Hypothyroidism Flashcards
Most common endocrine disease in
dogs
Frequently misdiagnosed due to
Decreased serum T4 due to illness or treatment with drugs such as trimethoprim sulphonamides, prednisolone, phenobarbitone, frusemide.
Primary vs secondary hypothyroidism
90% primary - issue with the thyroid gland
Primary causes of hypothyroidism
- Congenital - disproportionate dwarf, very rare.
2. acquired: lymphocytic autoimmune thyroiditis, idiopathic necrosis/fibrosis, neoplasia
Secondary causes of hypothyroidism
Congenital or acquired pituitary dysfunction
Tertiary causes of hypothyroidism
Very rare. Lack of hypothalamic TRH.
Congenital hypothyroidism signs
Key features: mental retardation & stunted growth.
- disproportionate body size - large heads
- dull & lethargic
- persistence of puppy coat, alopecia
‘Classic’ hypothyroidism signalment
Middle aged, pedigree dogs.
Mean age of diagnosis 7yrs. Rare <2yrs.
Golden retrievers, Dobermans, cocker spaniels and miniature schnauzers particularly at risk
‘Classic’ hypothyroidism clinical signs
Weight gain Lethargy Alopecia – bilaterally symmetrical, common over flank + hindlimbs. Pyoderma Seborrhoea Cold intolerance ‘rat tail’ Myxoedema - non-pitting 'puffiness' of the skin.
Biochemistry
Increased cholesterol, TGs, glucose, ALT ± ALP
Haematological abnormalities
Normocytic, normochromic non-regenerative anaemia.
Leptocytes (target cells) – formed in the presence of high cholesterol.
Testing
Decreased TT4 + increased TSH = highly supportive of hypothyroidism in a dog with concurrent CSs.
TT4 – useful screening test. Normal TT4 = v. unlikely to be hypothyroid.
Treatment
Levothyroxine or L-triiodothyronine
Anti-thyroglobulin antibodies
Breeders obsessed with this test!
Only 20% +ve go on to develop lymphocytic thyroidoitis.
