Coral Springs Animal Hospital's Pawfessional Spring 2017 | Page 11

Although rare, iodine deficiency has been reported to cause hypothyroidism in kittens fed a strict all-meat diet. The clinical signs of congenital hypothyroidism are similar to those in dogs. Affected kittens typically appear normal at birth, but a decrease in growth rate usually becomes evident by 6-8 weeks of age. Disproportionate dwarfism develops over the ensuing months, with affected kittens developing large heads, short broad necks and short limbs. Additional findings include lethargy, mental dullness, constipation, hypothermia, bradycardia and prolonged retention of deciduous teeth. The hair coat may consist mainly of undercoat with primary guard hair scattered thinly throughout. Unlike the dog, the demand for accurate tests to assess thyroid gland function in the cat has been driven by the need to distinguish normal from hyperthyroid cats, not from those that might be hypothyroid. Measurement of baseline T4 and FT4 concentrations by equilibrium dialysis have been effective in diagnosing feline hyperthyroidism. Currently, there is no feline-specific TSH assay. Many of the tests used to asses thyroid gland function in the dog have not been critically evaluated or developed in the cat. In most situations, assessment of thyroid gland function relies on measurement of baseline serum T4 and FT4 concentrations (reference range for T4 and FT4 1-4 ng/dL). Treatment of hypothyroidism is similar for the cat and dog. Levothyroxine is the recommended thyroid hormone supplement. The initial dosage for cats is 0.05 mg or 0.1 mg orally once daily. A minimum