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Endocrine Pathophysiology > Pathophysiology of the Thyroid Gland > Flashcards

Pathophysiology of the Thyroid Gland Flashcards

1
Q

what is the primary effect of thyroid hormone?

A

increase metabolic rate and promote fetal growth and development

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2
Q

what does thyroid hormone do with erythropoiesis?

A

increases it
increases erythropoietin secretion
facilitates response to erythropoietin

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3
Q

what is the thyroglossal duct?

A

tract that thyroid tissues migrates down from the floor of the pharynx

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4
Q

failure of the thyroglossal duct to involute leads to _________________________

A

a thyroglossal cyst

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5
Q

who is congenital hypothyroidism especially common in?

A

small ruminants

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6
Q

what is the most common thyroid disease in horses and small ruminants?

A

congenital hypothyroidism

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7
Q

what type of goiter does congenital hypothyroidism cause?

A

diffuse hyperplastic goiter
nonneoplastic
noninflammatory

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8
Q

______________________ of a pregnant animal can cause congenital goiter

A

iodine deficiency

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9
Q

can iodine toxicity cause congenital hypothyroidism?

A

yes

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10
Q

what do high nitrate levels cause with the thyroid?

A

nonfunctional hypertrophy of the thyroid: inhibits ability to utilize available iodide

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11
Q

how might a pregnant mare get nitrate toxicity?

A

consumes plants or contaminated water
common grasses accumulate nitrate

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12
Q

nitrates accumulate with _________________________________

A

fertilization
drought conditions
some herbicides

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13
Q

are goitrogenic substances more likely to affect the fetus or the mother?

A

fetus

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14
Q

what does familial dyshormonogenetic goiter cause?

A

enzyme defect in thyroid hormone synthesis: impaired biosynthesis of thyroglobulin

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15
Q

what are the possible findings with congenital hypothyroidism?

A

rough haircoat, alopecia
hypothermia
weakness
stillbirths
may die within a few days of birth

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16
Q

true/false: congenital hypothyroidism can also present with CNS lesions

A

true
poor suckling, incoordination, poor righting reflexes

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17
Q

___________ is the most common thyroid disease of birds

A

goiter

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18
Q

what species of birds are goiters seen in predominantly?

A

pigeons
canaries
cockatiels
budgerigars (budgies)

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19
Q

what are some causes of goiter in birds?

A

iodine-deficient seed diet
goitrogenic substances
acute septicemia
exposure to organophosphates or chlorinated bisphenols

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20
Q

what are the clinical signs of goiter in birds often from?

A

mass effect: pressure, fluid buildup
hormone deficiency

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21
Q

what clinical signs are associated with hormone deficiency from goiter in birds?

A

immunodeficiency
depression and lethargy
abnormal skin and feathers
reproductive problems

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22
Q

what are the most common causes of canine hypothyroidism?

A

lymphocytic thyroiditis
idiopathic thyroid atrophy

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23
Q

what happens in lymphocytic thyroiditis?

A

slowly progressive destruction and fibrosis

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24
Q

what happens in idiopathic thyroid atrophy?

A

thyroid replaces with adipose tissue
degenerate follicular cells in colloid
no inflammation, antibody tests negative

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25
Q

neoplastic destruction is an ____________ cause of canine hypothyroidism

A

uncommon

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26
Q

what are some causes of neoplastic destruction of the thyroid gland that leads to canine hypothyroidism?

A

thyroid carcinoma
metastatic disease

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27
Q

is secondary hypothyroidism due to pituitary disease common?

A

no- uncommon

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28
Q

german shepherds with cystic craniobuccal (Rathke’s) pouch are deficient in ___________________ and ___________________

A

thyroid hormone
growth hormone

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29
Q

what is pituitary thyrotroph suppression a common cause of?

A

secondary hypothyroidism

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30
Q

what are some drugs that cause secondary hypothyroidism?

A

phenobarbital
glucocorticoids and NSAIDs
sulfonamides
thyroid supplements

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31
Q

what is the most common cause of feline hypothyroidism?

A

iatrogenic hypothyroidism

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32
Q

how can we cause iatrogenic hypothyroidism in cats?

A

radioactive iodine treatment
antithyroid drugs
surgical thyroidectomy

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33
Q

why is it difficult to produce hypothyroidism in dogs?

A

accessory tissue

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34
Q

what are the clinical signs of canine hypothyroidism?

A

decreased metabolic rate
dermatologic manifestations
other less common signs

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35
Q

why do hair coat manifestations occur in canine hypothyroidism?

A

hair follicles enter the telogen phase prematurely

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36
Q

what clinical signs of hypothyroidism are associated with decreased metabolic rate?

A

lethargy and mental dullness
exercise intolerance/unwillingness to exercise
tendency to gain weight with no change in food intake
obesity seen in 40-50% of cases

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37
Q

what are the laboratory abnormalities associated with canine hypothyroidism?

A

hypercholesterolemia
hypertriglyceridemia less common
nonregenerative anemia

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38
Q

what is myxedema?

