Etio-pathogenesis and epidemiology of Hypothyroidism

DEFINITION ETIO-PATHOGENESIS AND EPIDEMIOLOGY OF HYPOTHYROIDISM

Definition

  • Hypothyroidism is the result of decreased production of thyroxine (T4) and Triiodothyronine (T3) by the thyroid gland.

Etio-pathogenesis

  • Hypothyroidism may result from dysfunction of any part of the hypothalamic – pituitary – thyroid axis.
  • Primary acquired canine hypothyroidism is due to lymphocytic thyroiditis.
  • In idiopathic follicular atropy, there is loss of thyroid parenchyma and replacement by adipose connective tissue.
  • Less commonly, hypothyroidism is caused by bilateral thyroid neoplasia.
  • Secondary hypothyroidism (deficiency of TSH) is rarely described in dogs. Causes of acquired secondary hypothyroidism include pituitary malformations and pituitary neoplasia.
  • Tertiary Hypothyroidism (deficiency of TRH) is yet to be documented in the dog.
  • Congenital hypothyroidism (cretinism) is rarely diagnosed in dogs.
  • Congenital primary hypothyroidism includes iodine deficiency, thyroid dysgenesis and dyshormonogenesis.
  • Secondary congenital hypothyroidism due to apparent isolated TSH or TRH deficiency was reported in a family of young giant schnangers and in a young boxer.
  • Iatrogenic causes of hypothyroidism include iodine treatment, administration of anti-thyroid drugs and surgical thyroidectomy.

Epidemiology

  • The reported prevalence of canine hypothyroidism is from 0.2% to 0.8%. Mean age at diagnosis is 7 years, with range of 0.5 to 15 years. Golden retrievers and Doberman pinschers are among the breeds reported to be at higher risk for hypothyroidism.
  • In one study, Neutered males and females were reported to be at increased risk for developing hypothyroidism compared with sexually intact animals.
Last modified: Friday, 20 January 2012, 7:13 AM