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Endocrine Disease Part 1 > Feline Hyperthyroidism > Flashcards

Feline Hyperthyroidism Flashcards

1
Q

What are the advantages of antithyroid drugs for treating hyperthyroid cats?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. Effective in most cases
  2. Stabilise disease while waiting for radioiodine treatment or surgery (reduces metabolic and cardiac complications during anaesthesia)
  3. Reversibility (allows trial therapy to assess the effects of restoration of euthyroidism on renal function)
  4. Widely available
  5. Cost effective in the short term
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2
Q

What are the disadvantages of antithyroid drugs for treating hyperthyroid cats?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. Not curative
  2. Not recommended in thyroid carcinoma (rare)
  3. Minimal / no response with thyroid adenoma
  4. Iatrogenic hypothyroidism is possible
  5. Requires owner compliance
  6. Reversible
  7. Skin contact allergies
  8. Less cost effective (long term)
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3
Q

Which comes first? Carbimazole or methimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Carbimazole is the pro-drug to methimazole

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4
Q

What is the mechanism of action of methimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Acts by blocking thyroid peroxidase which inhibits the synthesis of thyroid hormones

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5
Q

Felimazole summary of product characteristics recommends a starting dose of 2.5mg twice a day based on a study that showed…

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

after 3 weeks of treatment 79% of cats were euthyroid

2.5mg dosing was also associated with less serious side effects

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6
Q

The results of two studies assessing efficacy of transdermal methimazole were discussed in this article. What were their findings?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. A randomized controlled trial with 27 cats. 2/3 became euthyroid after 4 weeks of 2.5mg bid
  2. 10 cats were given 5mg methimazole transdermally bid. All had normalised T4 levels in 28 days

Topical preparations could thus be a consideration in fractious cats

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7
Q

What were the cited results of using sustained release carbimazole (Vidalta) at a dose of 15mg sid?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Euthyroidism was acheived in 70% of 40 cats after 10 days

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8
Q

When should TT4 be monitored after initiating oral antithyroid medications?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Most cats are euthyroid within 2-3wks so they can be reassessed after that time period

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9
Q

What would be the next step if a cat is still hyperthyroid at initial testing post initiation of methimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Dose adjustments should be made in increments of 2.5mg/day until euthyroidism is acheived

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10
Q

What should be done if doses of methimazole in excess of 10mg/day are required?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Compliance should be questioned

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11
Q

What should be done if, while giving methimazole, the TT4 concentration drops below the lower end of the reference interval?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Dosage should be decreased in decrements of 2.5mg/day

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12
Q

What are the recommendations for dosing adjustments for transdermal methimazole?

With persistent hyperthyroidism or iatrogenic hypothyroidism

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

A similar scheme for oral medications is likely appropriate

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13
Q

How should the dosing of carbimazole (Vidalta) be adjusted?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Dosing can be adjusted as early as after 10 days of dosing
Adjustments should not be made in excess of 5mg

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14
Q

What are potential life threatening side effects of methimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. Hepatopathy
  2. Bleeding diathesis (in most cases with thrombocytopaenia)
  3. Marked thrombocytopaenia
  4. Agranulocytosis
  5. Myasthenia gravis
  6. Anaemia
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15
Q

What are potential non-life threatening side effects of methimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. Gastrointestinal upset
  2. Lethargy
  3. Generalised peripheral lymphadenopathy
  4. Antinuclear antibodies
  5. Mild haematological changes (leukopaenia, eosinophilia, lymphocytosis)
  6. Positive DAT (direct antiglobulin test)
  7. Dermatological reactions
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16
Q

What is the relationship between dose / dosing regimen of methimazole and the occurrence of side effects?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

No relationship could be demostrated between dose / dosing regimen with the occurrence, frequency, or severity of side effects

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17
Q

What is the general time frame between initiating methimazole therapy and seeing potential side effects?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Most appear within the first four to six weeks of therapy and become less common after 2 or 3 months of therapy

The exceptions appear to be myasthenia gravis (60-120d), anaemia (after 3 years of treatment), development of antinuclear antibodies (10-870d) and mild haematologic abnormalities (10-490d)

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18
Q

Why shouldn’t pregnant women handle methimazole and carbimazole?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

They have teratogenic potential

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19
Q

What is the recommended monitor schedule for TT4 in cats receiving antithyroid medication?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

2 to 3 weeks after starting therapy or after any dose adjustment
3 months after stabilisation
6 months thereafter

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20
Q

What are the clinical aims of antithyroid therapy?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Clinical improvement combined with results in the lower half of the reference interval
The aim for the lower half of the interval is not evidence based but resolution of clinical signs with levels just within or slightly in excess of the normal range has shown to be inadequate

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21
Q

At what time before / after methimazole administration should blood be sampled for TT4 monitoring?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

It does not matter

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22
Q

How long does it take for GFR to stabilise after acheiving a euthyroid state?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

One month

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23
Q

Increased liver values (some cases extremely elevated) are common in hyperthyroid cats. Is this significant?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Generally not. Most hyperthyroid cats have elevated liver enzymes. Even those with extremely high values usually have normal liver function.