A

dermal accumulation of glycosaminoglycans and hyaluronic acid
accumulates water and thickens skin: tragic facial expression

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39
Q

what are some less common signs of canine hypothyroidism?

A

neuromuscular
reproductive
cardiovascular

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40
Q

what are some cardiovascular signs of canine hypothyroidism?

A

abnormal rhythms or bradycardia
occasional atherosclerosis with hyperlipidemia

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41
Q

what are the available tests for canine hypothyroidism?

A

total T4 and T3
free T4
endogenous TSH
function tests
autoantibody assays

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42
Q

who can you perform an endogenous TSH test on?

A

dogs and cats only

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43
Q

what are some things that affect thyroid hormones?

A

age, breed, reproductive status
non-thyroid illness

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44
Q

changes in hormone-protein binding can affect _______________

A

total T4

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45
Q

how can changes in hormone-protein binding affect total T4?

A

negative feedback on TSH from increased fT4 will result in lower total T4
fT4 is more rapidly cleared

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46
Q

true/false: some drugs can cause displacement of T4 from proteins

A

true: cortisol

47
Q

how sensitive is free T4 by equilibrium dialysis?

A

sensitive: 80-98%

48
Q

decreased free T4 is strongly suggestive of primary hypothyroidism but _______________________________

A

not a definitive diagnosis

49
Q

what will the value of a free T4 direct assay be increased by?

A

anti-T4 antibody

50
Q

what does increased TSH suggest with endogenous canine TSH?

A

hypothyroidism

51
Q

why is endogenous canine TSH not a good screening test for primary hypothyroidism?

A

20-40% of hypothyroid dogs have normal TSH

52
Q

true/false: autoantibodies may provide prognostic information but are not diagnostic for hypothyroidism

A

true

53
Q

how common is adult primary hypothyroidism in equines?

A

rare

54
Q

what can secondary hypothyroidism in equines be due to?

A

pituitary pars intermedia dysfunction
drugs
nonthyroidal illness
food deprivation
zinc, copper, iodine, endophyte-infected fescue

55
Q

how common is feline hyperthyroidism?

A

very common in older cats

56
Q

what is the etiology of feline hyperthyroidism?

A

multinodular hyperplasia or benign follicular adenomas

57
Q

true/false: if you can feel a thyroid gland in a cat (thyroid slip), the cat is hyperthyroid

A

false: not all cats with nodules are hyperthyroid

58
Q

what are the clinical signs of feline hyperthyroidism?

A

weight loss
polyphagia
hyperactivity
change in behavior
coat changes
vomiting
pu/pd
cardiac disturbances

59
Q

what are some cardiac abnormalities associated with feline hyperthyroidism?

A

increased heart rate and contractility
left ventricular concentric hypertrophy

60
Q

what are some laboratory abnormalities associated with feline hyperthyroidism?

A

erythrocytosis +/- macrocytosis
stress leukogram
elevated liver enzymes
azotemia
hyperphosphatemia

61
Q

how many cats with feline hyperthyroidism have azotemia?

A

25%

62
Q

can you use total T3 to diagnose feline hyperthyroidism?

A

not reliable

63
Q

what is the single best test to diagnose feline hyperthyroidism?

A

total T4

64
Q

why would you perform a T3 suppression test?

A

measure T3 to asses compliance or occult disease

65
Q

if you have a cat that matches feline hyperthyroidism but the TT4 is low or normal, what should you do?

A

repeat TT4 in a week or two
fT4
T3 suppression test
thyroid scintigraphy

66
Q

in thyroid neoplasma, nonfunctional adenomas (benign) are common in ____________________________

A

older cats, horses, and ponies

67
Q

what type of thyroid neoplasm are dogs more likely to get?

A

nonfunctional thyroid carcinomas

68
Q

what does calcitonin from C cells (parafollicular cells) do?

A

acts to decrease calcium concentration

69
Q

what does calcitonin do to renal tubular reabsorption?

A

decreases it of calcium and phosphorous

70
Q

thyroid C cell neoplasms are most commonly functional in ___________

A

bulls

71
Q

what does thyroid hormone do to increase metabolic rate and promote fetal growth and development?

A

peripheral regulation by T3 and T4
thermogenesis: O2 consumption and ATP hydrolysis
fetal: neurological and skeletal development
neonatal growth

72
Q

what is circulating T4 and T3 bound to?

A

thyroxine-binding globulin
transthyretin
other carrier proteins

73
Q

what does thyroid hormone do with lipids?

A

stimulates synthesis
increases plasma fatty acids and cholesterol synthesis
stimulates degradation/excretion of lipids

74
Q

cholesterol and triglycerides are _____________ related to hormone level

A

inversely

75
Q

what does thyroid hormone do with carbohydrate metabolism?

A

enhances insulin action
increases gluconeogenesis and glycogenolysis
increases GI tract carbohydrate absorption

76
Q

what does thyroid hormone do with the cardiovascular system?

