Hypothyroidism is an endocrine disease that is characterized by a deficiency of thyroid hormones. Commonly occurring in both dogs and humans, hypothyroidism causes a decreased metabolic rate and can lead to a multitude of systemic complications.
The Canine Thyroid Gland
In mammals, the thyroid gland is found in the neck area. The dog's thyroid is divided into two lobes that lie on either side of the trachea (windpipe) below the larynx (voice box).
The lobes look a bit like small deflated balloons, but they have a large role in regulating the body's metabolism. The pituitary gland regulates the production of thyroid hormones by producing and releasing thyroid stimulating hormone (TSH) as needed. Then, the thyroid gland produces thyroid hormones called T4 and T3 that are utilized throughout the entire body.
If the thyroid does not produce the needed amount of hormones, the metabolism slows and many of the body's normal processes are disrupted.
Hyperthyroidism (overactive thyroid) occurs in cats but is not typically seen in dogs. Unfortunately, an overactive thyroid in a dog is usually a sign of thyroid carcinoma, a cancerous thyroid tumor.
Causes of Hypothyroidism in Dogs
There are a number of potential causes of hypothyroidism in dogs, and the exact cause usually cannot be determined. Most commonly, canine hypothyroidism is immune-mediated.
Basically, the immune system attempts to destroy the thyroid, often resulting in atrophy of the gland. Some dogs are genetically predisposed to the disease, so this is something you can investigate if you know your dog's parents or littermates. Certain dog breeds are at a greater risk for hypothyroidism, such as Golden Retrievers, Irish Setters, and Cocker Spaniels.
Hypothyroidism can occur in a dog of any age, but it is most commonly seen in dogs from four to ten years of age. Gender does not appear to affect risk for hypothyroidism, but some evidence suggests that the disease can occur more commonly in spayed females than intact females. In rare cases, hypothyroidism may be congenital, meaning the disease was present at birth.
Be an advocate for your dog's health by visiting your veterinarian often and taking steps to keep your dog healthy. You may be able to help detect hypothyroidism before it becomes a serious heath problem.
Canine Hypothyroidism Symptoms
Canine hypothyroidism can manifest itself in a variety of ways, and the signs may be vague. Unfortunately, these symptoms can also indicate the presence of another disorder, so be sure to consult your vet if you notice any signs of illness. The most common symptoms of hypothyroidism include the following:
- Obesity/weight gain
- Hair loss on body and/or tail (rat tail appearance)
- Dull, dry hair coat
- Skin issues, such as infection or flaking
- Otitis (ear infection)
- Lethargy and/or weakness
- Behavioral changes
Less common but potentially serious complications of hypothyroidism include vestibular dysfunction (vertigo) and other neurological disorders, heart problems, and various health issues associated with obesity.
One or more of the above symptoms may occur in hypothyroid dogs, but even dogs with no symptoms can have the disease. For this reason, your dog should visit the vet for a wellness exam and routine blood work at least once or twice a year.