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Hypothyroidism in dogs - Coggle Diagram

- - - - Lymphocytic thyroiditis
      - Idiopathic atrophy
      - neoplastic destruction
      - Iodide deficiency
      - Drugs
    - - Pituitary tumors
      - Infection / trauma / surgery / drugs
  - - - Autosomal recessive
      - Peroxidase deficiency
      - Toy Fox Terriers, Rat Terriers, Spanish Water Spaniel, Tenterfield Terrier
      - Panhypopituitarism
    - - Giant Schnauzer
      - Boxer
      - extremely rare
    - - Excess/deficiency of iodide
- - - - English setter,
      - Doberman pincher
      - Maltese,
      - Cocker spaniel
      - Beagle
      - Sight hounds: in general have lower levels normally
  - - - Spares the head/face
      - not inflammed
    - - Secondary seborrhea
      - pyoderma
      - Pruritus (secondary skin infection)
    - - Weight gain
      - Thermophilia
      - Lethargy, exercise intolerance
    - - sinus bradycardia
      - weak apex beat
      - low PR waves
- - - - good screening test
      - Non-thyroidal illness and drugs can lower T4 concentration
      - Very sensitive but non-specific
      - Low basal T4 requires further evaluation of the thyroid function
    - - Nonthyroidal illness and drugs can also lower fT4 concentration but less often than TT4
      - More specific than TT4
    - - Primary Hypothyroidism:
        
        Higher than normal
        
        low circulating and pituitary T4 and T3 levels = TSH secretion
      - Secondary: Lower than normal
      - Advantages
        
        One blood sample required
        
        Cheaper than TSH stimulation test
        
        Less affected by illnesses and drugs
      - Disadvantages:
        
        20 to 40 % of hypothyroid dogs have normal serum endogenous TSH
        
        15% of euthyroid dogs have elevated serum TSH
      - should not be used as sole test
      - Combine it with T4 and fT4d
    - - Very accurate test: 6-hour test
      - Only human recombinant TSH available
      - Very expensive
    - - Important to diagnose sub-clinical lymphocytic thyroiditis
      - A positive test is not diagnostic
      - About 20% of positive dogs will develop hypothyroidism in one year
      - may be required by some breed registries
    - - Not a very accurate test
      - Most of the T3 hormone is produced inside the cells
      - Circulating levels do not reflect whole body concentration
    - - More important
        
        Non-thyroidal illness
        
        Correlation with severity
        
        Drugs - examples
        
        Glucocorticoids
        
        Potentiated sulfas
        
        Clomipramine
        
        NSAIDs
        
        Phenobarbital
      - Still important
        
        Age
        
        Breed
        
        Sight hounds:↓T4, ↓ fT4
        
        Random fluctuation
        
        Fasting
- - - - Lethargy and weakness should resolve in 7 to 10 days
      - Hair regrowth may take 12 weeks
    - - Measure post-pill T4 levels after 6 weeks of therapy
      - Collect sample 4 to 6 hours post-pill if dosing twice daily: peak concentration
      - T4 values should be at or slightly above the upper limit of the reference interval
      - If dosing once daily, sample immediately before the daily dose (trough level)
      - T4 values should be within the reference interval