About Hypothyroidism

What is hypothyroidism?

Thyroid hormone is produced by the thyroid glands, small glands located in the neck. Thyroid hormone plays a very important role in regulating metabolism and the normal functioning of the body.

Hypothyroidism is a disorder in which the body produces too little thyroid hormone. It can be primary - due to disease of the thyroid glands - or secondary to other illnesses.

What are the clinical signs of hypothyroidism?

Skin changes include:

  • tragic facial expression, puffy face or dropping of the upper eyelids
  • increased shedding of hair
  • dry, coarse, thin or sparse coat
  • lack of hair regrowth, e.g. after clipping
  • dry and flaky skin (dandruff), that is not usually itchy
  • a rat tail
  • thickening of skin
  • darkening of the skin (hyperpigmentation), especially on the belly and the inner surface of the hind legs

Which dogs are more likely to be affected with hypothyroidism?

Virtually all breeds, including mixed breeds, can be affected by hypothyroidism. Dogs between 2 and 6 years of age are more commonly affected. Male and female dogs are affected in equal numbers.

How do dogs become hypothyroid?

Primary hypothyroidism in dogs is most commonly associated with destruction of the thyroid gland and a resultant deficiency in thyroid hormone in the blood stream. Two conditions are incriminated in over 95% of cases of primary hypothyroidism in dogs.

In lymphocytic thyroiditis, the body produces antibodies against the cells in the thyroid gland which destroy of the thyroid gland. Signs of hypothyroidism only develop after about 75% of the thyroid gland is destroyed. This process is slow, taking from 1-3 years to progress.

In idiopathic atrophy, cells of the thyroid gland are replaced by fat cells. The cause is unknown.

Primary hypothyroidism can also be secondary to a lack of another hormone, thyroid stimulating hormone (TSH), produced by the pituitary gland in the brain. This can be due to a congenital disorder (birth defect) or due to a brain (pituitary) tumor.

Top of page

Hypothyroid dogA tragic facial expression, puffy face and drooping eyelids seen in a dog diagnosed with hypotyroidism Source: Dr. Carmel Mooney

 

Subtle signs that can look like normal aging

  • lethargy, stiff and slow movements
  • lack of endurance
  • increased sleeping
  • reluctance to go for walks
  • tendency to gain weight
  • increased sensitivity to cold and seek warm places

Some of the commonly diagnosed breeds

  • Labrador retrievers
  • Golden retrievers
  • Doberman pinschers
  • Cocker spaniels
  • Boxers

Changes in the skin and hair coat are the most common reason for a hypothyroid dog to be is taken to see its veterinarian.