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Hypothyroidism in dogs: pathophysiology, causes and clinical presentation



Hypothyroidism is the most common endocrine disorder in dogs. Primary hypothyroidism is most common, resulting from primary thyroid gland failure associated with either lymphocytic thyroiditis or idiopathic follicular atrophy, both of which occur at approximately equal frequency. Lymphocytic thyroiditis is considered an immune-mediated disease, whereas the pathogenesis of idiopathic follicular atrophy is unknown. Secondary hypothyroidism results from failure of the pituitary gland, and accounts for less than 5% of cases.