Chap 299 : Canine Hypothyroidism Flashcards
Drugs affecting thyroid hormone concentrations ?
Phenobarbital, Glucocorticoid, Ketoprofen, Carprofen, Sulfonamide (↑TSH), Clomipramine, Aspirin
FT4 usually not affected
Interest of TT3 ?
Low Se & Sp
Greyhoung have naturally low TT4 but normal TT3
Se/Sp of TT4
Se = 89 -100% (FN with 15% of dogs TT4AA+)
TSH stimulation test ?
Human TSH
50 - 100 µg, sample T0 - T6h
Euthyroid : stim TT4 > 1.5 T0 with TT4 > 30 nmol/L
Hypothyroid often TT4 T6h < 20 nmol/L
Biodisponibility T4 PO?
Low : 10 - 50%, halved when administered with food
Pharmacocinetiks of T4
Rapidly absorbed
Peak concentration at 3-5 hours
Half-life 9 - 15h
(Para)Clinical response to supplementation
Metabolic : days
Dermato : 1 - 3 months
Blood : anemia resolves under 3 month
Neurologic : up to 6 month
Gradual introduction of T4 supplementation ?
Might be recommanded in dogs with cardiopathy, DM, addison
Monitoring
Control at 4-6h
Administration once : 45 - 70 nmol ; thytoxicose if > 90 nmol ; insufficient if < 35 nmol
Administration twice : 35 - 55 nmol
TSH : longer term adequacy of treatment
T3 supplementation
Shorter half life, increase risk of thyrotoxicosis
Indicated if GI disease with malabsorption of T4
Congenital hypothyroidism
Hypoplasia, aplasia or dyshormonogenesis, TPO deficiency
Breed related : Tenterfield terrier, Toy fox, Rat Terriers, Papillon
Breed predisposed to TGAA
English setter, Labrador, Cocker, Rhodesian
Familial Great Dabes, Beagle, Barzoi
Dermatological sign?
80% of hT4 dogs
alopecia of nasal planum highly associated but non specific
Tragical facies
Cardiac sign
Bradycardia, Low voltage R waves, inverted T waves, BAV 1 - 2 degree
Rare atrial fibrillation or myocardial
Incidence of artherosclerosis unknown
