Feline Hypothyroidism Flashcards

1
Q

What is the most common cause of hypothyroidism in cats?

A

IATROGENIC - thyroidectomy, radioiodine, anti-thyroidal drugs

(not commonly seen with thyroid (y/d) diets)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the most common result in cats following radioiodine therapy?

A

will be transiently hypothyroid for about a month, then resolve and become euthyroid within 3-6 months

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is hypothyroidism following hyperthyroid treatment so significant?

A

iatrogenic hypothyroidism causes cats to more likely become azotemic due to decreased GFR —> decreases survival times!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the most common clinical signs associated with iatrogenic hypothyroidism in cats? Why are they hard to recognize?

A
  • weight gain
  • decreased appetite
  • lethargy
    +/- dermatologic changes

signs are expected with resolution of hyperthyroidism and usually not apparent at the time of diagnosis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the screening test of choice for diagnosing feline hypothyroidism?

A

total T4

(alone does not confirm hypothyroidism - non-thyroidal illness (CKD) can make euthyroid cats look hypothyroid!)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What TSH levels are expected in hypothyroid cats? How does this test differ compared to total T4?

A

increased TSH

  • less affected by non-thyroidal illness
  • diagnosis reached with concurrent low T4 levels
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How are patients monitored following radioiodine and methimazole treatment? What is monitored?

A

RADIOIODINE = 1 mo, 3 mo, 6 mo
METHIMAZOLE = every 2-4 weeks

  • resolution of hyperthyroidism
  • detection of hypothyroidism
  • assessment of renal function
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are hypothyroid cats medically managed? When should they be rechecked? What is expected?

A

Levothyroxine without food (1 hr before meal or 3 hours after)

recheck T4 and TSH within 1 month —> T4 should be within reference range with a decrease in TSH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is survival of hypothyroid cats increased?

A

improve kidney function by supplying thyroid hormones (Levothyroxine) to increase GFR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the goal in treating cats that become hypothyroid on Methimazole? How can this be achieved?

A

mid-range T4 levels —> 1.5-3

decrease Methimazole dose by 25-50% (check TSH if concerned for non-thyroidal illness)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the monitor schedule following hypothyroisidm caused by radioiodine treatment?

A

1 month - monitor, likely to be experiencing transient hypothyroidism so treatment is not necessary quite yet

3 months - investigate with T4 and TSH +/- other basal thyroid hormones and if consistent with hypothyroidism, can treat or wait a few months if not experiencing azotemia

6 months - treat regardless of presence of azotemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the difference between overt and subclinical hypothyroidism? How does this change treatment plan?

A

OVERT = decreased T4 with increased TSH; monitor and treat at 3 and 6 months

SUBCLINICAL = normal T4 with increased TSH; monitor based on degree of azotemia (or if it is worsening)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

In what 3 ways can feline hypothyroidism be prevented?

A
  1. lower Methimazole dose
  2. delay treatment with radioiodine if TSH is not suppressed
  3. lower dose of radioiodine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly