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27 Cards in this Set
- Front
- Back
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Describe the Hypothalamic-Pituitary-Thyroid Axis
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Hypothalamus releases TRH > Pituitary releases TSH > Thyroid releases T3/T4 > T3/T4 shut off TRH/TSH
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Thyroid Hormone is produced by:
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Follicular epithelium of the Thyroid
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T3:T4 ratio
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1:4
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Main job of T4
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Shut off TRH & TSH
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How is T3 produced?
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Peripheral deiodination of T4
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Conditions when you're most likely to see an increase in reverse T3
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Illness, starvation, catabolism
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Physiologic effects of Thyroid Hormones
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Increased Basal Metabolic Rate
+ calorigenesis + protein/enzyme synthesis + muscle/adipose catabolism Regulation of cholesterol metabolism Increased strength of heart contractions & frequency + erythropoiesis |
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Two types of acquired Primary Hypothyroidism
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1. Lymphocytic thyroiditis
2. Idiopathic Follicular Atrophy |
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Iatrogenic causes of Primary Hypothyroidism
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Surgery
Radioactive Iodine Therapy Anti-thyroid medication |
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DDX for Acquired Secondary Hypothyroidism
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Neoplasia
Pituitary suppression via glucocorticoids Severe illness Malnutrition |
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DDX for Congenital Secondary Hypothyroidism
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Cystic Rathke's Pouch
ADH deficiency |
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Hypothyroid is common in these breeds:
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Golden Retrievers
Doberman Pinchers English Setters Rhodesian Ridgebacks |
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Clinical Signs for Hypothyroid
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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 |
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Cardiovascular effects of Hypothyroidism
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Sinus bradycardia
Weak apex beat ECG - low voltage complexes Echo - decreased fractional shortening |
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Rare Clinical signs of Hypothyroidism
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Ocular changes
Non-specific GI changes Pancreatitis Peripheral Neuropathy Myopathy Cranial nerve dysfunction Reproductive dysfunction |
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These are sometimes seen concurrent to hypothyroidism
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IDDM
HoAC HoPT Gonadal Failure Anemia |
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Chemistry Panel for Hypothyroidism
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Hypercholesterolemia*
Lipemia High ALP AST ALT Hyponatremic |
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Total T3 Test measures:
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Systemic T3. This is undesirable because much of circulating T3 is created due to extra-thyroidal deiodination of T4.
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What test would you use to differentiate between Hypothyroidism and Euthyroidism?
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TSH Stim Test.
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Presence of thyroid autoantibodies is both sensitive and specific for what condition?
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Thyroiditis.
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3 conditions that should be met before considering a therapeutic trial:
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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 |
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In relation to Thyroid hormones, glucocorticoids:
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lower tT4, fT4, and tT3
Lower T4>T3 conversion Lower TSH (sometimes) |
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In relation to Thyroid hormones, Phenobarbital:
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Lowers tT4, fT4, and tT3
Lowers TSH (sometimes) |
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In relation to Thyroid hormones, TMS:
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Lowers tT4 & fT4
Lowers TSH (sometimes) |
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Pharmaceutical treatment options for HoT:
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Soloxine (levothyroxine)
Hair will fall out, but regrow. Recheck at 4 weeks |
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Clinical Signs of Thyrotoxicosis:
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Panting
PU/PD polyphagia weight loss |
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Most common Clin path findings of HoT patients
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Hi TAG (88%)
Hi Cholesterol (75%) ALP in the hundreds (Cushing's dogs in the 1000's) |