24
Q

Do cats with hyperthyroidism and concurrently high liver enzymes require further assessment for hepatobiliary disease?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Generally not. Most hyperthyroid cats have elevated liver enzymes. Even those with extremely high values usually have normal liver function. Often values decrease following initiation of therapy (the extent and speed of change appears to depend on treatment modality)
Further assessment IS warranted in cases where
1. Values do not decrease during the first two months of therapy
2. Patient shows icterus or partial / total anorexia and does not have a typical presentation for a hyperthyroid cat

25
Q

What are the three possibilities that should be considered if elevated liver enzymes persist or continue to rise in a cat being treated for hyperthyroidism?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. Inadequate control of hyperthyroidism
  2. Progression or onset of primary liver disease
  3. Antithyroid drug induced hepatopathy
26
Q

How is renal function impacted by thyroid status?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Excessive thyroid hormone results in increased cardiac output and decreased peripheral vascular resistance. This results in an increased GFR and a subsequent decline in circulating creatinine concentration.

27
Q

How does treating hyperthyroidism potentially impact renal function?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Excessive thyroid hormone results in increased cardiac output and decreased peripheral vascular resistance. This results in an increased GFR and a subsequent decline in circulating creatinine concentration.
As thyroid hormone levels decreased with therapy, GFR decreases. The result is the potential unmasking of underlying renal function abnormalities. Azotaemia can result.

28
Q

What is the general change in GFR seen post radioiodine therapy?

Also occurs with methomazole treatment and thyroidectomy

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

There is a decrease in GFR within 4 weeks post treatment with little decline thereafter (renal parameters should therefore be reassessed one month after acheiving a euthyroid state)
It occurs with resolution of hyperthyroid state rather than being associated with treatment modality.

29
Q

In a hyperthyroid cat, why is it important to make a distinction between those with pre-treatment azotaemia and those that develop azotaemia post treatment?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Those with pre-existing azotaemia have a decreased survival time compared to those without

30
Q

What is the cited survival times for hyperthyroid cats with azotaemia vs those without?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Median survival time was 178 days for hyperthyroid cats with azotaemia / previously diagnosed CKD
vs
612 days for non-azotaemic hyperthyroid cats

31
Q

How is CKD managed in cats with / being treated for hyperthyroidism?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Treat as normal using CKD IRIS staging guidelines

32
Q

Why might the diagnosis of hyperthyroidism become difficult in a cat with concurrently existing renal disease?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

TT4 may be suppressed to a level that is within the reference interval (comparable to euthyroid sick syndrome)

33
Q

What do the authors of this paper recommend regarding the treatment of a hyperthyroid cat with IRIS stage I or II CKD?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Treatment and monitoring of hyperthyroidism should be initiated as usual using a reversible antithyroid medication (methimazole / carbimazole). If the patient shows a favourable clinical response even when euthyroidism is acheived an irreversible treatment option can be considered.

34
Q

What do the authors of this paper recommend regarding the treatment of a hyperthyroid cat with IRIS stage III or IV CKD?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

A more prudent approach is recommended.
The most conservative dosing of antithyroid medication should be pursued initially and renal parameters should be regularly monitored. If there is clinical deterioration the medication should be stopped or at least decreased.
Euthyroidism may not be achievable without deterioration of renal function. Treatment aim is then to reduce TT4 as much as possible while maintaining renal function; a hyperthyroid state may have to be maintained in this circumstance

35
Q

What is the percentage of hyperthyroid cats that are diagnosed with CKD following radioiodine therapy?

