Hypothyroidism in Dogs: Causes & Symptoms
The thyroid gland is located at the base of your neck. It produces hormones which regulate metabolism, blood pressure, body temperature and many other functions. Thyroxin (T4) is responsible for regulating the amount of fat stored in your body, while T3 regulates the amount of sugar stored in your body.
When either hormone levels are too high or low they cause various symptoms such as weight gain, fatigue and depression.
There are two types of thyroid disease, primary and secondary. Primary thyroiditis occurs when the immune system attacks the thyroid gland itself. Secondary thyroiditis results from a combination of autoimmune disorders such as Hashimoto’s Thyroiditis, Goiter, Graves’ Disease and others.
These diseases all attack the pituitary gland causing it to produce abnormally large amounts of hormones which then go into overdrive resulting in hyperthyroidism.
Primary thyroiditis is usually caused by a virus, bacteria or parasite. The antibodies produced by these viruses and bacteria destroy the normal cells of the thyroid gland. If left untreated, this leads to death of the affected tissue.
Secondary thyroiditis is often due to a genetic mutation in one of the genes involved in producing thyroid hormones. A person with this condition will have no symptoms until their body begins to produce too much hormones which causes them to become depressed and lethargic. Antibodies will then be created as the immune response and this is where the second part of the name comes into play.
Hypothyroidism in dogs may also be caused by an under-active pituitary gland which stops it from producing enough thyroid stimulating hormone (TSH). This can result in a condition known as “central” hypothyroidism or decreased production of T4 or T3.
Normally, the thyroid gland produces two main hormones: triiodothyronine (T3), and thyroxine (T4). These hormones help control the amount of oxygen used in the body and the rate at which the body uses calories. In hypothyroidism, not enough T3 and T4 is produced leading to depression, weight gain and a low body temperature.
Dogs that suffer from end-stage kidney or liver disease may also experience hypothyroidism as a result of its treatment. If your dog has been diagnosed with either of the above conditions, it is important to have their thyroid function tests monitored. In some cases a change in diet or administration of medication may be enough to combat the disease.
Hypothyroidism in dogs can be treated through replacement of T4 (thyroxine) and T3 (liotrix). The most common cause of hypothyroidism in dogs is autoimmune thyroid disease.The immune system of an animal with this condition attacks the cells in the thyroid which produce hormones.
It can also be caused by a lack of iodine in the diet.
Even if you are not treating your pet with medication or a change in diet, it is important that they are tested regularly at least once per year. This is because a hypothyroid dog may display few obvious symptoms.
Sources & references used in this article:
- Neurologic dysfunction in hypothyroid, hyperlipidemic Labrador Retrievers (CL Vitale, NJ Olby – Journal of Veterinary Internal Medicine, 2007 – Wiley Online Library)
- Diagnosis and therapeutic management of hypothyroidism in a Labrador retriever dog (S Bhatt, PK Patel, BR Paul, NK Verma… – … of Entomology and …, 2018 – entomoljournal.com)
- Iatrogenic, sulfonamide‐induced hypothyroid crisis in a Labrador Retriever (K Brenner, K Harkin… – Australian veterinary …, 2009 – Wiley Online Library)