adaptation, or owner reluctance.

53
Q

Is renal insufficiency a contraindication for radioactive iodine treatment?

A

No, the presence of renal insufficiency is no longer a contraindication if renal function has been evaluated after stabilization with methimazole or carbimazole.

54
Q

What prescription diet is used to manage hyperthyroidism in cats?

A

Hill’s y/d, an iodine-restricted diet.

55
Q

How does the Hill’s y/d diet work to manage hyperthyroidism?

A

The ultra-low iodine levels in the diet restrict the production of thyroid hormone, lowering T4 levels.

56
Q

What is a major advantage of using Hill’s y/d to manage hyperthyroidism?

A

It allows hyperthyroidism management without sedation or anesthesia and may reduce short-term costs.

57
Q

What is the main drawback of using the Hill’s y/d diet for hyperthyroid cats?

A

The diet must be fed exclusively, with no additions, as external sources of iodine (e.g., hunting, other food) can stimulate T4 production.

58
Q

Why might the Hill’s y/d diet not be suitable for some older or diabetic cats?

A

It is relatively high in carbohydrates, which may not be ideal for diabetic, obese, or older cats.

59
Q

Does the Hill’s y/d diet treat the underlying condition of hyperthyroidism?

A

No, like medical management, it only controls the symptoms by reducing thyroid hormone production without treating the underlying condition.

DMod3 Pt6 Endocrine Disease (5 decks)

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