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27 Cards in this Set

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Describe the Hypothalamic-Pituitary-Thyroid Axis
Hypothalamus releases TRH > Pituitary releases TSH > Thyroid releases T3/T4 > T3/T4 shut off TRH/TSH
Thyroid Hormone is produced by:
Follicular epithelium of the Thyroid
T3:T4 ratio
1:4
Main job of T4
Shut off TRH & TSH
How is T3 produced?
Peripheral deiodination of T4
Conditions when you're most likely to see an increase in reverse T3
Illness, starvation, catabolism
Physiologic effects of Thyroid Hormones
Increased Basal Metabolic Rate
+ calorigenesis
+ protein/enzyme synthesis
+ muscle/adipose catabolism
Regulation of cholesterol metabolism

Increased strength of heart contractions & frequency
+ erythropoiesis
Two types of acquired Primary Hypothyroidism
1. Lymphocytic thyroiditis
2. Idiopathic Follicular Atrophy
Iatrogenic causes of Primary Hypothyroidism
Surgery
Radioactive Iodine Therapy
Anti-thyroid medication
DDX for Acquired Secondary Hypothyroidism
Neoplasia
Pituitary suppression via glucocorticoids
Severe illness
Malnutrition
DDX for Congenital Secondary Hypothyroidism
Cystic Rathke's Pouch
ADH deficiency
Hypothyroid is common in these breeds:
Golden Retrievers
Doberman Pinchers
English Setters
Rhodesian Ridgebacks
Clinical Signs for Hypothyroid
Dull
Lethargic
Exercise Intolerance
Obese without polyphagia
Cold intolerance
Dry Skin and haircoat
Bilaterally symmetrical alopecia (TH triggers anagen phase)
Rat Tail
Bridge of nose
Hyperpigmentation
Seborrhea
Lichenification
Comedones
Recurrent infections
Myxedma
Cardiovascular effects of Hypothyroidism
Sinus bradycardia
Weak apex beat
ECG - low voltage complexes
Echo - decreased fractional shortening
Rare Clinical signs of Hypothyroidism
Ocular changes
Non-specific GI changes
Pancreatitis
Peripheral Neuropathy
Myopathy
Cranial nerve dysfunction
Reproductive dysfunction
These are sometimes seen concurrent to hypothyroidism
IDDM
HoAC
HoPT
Gonadal Failure
Anemia
Chemistry Panel for Hypothyroidism
Hypercholesterolemia*
Lipemia
High ALP AST ALT
Hyponatremic
Total T3 Test measures:
Systemic T3. This is undesirable because much of circulating T3 is created due to extra-thyroidal deiodination of T4.
What test would you use to differentiate between Hypothyroidism and Euthyroidism?
TSH Stim Test.
Presence of thyroid autoantibodies is both sensitive and specific for what condition?
Thyroiditis.
3 conditions that should be met before considering a therapeutic trial:
1. Signs consistent with HoT.
2. Non-thyroidal illness ruled out.
3. Low tT4, Low normal T4 with + autoantibody, or normal tT4 with high TSH
In relation to Thyroid hormones, glucocorticoids:
lower tT4, fT4, and tT3
Lower T4>T3 conversion
Lower TSH (sometimes)
In relation to Thyroid hormones, Phenobarbital:
Lowers tT4, fT4, and tT3
Lowers TSH (sometimes)
In relation to Thyroid hormones, TMS:
Lowers tT4 & fT4
Lowers TSH (sometimes)
Pharmaceutical treatment options for HoT:
Soloxine (levothyroxine)

Hair will fall out, but regrow.
Recheck at 4 weeks
Clinical Signs of Thyrotoxicosis:
Panting
PU/PD
polyphagia
weight loss
Most common Clin path findings of HoT patients
Hi TAG (88%)
Hi Cholesterol (75%)
ALP in the hundreds (Cushing's dogs in the 1000's)