Med I - Canine Hypothyroidism

Front 1

Thyroid hormones
-normal function

Back 1

Increase basal metabolic rate and oxygen consumption
-inc. HR and contractility
-catabolism of muscle and fat
-regulate lipid metabolism
-normal growth and development

Front 2

Hypothyroidism
-results in

Back 2

-sluggish
-low energy
-overweight

Front 3

Canine hypothyroidism
-pathology

Back 3

-lymphoplasmacytic thyroiditis
-idiopathic follicular atrophy
-congenital

uncommon:
-secondary
-tertiary
-iatrogenic

Front 4

2 most common causes of canine hypothyroidism

Back 4

-lymphoplasmacytic thyroiditis
-idiopathic follicular atrophy

Front 5

Pathology

Back 5

-lymphoplasmacytic thyroiditis

Front 6

Canine hypothyroidism
-signalment

Back 6

-medium age
-possibly more in neutered dogs
-Breeds: golden retriever, Doberman,
--beagle, borzoi, (lymphoplasmacytic thyroiditis)
-- toy fox terrier, rat terrier (congenital hypothyroidism)

Front 7

Canine hypothyroidism
-clinical signs (types)

Back 7

-general
-dermatologic
-neurologic
-cardiovascular
-reproductive
-ocular

-congenital form
-myxedema coma

Front 8

Canine hypothyroidism
-general clinical signs

Back 8

-lethargy
-mental dullness
-weight gain
-exercise intolerance
-cold intolerance

Front 9

Canine hypothyroidism
-dermatologic clinical signs

Back 9

-dry skin
-bilaterally symmetric alopecia (tail, ventrum, trunk)
-hyperpigmentation
-seborrhea
-myxedema
-secondary infections

Front 10

Myxedema
-definition

Back 10

-deposition of mucopolysaccharides in the skin

Front 11

Canine hypothyroidism
-neurologic clinical signs

Back 11

-peripheral neuropathy (weakness, ataxia, cranial nerve deficits [V, VII, VIII])
-rare central signs (seizure, disorientation, coma)

Front 12

Canine hypothyroidism
-cardiovascular clinical signs

Back 12

-bradycardia
-dec. cardiac contractility
-atherosclerosis

Front 13

Canine hypothyroidism
-reproductive clinical signs

Back 13

Female
-anestrus
-uterine intertia
-small litters
-weak puppies

Male
-dec. libido
-oligospermia
-testicular atrophy

Front 14

Canine hypothyroidism
-congenital clinical signs

Back 14

-mental dullness
-stunted, disproportionate growth
-retained puppy coat

Front 15

Canine hypothyroidism
-Myxedema coma clinical signs

Back 15

-rare

-mental depression
-hypothermia
-non-pitting edema
-respiratory depression

Front 16

canine hypothyroidism
-clin path abnormalities

Back 16

-mild nonregenerative anemia
-hypercholesterolemia
-hypertriglyceridemia

Front 17

Canine hypothyroidism
-diagnostic tests

Back 17

-total/free T4
-total/free T3
-TSH
-TSH response test
-auto-antibodies
-adjunctive tests (imaging, biopsy)

Front 18

Types of T4 that can be measured

Back 18

-Total T4
-Free T4

Front 19

T4 that's metabolically active in tissues

Back 19

-Free T4

Front 20

T4 test that's better for measuring Canine hypothyroidism

Back 20

-equilibrium dialysis (free T4)

Front 21

Why is free T4 a better reflection of thyroid status in canine hypothyroidism?

Back 21

less affected by:
-protein levels
-drugs
-nonthyroidal illness

Front 22

Canine Thyroid Stimulating Hormone (cTSH)
-aka

Back 22

-Thyrotropin

Front 23

cTSH levels in hypothyroid dogs

Back 23

-should be increased due to a lack of negative feedback from T4
combine with TT4 or fT4

Front 24

Specificity
-define

Back 24

-ability to say with certainty that a disease is present

Front 25

Canine hypothyroidism
-test with the best specificity

Back 25

Combo tests
-low TT4 & High TSH
-low fT4 & high TSH

Front 26

Canine hypothyroidism
-gold standard diagnostic test

Back 26

-TSH Response Test

Front 27

TSH Response Test
-procedure

Back 27

-rhTSH given IV
-TT4 measured 6 hrs later
-normal animal should have increased TT4
-hypothyroid should have blunted response

$$$$$

Front 28

Canine hypothyroidism
-types of imaging

Back 28

-nuclear scintigraphy
-ultrasound

Front 29

Canine hypothyroidism
-why so difficult to diagnose?

Back 29

-nonthyroidal illness (euthyroid sick syndrome) can decrease TT4
-drugs affect thyroid function tests

Front 30

Canine hypothyroidism
-nonthyroidal illnesses that can decrease TT4

Back 30

-hyperadrenocorticism
-diabetic ketoacidosis
-hypoadrenocorticism
-renal failure
-hepatic dz
-peripheral neuropathy
-heart failure
-infection
-surgery

Front 31

Should low TT$ be treated in euthyroid sick syndrome patients?

Back 31

-no
-only supplement animals with thyroid illness

Front 32

Canine hypothyroidism
-drugs affecting thyroid function tests

Back 32

-glucocorticoids
-anti-epileptics
-sulfonamides
-NSAIDs
-clomipramine
-amiodarone, propranolol
-heparin
-radiocontrast agents

Front 33

Canine hypothyroidism
-treatment

Back 33

Levothyroxine supplementation (T4)
-0.1 mg/10 lb PO BID
-up to 0.8 mg PO BID (but can go higher for larger dogs)

need to monitor after administration because some dogs are very good absorbers and can become hyperthyroid

Front 34

Canine hypothyroidism
-can we supplement with T3

Back 34

-yes, but T4 allows tissues to autoregulate how much is used

Front 35

Canine hyperthyroidism
-timeline for response to treatment

Back 35

-1-2 wks: improved energy
-6-8 wks: weight loss, improved myocardial function
-8-12 wks: neurologic resolution
-2-6 mo: dermatologic resolution

Front 36

Canine hypothyroidism
-treatment monitoring

Back 36

-recheck TT4 in one month
-check TT4 4-6 hrs post levothyroxine pill
-TT4 should be normal or slightly high

Thyroid supplementation wears off in 1-2 months

Front 37

Canine hypothyroidism
-treatment with myxedema coma

Back 37

-supportive care (fluids, passive rewarming, ventilator support)
-levothyroxine 4-5 ug/kg IV BID

Front 38

Canine hypothyroidism
-treatment with concurrent dilated cardiomyopathy

Back 38

-supplementation at 25-50% dose

Front 39

Canine hypothyroidism
-treatment with concurrent hypoadrenocorticism

Back 39

-glucocorticoid and mineralocorticoid supplementation first

Front 40

Feline hypothyroidism
-treatment

Back 40

-levothyroxine .05-.1 mg/Cat/day