Canine Hypothyroidism

Key clinical signs

-weight gain

-lethargy

-alopecia

-pyoderma

-other skin changes

Most common cause of hypothyroid in dogs/most common reason for misdiagnosis

-lymphocytic thyroiditis

-misdiagnosis commonly from suppression of hypothalmic-pituitary stimulation of thyroid due to illness (euthyriod sick syndrome)

Hormones synthesized by the thyroid gland

T4- thyroxine, T3- triiodothyronine

Effects of thyroid hormone on the body

-increased metabolic rate

-oxygen consumption

-heart rate

-erythropoiesis

-catecholamine release

-catabolic for muscle and adipose tissue

General clinical signs

-weight gain, obestiy

-lethargy

-alopecia - often bilaterally symmetric over the lateral trunk, tail, and ventral thorax

-pyoderma, hyperkeratosis, seborrhea, hyperpigmentation

-bradycardia, weak pulse, low voltage ECG complexes

Diagnosis of hypothyroid (findings and testing)

BW: mild non regen anemia, hypercholesterolemia

-serum total T4: preferred screening test

-normal T4 is not hypothyroid

-low T4 levels need to be confirmed by at least one: tx any identified underlying cause, cTSH and free T4 by equilibrium dialysis levels (hypothyroid dogs should have increased cTSH and low free T4), TSH stim test (low T4 even after stim is hypothyroid), trial of T4 replacement therapy and assess response

Treatment

-oral admin levothyroxine

-optimal dosing vries among dogs and T4 levels should be evaluated after starting therapy and while treatment is maintained

-dose should be calculated based on ideal body weight