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Hypothyroidsim In Dogs

Education > Dog Health & Behaviour 1st April 2019

Hypothyroidism is a medical condition in which there is a low production of thyroid hormones. Thyroid hormones are produced by the thyroid glands (located in the neck on each side of the trachea) and play an important role in regulating metabolism. Common causes of hypothyroidism in dogs include immune-mediated destruction of the thyroid gland and natural atrophy of the gland. 

If the thyroid is overactive (hyperthyroidism - more common in cats), the body's metabolism is elevated. If it is underactive (hypothyroidism - more common in dogs), the metabolism slows down.

Clinical signs of hypothyroidism usually develop in middle aged or older dogs and include the following. On routine bloodwork, anaemia and increased lipid levels may be seen. 

  • loss or thinning of the fur coat
  • dry and dull skin with excessive shedding
  • weight gain without increase in appetite
  • lethargy and reduced activity
  • increased dark skin pigmentation

Breeds at higher risk of developing hypothyroidism include Golden Retrievers, Doberman Pinschers and Irish Setters. Hypothyroidism affects multiple other systems and therefore reproductive, neuromuscular, ocular, cardiovascular and gastrointestinal abnormalities are also possible, though less common. 

The suspicion of hypothyroidism is often based on history, clinical signs and changes in routine blood tests. An in-house total T4 test can be run to screen for hypothyroidism. This alone is not sufficient for the diagnosis of hypothyroidism as other factors such as non-thyroidal illnesses and medications can lead to the suppression of thyroid hormone production. Our vets may run other tests to rule out concurrent illnesses and a full thyroid panel is recommended to increase the accuracy of diagnosis. Some vets might prefer a trial therapy for the diagnosis of hypothyroidism. 

Treatment of hypothyroidism involves giving oral replacement of the thyroid hormone with synthetic T4 (Levothyroxine) for the rest of your dog's life. Dosing is usually started on a twice-daily basis. It is important to monitor response to therapy through a combination of clinical signs and regular blood tests, and make necessary adjustments to achieve the desired clinical response.

Dr Michelle Low
Mount Pleasant Animal Medical Centre (Bedok)