Cited by this study

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Up to 39%

36
Q

Does the speed with which thyroid hormone concentrations decrease following therapy impact the development of renal disease?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

There is no evidence to suggest that this is the case

37
Q

What impact does post treatment development of azotaemia have on the prognosis of hyperthyroid cats?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

It does not decrease survival time i.e. it has no impact

38
Q

How should the dosage of antithyroid drugs be modified in hyperthyroid patients that develop azotaemia following initiation of therapy?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

It should be maintained. It is not recommended that dosing be changed to normalise creatinine concentration

39
Q

What are the potential reasons for low creatinine in hyperthyroid cats?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. May be due to increased GFR associated with increased cardiac output and lowered peripheral vascular resistance
  2. May be due to decreased muscle mass in these patients
40
Q

Why aren’t increases in creatinine levels in treated hyperthyroid cats necessarily a reliable indicator of kidney function?

A

This is because initially low creatinine concentrations may be associated with decreased muscle mass rather than poor GFR

41
Q

Are there any biomarkers that can be used to predict the development of azotaemia in hyperthyroid cats post treatment?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

No

42
Q
A
43
Q

What is the impact of therapy with antithyroid medication onCKD IRIS staging in a hyperthyroid patient?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Treatment may increase the IRIS stage but they are unlikely to increase by more than one IRIS stage

44
Q

Why isn’t it recommended to routinely perform a trial with anti-thyroid medications prior to a more definitive treatment to assess for the development of CKD?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

This is because post treatment development of azotaemia has no impact on prognosis (and because these patients are unlikely to increase by more than one IRIS stage with therapy)

45
Q

Why is iatrogenic hypothyroidism potentially problematic when treating hyperthyroid cats?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A

Because it has been shown that azotaemia is significantly more likely in cats with iatrogenic hypothyroidism. The combination of azotaemia and iatrogenic hypothyroidism was associated with a significantly shorter survival period (456 days for hypothyroid azotaemic cats vs 905 days for hypothyroid non-azotaemic cats)

46
Q

What are the recommendations for managing cats with iatrogenic hypothyroidism?

Best practice for the pharmacological management of hyperthyroid cats with antithyroid drugs (Daminet et al 2014)

A
  1. <10nmol/L reduce the dose by 25% to 50%
  2. 10-15nmol/L (with good clinical condition and is non-azotaemic) dose adjustment is not recommended
  3. 10-15nmol/L and azotaemic the dose should be reduced
    If the dose is already at a minimum (2.5mg once a day methimazole or 10mg once a day carbimazole (assuming this is SR), then the dose should be given every 26 or 48 hours
47
Q

What were the factors found to be associated with decreased survival time in hyperthyroid cats?

Survival times for cats with hyperthyroidism treated with iodine 131 methimazole, or both: 167 cases (1996-2003)

A
  1. Age (decreased survival time in younger cats)
  2. Presence of renal disease prior to treatment
  3. Treatment type (methimazole alone had decreased survival times compared to iodine therapy alone or methimazole followwed by iodine therapy
48
Q

What are the possible reasons why hyperthyroid cats treated with methimazole alone had shorter survival times compared to methimazole followed by iodine therapy or iodine therapy alone?

Survival times for cats with hyperthyroidism treated with iodine 131 methimazole, or both: 167 cases (1996-2003)

A
  1. Potential issues with owner compliance
  2. Possible drug toxicosis
49
Q

What are the mechanisms by which hyperthyroidism can mask CKD?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

Hyperthyroidism increases GFR and decreases body muscle mass both of which result in decreased serum creatinine concentrations

50
Q

What is the source of SDMA?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

It is a byproduct of cellular metabolism. It is produced via intranuclear methyation of L-arginine residues. These residues are then released into the circulation

51
Q
A
52
Q

What is the relationship between GFR and SDMA concentrations?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

They have an inverse linear relationship. SDMA increases as GFR decreases

53
Q

What factors make SDMA a useful marker of GFR?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A
  1. It is not protein bound in plasma
  2. It is primarily eliminated via renal extrection (>90%)
  3. It is freely filtered by the glomerulus
  4. It is not secreted or reabsorbed by the renal tubules
54
Q

By what percentage does GFR need to decrease before SDMA concentrations exceed the upper reference limit?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

40%

55
Q

By what percentage does GFR need to decrease before creatinine concentrations exceed the upper reference limit?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

75%

56
Q

What are advantages of SDMA as an indicator of GFR compared to creatinine?

Evaluation of serum SDMA concentration as a marker for masked CKD in cats with hyperthyroidism (Peterson et al 2018)

A

SDMA is not affected by changes in diet or body muscle mass (unlike creatinine). It also begins to increase with much lower increases in GFR compared to creatinine (40% decrease in GFR vs 75% decrease in GFR)

57
Q
A

Endocrine Disease Part 1 (3 decks)

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