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Small Animal Medicine > Canine Hypothryoidism > Flashcards

Canine Hypothryoidism Flashcards

1
Q

What is the most common etiology of canine hypothyroidism?

A

primary hypothyroidism caused by autoimmune lymphocytic thyroiditis* or idiopathic atrophy

(secondary/tertiary = pituitary dwarfism with decreased GH and TSH)

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2
Q

What is the most common signalment associated with canine hypothyroidism?

A

middle-aged Golden Retrievers, Dobermans, Boxers, Shelties, etc.

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3
Q

What are 4 signs of hypothyroidism?

A

decreased metabolic rate

  1. lethargy
  2. weakness (myopathy)
  3. obesity
  4. exercise intolerance
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4
Q

What are the 3 most common dermatologic findings associated with canine hypothyroidism?

A
  1. bilaterally symmetrical, hyperpigmented alopecia beginning in areas of friction (initially seen as excessive shedding)
  2. dry or oily seborrhea
  3. facial myxedema - tragic facial expression
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5
Q

Is pruritis a common finding in hypothyroidism?

A

no, unless there is a concurrent cutaneous infection

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6
Q

What 5 cardiovascular findings are seen with hypothyroidism? How do patients present?

A
  1. bradycardia
  2. weak pulses
  3. muffled heart sounds
  4. low-voltage ECG complexes
  5. reduced myocardial contractility

dogs usually do not present clinically with CV changes (but cats do!)

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7
Q

How is the nervous system affected by hypothyroidism?

A

peripheral neuropathy

  • localized = facial, vestibular, front limb, larynx
  • generalized
  • megaesophagus
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8
Q

What 5 CNS abnormalities are seen with hypothyroidism?

A
  1. multifocal CNS signs
  2. hemiparesis
  3. central vestibular signs
  4. cerebellar hypermetria or ataxia
  5. multiple cranial nerve defecits - vestibular, facial, trigeminal
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9
Q

In what animals are reproductive abnormalities seen with hypothyroidism? What are 3 signs?

A

females with severe and prolonged hypothyroidism

  1. infertility
  2. increased periparturient pup mortality
  3. low birth weight
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10
Q

What is congenital hypothyroidism? What are 4 signs?

A

rare disorder in cats associated with a mutation in TSH receptors

  1. disproportionate dwarfism (open growth plates)
  2. mental dullness and lethargy
  3. broad skulls, macroglossia, delayed dental eruption
  4. ataxia, hypermetria
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11
Q

What are the 2 most common laboratory findings with hypothyroidism?

A
  1. hypercholesterolemia (must be fasted for sample!)
  2. mild nonregenerative anemia
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12
Q

What is the general flow of diagnosing hypothyroidism?

A
  • appropriate clinical signs
  • routine chemistry
  • specific thyroid function tests
  • response to treatment
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13
Q

What are the 4 thyroid function tests used to diagnose hypothyroidism?

A
  1. T4
  2. fT4
  3. TSH
  4. autoantibodies to thyroglobulin and thyroid hormones
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14
Q

What kind of test is serum total T4 for diagnosing hypothyroidism? What is required for diagnosis?

A

highly sensitive for hypothyroidism —> above low normal excludes hypothyroidism

low T4 AND classic signs

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15
Q

What commonly alters serum total T4 values?

A

T4 autoantibodies can cause false elevations

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16
Q

What is the most accurate method of measuring T4 in hypothyroid patients?

A

equilibrium dialysis for fT4

17
Q

How does equilibrium fT4 compare to serum total T4? What disadvantages are associated?

A
  • more sensitive and specific
  • less affected by non-thyroidal factors

more expensive and less readily available

18
Q

What is expected of serum TSH levels in hypothyroid patients?

A

decreased thyroid hormones causes an increase in TSH

19
Q

What is serum TSH good for diagnosing? How does it compare to other tests? What is required for hypothyroidism diagnosis?

A

early hypothyroidism where TSH is elevated and T4 and fT4 are low normal

not very sensitive

elevated TSH AND decreased T4 or fT4

20
Q

What breeds require special consideration in thyroid function tests?

A

Sighthounds - naturally low T4 and fT4

21
Q

What 4 drugs affect thyroid function tests?

A
  1. corticosteroids - test accuracy
  2. sulfonamides - induces hypothyroidism
  3. phenobarbital - mimics hypothyroidism
  4. clomipramine - test accuracy
22
Q

What is the most common affect of illness on thyroid function tests? What are 2 other possibilities? What does this result in?

A

decreased T4
- fT4 decreased (less frequent)
- elevated TSH

MIMICS HYPOTHYROIDISM - delay thyroid testing until illness is resolved

23
Q

How is thyroglobulin used to diagnose hypothyroidism?

A

naturally present in colloid and contains T4 and T3 —> antibodies against it are markers for autoimmune thyroiditis that may progress to hypothyroidism

  • not clinical = monitor, no treatment
24
Q

What do autoantibodies to T4 or T3 indicate? What is the significance of their presence?

A

autoimmune thyroiditis —> NOT hypothyroidism or hyperthyroidism

interfere with T4/T3 assays, causing false elevations that bring to hypothyroid or euthyroid range

25
Q

What test is not affected by T4/T3 autoantibodies?

A

fT4 equilibrium dialysis

26
Q

What are the most sensitive tests for diagnosing hypothyroidism? What is required for diagnosis?

A
  • T4 and fT4 = 90-98%
  • TSH = less sensitive = elevated in 65-75%

low T4/fT4 AND elevated TSH for most accurate diagnosis

27
Q

How is hypothyroidism treated?

A

Levothyroxine at an initial dose of 0.02-0.8 mg/kg QD

27
Q

How should patients respond to Levothyroxine treatment?

A

usually rapid - should have increased activity, improved attitude, and weight loss in 1-2 weeks

(dermatologic signs require months to resolve)

28
Q

What therapeutic monitoring is recommended post-pill testing with Levothyroxine? What should be done if there is poor clinical response?

A

recheck in 6-8 weeks, 4-6 hours after dose given that day

ensure adequacy of dosage, compliance, and diagnosis

29
Q

What is indicative of over-supplementation of Levothyroxine when treating hypothyroidism? What should be done if this occurs?

A

SIGNS OF HYPERTHYROIDISM!

  • PU/PD
  • panting
  • hyperactivity
  • polyphagia

stop treatment for 2-3 days then re-institute with 50-75% of original dose

Small Animal Medicine (52 decks)

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