Hypothyroidism/Dogs

The thyroid gland is a butterfly shaped gland the lies on either side of the trachea (windpipe) and is vital in your pet’s metabolic function. Hypothyroidism is the underproduction of thyroid hormone and thus a slow metabolic function. Hypothyroidism is a common endocrine disease in dogs, typically affecting those around 6-7 years old. It is more prevalent in spayed females and neutered males and can affect various breeds.

Causes:

In dogs, hypothyroidism is typically caused by one of two conditions: lymphocytic thyroiditis or idiopathic (unknown reason) thyroid gland atrophy. Lymphocytic thyroiditis is the most prevalent cause of hypothyroidism and is considered an immune-mediated condition, where the immune system identifies the thyroid as abnormal or foreign and attacks it. The exact cause of this reaction is unknown; however, it is a heritable trait, indicating a genetic component. In idiopathic thyroid gland atrophy, normal thyroid tissue is replaced by fat tissue. This condition is also not well understood.

When the thyroid gland is affected, most every bodily function will be affected. Here is a list of some general clinical signs that may be seen in a dog affected by hypothyroidism.

• Weight gain without increased appetite 
• Lethargy and lack of exercise desire
• Cold intolerance
• Dry, dull hair with excessive shedding or baldness
  • Hair doesn't regrow after clipping
• Dark skin pigmentation
• Frequent skin and ear infections
• High cholesterol
• Slow heart rate

Other possible symptoms:

• Thickened facial skin giving a “tragic” expression
• Nerve issues causing lameness, foot dragging, lack of coordination, head tilt
• Loss of libido and infertility in males
• Lack of heat periods, infertility, miscarriage in females
• Fat deposits in eye corneas
• Dry eye due to improper tear production (KCS)

Evaluation/Diagnosis:

Your primary care veterinarian will likely want to run a total thyroxine (T4) to determine if your cat is hyperthyroid. If your dog has a TT4 level in the lower normal range, a second test like free T4 by equilibrium dialysis (FT4 by ED) can be done.

 Treatment:

Treatment for hypothyroidism consists of replacing thyroid hormone by medication (life-long). Typically, your veterinarian will start at a standard dose per your dog’s weight and recheck your dog’s T4 in one month 4-6 post-pill administration as thyroid hormones can fluctuate. Medication adjustments may need to be made from time to time and blood monitoring will likely be checked every 6-12 months.