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The thyroid is the most important endocrine gland in regulating the body's basic metabolism. It is located in the neck, near the trachea in all animals. It produces hormones such as thyroxine (or T4), which regulate metabolism, body temperature, heart rate, growth, weight and energy levels, among other things. The thyroid gland is under the control of thyrotropin (or TSH), produced by the pituitary gland, which stimulates the synthesis of thyroid hormones. TSH in turn is controlled by thyrotropic hormone (or TRH), produced by the hypothalamus. Thyroid hormones then exert a negative feedback loop on the pituitary gland and hypothalamus, creating a balance and meeting the body's needs. When this feedback loop and its balance are broken or disturbed, this is when certain thyroid diseases and imbalances appear.
The most common thyroid disease in dogs is hypothyroidism. This is a condition caused by an underactive thyroid gland, which generally affects senior dogs. The causes of this underactivity are linked to progressive destruction of the gland by autoimmune disease or idiopathic thyroid atrophy. This thyroid disease usually presents itself in the form of various symptoms: weight gain without increased appetite, lethargy, fatigue, cold intolerance, hair loss, dull coat, frequent skin infections, slow heartbeat or any combination of these. Treatment for this condition is relatively simple, but requires a great deal of discipline and diligence. The owner will need to administer daily medication designed to replace thyroid hormones (e.g. levothyroxine) for the rest of the animal's life.
When it comes to our feline friends, the most frequently encountered thyroid disease is hyperthyroidism, a condition defined by an overactive thyroid. This disease is most often found in older cats, generally aged 10 and over. The gland's overactivity may be due to benign hyperplasia (an enlargement of the gland), or sometimes to a benign tumor (an adenoma). Hyperthyroidism manifests itself in various ways: weight loss despite a healthy appetite, hyperactivity, vomiting, diarrhea, elevated heart rate, increased thirst and urination, a dull coat, or any combination of these. Again, treatment remains uncomplicated, involving the administration of oral or transdermal antithyroid medication (e.g. methimazole) that reduces thyroid hormone production. Other options for owners of hyperthyroid pets include a specialized diet low in iodine, a chemical element essential for thyroid hormone synthesis. Radioactive iodine treatment, a curative solution where the animal is cured of its hyperthyroidism, is also a feasible option, if owners' financial means allow.
To diagnose hypo- or hyperthyroidism in any animal species, it's important to take a blood sample to measure T4 and TSH levels. A clinical examination supplemented by a detailed history will establish your pet's thyroid profile. If you observe one or more of the above symptoms, book a virtual consultation with a Neovet veterinarian. He or she can assess the situation, discuss the signs observed and, if necessary, prescribe a blood test at one of our partner clinics, or schedule a home visit with an Animal Health Technician (AHT) in the areas we serve.
