L1. Thyroid Endocrinology PT1 Flashcards
Thyroid regulation pathway
Thyroid Hormone:
Physiologic Effects:
Heart
Chronotropic
Inotropic
Enhance responses to circulatory catecholamines
Thyroid Hormone:
Physiologic Effect
Adipose tissue
Catabolic
Stimulate lipolysis
Thyroid Hormone:
Physiologic Effects
Muscle
Catabolic
Increase protein breakdown
Thyroid Hormone:
Physiologic Effects
Gut
Metabolic
Increase rate of carbohydrate absorption
Thyroid Hormone:
Physiologic Effect
Lipoprotein
Metabolic
Stimulate formation of LDL receptors
Thyroid Hormone:
Physiologic Effects
Other
Calorigenic
Increase metabolic rate
Total T4 (TT4) Diagnosis
Common screening test
Serum sample, randomly timed
Non-thyroidal illness and drugs can suppress TT4 (misdiagnosis)
Anti-T4 autoantibodies can interfere with assay (misdiagnosis)
Free T4 (FT4) Diagnosis
May be used as screening test
Serum sample, randomly timed
More specific than TT4 = more specific = fewer false postive
Non-thyroidal illness can suppress FT4 but effect is less than on TT4
Anti-T4 antibodies do not interfere with assay
TSH Measurement - Diagnosis
Serum sample, randomly timed, measured by immunoassay
Species-specific assay is needed
Poor screening test when used alone
Cannot be used as sole diagnostic test
More reliable when TT4 and/or FT4 levels also support the daignosis
INTERPRETATION
TSH - Normal
T4 - Normal
Condition - Normal
INTERPRETATION
TSH - Low
T4 - High
Primary Hyperthryroidism
INTERPRETATION
TSH - High
T4 - Low
Hypothryroidism Primary
INTERPRETATION
TSH - Low
T4 - Low
Hypothryroidism Secondary
Thyroid Diagnostic
Other hormone measurements
TT3, FT3, rT3 measurements
May be included on comprehensive thyroid panels
NOT useful for routine diagnosis
Anti-Thyroid Antibodies in Dogs
Anti-thyroglobulin
Anti-T4
Anti-T3
Hypothyroidism
Diminished production and secretion of thyroxine (T4) and triiodothyronin (T3)
Pathogenesis - Hypothyroidism
Lymphocytic Thyroiditis
Immune-mediated pathology/genetic influence
Presence of anti-thyroglobulin antibodies
Idiopathic follicular atrophy
Pathogensis - Hypothyroidism
Congenital (cretinism)
Potbelly
Short statur
Abnormal Mentation
May/May not be fixed with hormone
HISTORY - Hypothyroidism
Depressed mentation
Inactivity
Cold intolerance
Weight gain
Infertility - Female
EXAMINATION - Hypothyroidism
Body condition - obese
Skin and coat
Ocular
Cardiac
Neuromuscular - Functional Change due to muscle loss
Hypothyroidism
Physical Examination
Dermatologic Signs
Alopecia / slow hair regrowth - symmetric, not itching, bilateral, trunked
Dry skin with scaling
Dull brittle hair
Seborrhea
Pyoderma
Myxedema *
*Unique to thyroid disease, thick-skin around the head / face
Hypothyroidism
Physical Examination
Ocular abnormalities
Lipid Accumulation - cornea, aqueous humor, retinal vessels
Hypothyroidism
Physical Examination
Cardiac Abnormalities
Myocardial depression
Sinus bradycardia
weak apical beat
Decreased fractional shortening
Low voltage QRS complexes
Severe DCM in Great Danes - can be fixed with treatment