A

increases heart rate, contractility, and output
vasodilation: enhances perfusion

77
Q

what is a thyroglossal cyst filled with?

A

fluid or mucus

78
Q

who is a thyroglossal cyst most commonly found in?

A

dogs and pigs

79
Q

what is the most common thyroid disease in horses and ruminants?

A

congenital hypothyroidism

80
Q

what happens in congenital hypothyroidism?

A

neonatal disease: problem in mother
decreased T3/T4 levels
increased TSH stimulates gland hyperplasia

81
Q

what can cause congenital hypothyroidism?

A

iodine deficiency
iodine toxicity
nitrate toxicity
goitrogenic cubstances
familial dysshormonogenetic goiter

82
Q

what happens in iodine toxicity that leads to congenital hypothyroidism?

A

decreased thyroid hormone production and secretion
inhibits iodine uptake
inhibits proteolysis of thyroglobulin
accumulation in colloid but no release into blood

83
Q

what do soybeans contain that inhibits thyroperoxidase?

A

genistein

84
Q

what do cabbages contain that inhibit iodine binding and thyroperoxidase?

A

isothiocyanates

85
Q

who has familial dyshormonogenetic goiter been reported in?

A

sheep: corriedale, merino, romney
cattle: afrikander
goats: saanen dwarf
pigs

86
Q

what does a goiter look like?

A

neck tissues thickened and edematous
bilaterally enlarged lobes
lobes firm and dark red

87
Q

true/false: mild signs may improve when thyroid gland matures and produces its own hormones for congenital hypothyroidism

A

true

88
Q

those born with low T4 levels at birth may _________________ to supplementation
those born with normal T4 levels at birth may ___________________ to supplementation

A

respond
not respond

89
Q

what does the pressure on the heart and major vessels, crop, and esophagus cause in avian goiter?

A

sudden death
loss of voice, weight loss
wheezing, difficulty swallowing

90
Q

can avian goiter be palpated?

A

may or may not

91
Q

what can the clinical signs of avian goiter be due to?

A

mass effects
hormone deficiency

92
Q

what reproduction problems are caused by avian goiter?

A

decreased hatchability
increased embryo mortality

93
Q

what autoantibodies are increased in immune-mediated lymphocytic thyroiditis?

A

thyroglobulin Ab
colloid antigen Ab
thyroperoxidase Ab

94
Q

what can cause lymphocytic thyroiditis?

A

immune-mediated
genetic link
triggered by infection?
defect in suppressor T cells?

95
Q

what is advanced lymphocytic thyroiditis characterized by?

A

replacement of thyroid follicle with adipose tissue

96
Q

is thyroid carcinoma functionally active?

A

not usually

97
Q

who is congenital pituitary disease common in? can lead to secondary hypothyroidism

A

german shepherds: cystic craniobuccal pouch
giant schnauzers and boxers: TSH deficiency

98
Q

what is pituitary thyrotroph suppression often due to?

A

nonthyroidal illness or drugs
any severe disease
hyperadrenocorticism
phenobarbital, sulfas, NSAIDs, steroids

99
Q

who is myxedema seen in?

A

severe, longstanding cases of canine hypothyroidism

100
Q

what function tests do we have for canine hypothyroidism?

A

TSH stimulation test
T3 suppression test

101
Q

what does non-thyroidal illness cause regarding thyroid?

A

decreased albumin
impaired protein binding
decreased cellular uptake of fT4
increased liver metabolism
decreased TSH and/or TRH secretion

102
Q

what makes total T4 a good screening test for hypothyroidism?

A

sensitivity 90-95%
hypothyroidism unlikely if T4 within normal limits

103
Q

is a low TT4 concentration enough to diagnose primary hypothyroidism?

A

no

104
Q

who is total T3 useful for?

A

sighthounds: TT4 and fT4 lower than most, but TT3 is not

105
Q

what does decreased fT4 indicate in a free T4 equilibrium dialysis?

A

strongly suggestive but not definitive diagnosis for canine hypothyroidism

106
Q

what will the value of a free T4 direct assay be increased by?

A

anti-T4 antibody

107
Q

is endogenous canine TSH a good screening test for primary hypothyroidism?

A

no

108
Q

very low TT4 with appropriate clinical ssigns and laboratory results ____________ diagnostic

A

may be

109
Q

how is low TT4 usually confirmed?

A

fT4 and/or TSH

110
Q

who is at decreased risk for feline hyperthyroidism?

A

siamese
himalayan

111
Q

what is the etiology/cause of feline hyperthyroidism?

A

genetic
decreased expression of G proteins
overexpression of c-ras oncogenes
environmental factors

112
Q

what are the cardiac signs of feline hyperthyroidism?

A

tachycardia
systolic murmur
gallop rhythms
dyspnea due to pleural effusion

113
Q

how is free T4 useful in feline hyperthyroidism?

A

more sensitive than total T4 in cats with subclinical disease
occasionally normal with concurrent non thyroid illness
occasionally high with non thyroid illness

Endocrine Pathophysiology (6 decks)

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