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SP2 Endocrine > Lecture 12 3/27/25 > Flashcards

Lecture 12 3/27/25 Flashcards

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1
Q

What are the characteristics of canine hypothyroidism prevalence?

A

-common, but still only seen in less than 1% of dogs
-commonly diagnosed and misdiagnosed

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2
Q

What is tertiary hypothyroidism?

A

dysfunction of the hypothalamus leading to TRH deficiency

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3
Q

What is secondary hypothyroidism?

A

failure of the pituitary gland leading to decreased TSH

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4
Q

What is primary hypothyroidism?

A

dysfunction of the thyroid gland itself

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5
Q

Which type of hypothyroidism is most common?

A

primary hypothyroidism

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6
Q

What are the characteristics of congenital hypothyroidism?

A

-rare
-typically causes early death and may go undiagnosed
-defect can be anywhere in hypothalamus-pituitary-thyroid axis

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7
Q

What are some examples of congenital hypothyroidism in which the animals survive?

A

-pituitary dwarfs
-congenital secondary hypothyroidism in giant schnauzers
-congenital primary hypothyroidism with goiter in terrier breeds

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8
Q

What are the possible causes of primary hypothyroidism?

A

-lymphocytic thyroiditis
-thyroid atrophy
-neoplasia
-congenital
-drugs
-surgery

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9
Q

Which causes of primary hypothyroidism account for 95% of cases?

A

lymphocytic thyroiditis and thyroid atrophy

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10
Q

What are the characteristics of lymphocytic thyroiditis?

A

-diffuse cellular infiltration
-immune-mediated
-clinical signs occur with > 80% destruction
-slowly progressive over 1 to 3 years
-suspected that genetics, environment, and/or infection can be initiative

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11
Q

What are the characteristics of thyroid atrophy?

A

-thyroid parenchyma is replaced by adipose tissue with no inflammatory cells
-idiopathic
-suspected to be the end-stage of lymphocytic thyroiditis

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12
Q

What are the characteristics of neoplastic destruction of the thyroid?

A

-infiltrative tumor arises from thyroid gland or via metastasis
-most thyroid tumors are unilateral
-hypothyroidism secondary to thyroid destruction occurs in less than 10% of thyroid tumor cases

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13
Q

Which drug types can cause animals to develop clinical hypothyroidism disease?

A

-anti-thyroid drugs
-sulfa drugs

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14
Q

What is the approach to treating hypothyroidism caused by drugs?

A

-withdrawal of the offending drug
-supplementation with thyroid hormones as needed

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15
Q

What are the characteristics of iodine involvement in hypothyroidism development?

A

-iodine deficiency can cause hypothyroidism, but is rare
-iodine excess can inhibit iodine uptake and thyroid hormone secretion

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16
Q

What are the iatrogenic causes of hypothyroidism?

A

-surgery, especially thyroidectomy
-radioiodine therapy

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17
Q

What is the typical signalment for hypothyroidism dogs?

A

-typically middle-age, but can be any age
-varied age of onset based on breed
-no recognized gender predilection
-more common in neutered animals
-mid to large breed dogs

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18
Q

Which dog breeds have a predisposition for hypothyroidism?

A

-golden retrievers
-doberman pinschers
-labrador retrievers
-cocker spaniels

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19
Q

What are the characteristics of hypothyroidism clinical presentation?

A

-slow, progressive onset of signs
-signs not evident until > 80% of thyroid function is lost
-subtlety of signs varies with age, breed, and type of coat

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20
Q

What percent of hypothyroidism dogs present with dermatologic signs?

A

around 85%

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21
Q

What are the dermatologic signs of hypothyroidism?

A

-bilateral truncal alopecia
-rat tail
-loss of guard hairs/”puppy” coat
-seborrhea
-chronic otitis
-hyperpigmentation
-secondary pyoderma

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22
Q

What are the characteristics of myxedema?

A

-severe hypothyroidism
-excess mucopolysaccharides and hyaluronic acid accumulate in dermis and bind water
-results in “tragic facial expression”

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23
Q

What are the clinical signs of myxedema coma?

A

-obtunded mental state
-hypothermia
-hypotension
-bradycardia
-hypoventilation

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24
Q

What are the metabolic signs of hypothyroidism?

A

-decline in metabolic rate
-lethargy
-overweight/obese
-weakness
-cold intolerance
-cardiovascular signs/bradycardia
-NO PU/PD

