A comprehensive review of canine hypothyroidism: Clinical features, laboratory diagnosis, and therapeutic approaches
Author(s): Kalakappa and Abhijith SP
Abstract: Canine hypothyroidism is among the most frequently diagnosed endocrine disorders in dogs, yet remains one of the most diagnostically challenging. This review summarizes the current understanding of its epidemiology, pathophysiology, diagnostic approach, and therapeutic management. Primary hypothyroidism, most often the result of lymphocytic thyroiditis or idiopathic follicular atrophy, accounts for the majority of cases. Clinical manifestations are diverse and often nonspecific, reflecting metabolic and dermatologic changes. Diagnostic evaluation requires careful interpretation of thyroid function tests, including total thyroxine (TT4), free thyroxine (fT4 by equilibrium dialysis), endogenous thyroid-stimulating hormone (TSH), and thyroglobulin autoantibodies (TgAA). The TSH stimulation test, while historically considered the gold standard, is now reserved for equivocal cases due to limited availability of recombinant human TSH. Consideration of non-thyroidal illness and drug effects is essential to avoid misdiagnosis. Levothyroxine remains the treatment of choice, with dosing tailored to body weight, clinical response, and serum hormone monitoring. Most dogs show clinical improvement within weeks of initiating therapy, and long-term prognosis is excellent with appropriate management. Advances in immunogenetics and longitudinal studies of thyroid autoimmunity continue to refine understanding of disease progression. Current consensus guidelines emphasize a combined diagnostic approach, judicious therapeutic monitoring, and individualized patient care.