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25
What are the neurological abnormalities that can occur in hypothyroidism?
-polyneuropathy -focal neuropathy -cervical spondylomyelopathy -megaesophagus -CNS signs
26
What are the cardiovascular abnormalities that can occur in hypothyroidism?
-sinus bradycardia -decreased fractional shortening/contractility changes
27
What are the reproductive abnormalities that can occur in hypothyroidism?
female: -infertility -shortened estrus -prolonged estrual bleeding -prolonged anestrus -galactorrhea male: -infertility -testicular atrophy
28
What are the ocular abnormalities that can occur in hypothyroidism?
-corneal lipid deposits -KCS -anterior uveitis -lipemic aqueous humor
29
What hematology abnormality is seen in 35% of hypothyroidism dogs?
mild to moderate normocytic, normochromic, non-regenerative anemia
30
What serum chemistry abnormalities can be seen in hypothyroidism dogs?
-mildly increased liver enzymes (ALT, AST, ALP) -mildly increased creatinine kinase -fasting hypercholesterolemia -fasting hypertriglyceridemia
31
What does the hyperlipidemia associated with hypothyroidism put dogs at risk for?
-atherosclerosis -increased ALP -proteinuria -pancreatitis -gallbladder sludge -gallbladder mucocele
32
What must be considered in the diagnostic approach to hypothyroidism patients?
-patients should have clinical signs and/or CBC/chem changes to consider testing -must have something to monitor -should only pursue testing once they are free of other illnesses -animals empirically treated for hypothyroidism with thyroxine should be off supplementation for at least 1 week prior to testing
33
What are the characteristics of T4?
-main hormone secreted -normal range of 1.0 to 4.0
34
What are the characteristics of T3?
-most active -T4 is converted to T3 intracellularly
35
What are the characteristics of total T3 measurement?
-very little T3 is secreted by thyroid gland -cannot distinguish normal vs. hypothyroid vs. euthyroid sick based on T3 measurement -minimal value in measuring
36
What are the characteristics of free T3 measurement?
-diagnostic value is unknown -may be low in very advanced hypothyroidism
37
what are the characteristics of total T4 measurement?
-measures total amount of circulating thyroxine -tends to be lower with increasing age -greater than 90-95% of hypothyroid dogs have low T4 -can be affected by T4 autoantibodies or illness
38
What are the characteristics of euthyroid sick syndrome?
-occurs with nonthyroidal illness -total T4 is low despite patient NOT having hypothyroidism -T4 improves once non-thyroidal illness resolves -therapy not required -should retest after non-thyroidal illness resolves
39
Which breeds can have a T4 measurement below the reference interval in health?
-greyhound -sloughi -scottish deerhound -alaskan sled dog -basenji
40
Which dog breeds have their own breed-specific T4 reference intervals?
-alaskan malamute -collie -golden retriever -keeshond -samoyed -siberian husky -greyhound -sloughi
41
Which drug classes can cause a low total T4 measurement?
-glucocorticoids -phenobarbital -sulfa drugs** (causes clinical signs) -tricyclic antidepressants
42
When should a total T4 be run?
-otherwise healthy patient with hypothyroidism signs -ruling out hypothyroidism -alone or in combo with TSH to monitor thyroid supplementation
43
What are the characteristics of free T4?
-measures non-protein bound thyroxine fraction -measured via equilibrium dialysis -single best test; best combo of sensitivity, specificity, and accuracy -can be low with drugs, illness, and/or breed
44
What are the characteristics of TSH measurement?
-expected to be increased in dogs with hypothyroidism -in reality, some hypothyroid dogs have normal TSH and some normal dogs have high TSH -high TSH with concurrently low TT4 or fT4 is very supportive of primary hypothyroidism dx
45
What are the characteristics of thyroglobulin autoantibodies?
-suggest presence of autoimmune thyroiditis -do not predict current thyroid status -could be a marker for future hypothyroidism -may be affected by recent vx
46
Which combination of tests provides the best sensitivity for hypothyroidism?
TT4 + fT4 + TSH
47
Which combination of tests provides the best specificity for hypothyroidism?
fT4 + TSH
48
Which combination of tests is best for determining if drugs or non-thyroidal illness are causing hypothyroidism?
fT4 or TT4 + TSH + autoantibody testing
49
What are the characteristics of hypothyroidism testing?
-having at least 2 tests that support a hypothyroid diagnosis provides > 98% of correct diagnosis -tests should be used to confirm clinical suspicion
50
What are other possible diagnostic tests for hypothyroidism?
-TSH stim. -TRH stim. -scintigraphy -ultrasound -trial therapy
51
What are the characteristics of hypothyroidism treatment?
-supplementation with sodium levothyroxine/L-thyroxine -illegal to use non-FDA approved products; stick with Thyro-Tabs or ThyroKare -good bioavailability -treatment is lifelong
52
What are the steps to take in patients with reduced dose considerations for thyroid supplementation (i.e. heart dz, diabetes, cushing's)?
-start with 50% dose to avoid rapid changes in metabolic rate -slowly increase dose to tolerable levels -in the event of myxedema coma, give IV levothyroxine
53
What is the prognosis for hypothyroidism?
-excellent for acquired hypothyroidism -guarded for myxedema coma
54
Which clinical signs should be monitored for improvement in hypothyroid dogs?
-mentation and activity: improvement within days -anemia: improvement within weeks -neuro/derm/cardio signs: improvement within months
55
How should clinical reassessment of hypothyroid patients occur?
-reassess clinical signs -measure T4 and TSH 4 to 8 weeks after beginning treatment -goal is to achieve normal T4 and TSH readings with control of clinical signs
56
What can cause hypothyroidism treatment to fail?
-poor owner compliance -incorrect dose -generic thyroid drugs -decreased bioavailability -poor absorption from GI tract (concurrent GI dz) -misdiagnosis
57
What are the characteristics of feline hypothyroidism?
-very rare -typically iatrogenic; following hyperthyroidism treatment -syndrome resolves with time
58
What are the clinical signs of feline hypothyroidism?
-lethargy -obesity -derm. signs -cardiovascular signs -dwarfism -azotemia
59
How is feline hypothyroidism diagnosed?
TT4 or fT4 measurement
60
When is levothyroxine treatment indicated in cats?
-clinical signs present -azotemia -hypothyroidism does not resolve within 3 to 6 months
61
What is the prognosis for feline hypothyroidism?
-good prognosis for primary hypothyroidism with appropriate therapy -guarded prognosis for kittens with congenital hypothyroidism due to skeletal and neurological abnormalities

SP2 Endocrine (22 decks)

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