Hypothyroidism in Dogs

• Table of Contents
• Hypothyroidism in Dogs: Definition, Symptoms, and Treatment Process
• What is Hypothyroidism in Dogs?
• Causes of Hypothyroidism in Dogs
• How to Diagnose Hyperthyroidism in Dogs?
• How is Hypothyroidism in Dogs Diagnosed?
• Treatment of Hypothyroidism in Dogs
• What Should Be Done to Prevent Hypothyroidism in Dogs?
• Is Hypothyroidism in Dogs Transmissible to Humans?

Hypothyroidism in Dogs: Definition, Symptoms, and Treatment Process

Hypothyroidism in dogs is the term used to describe an endocrine disorder where the thyroid gland produces an insufficient amount of thyroid hormone. Hypothyroidism leads to a decrease in metabolic functions in dogs because thyroid hormones are essential for many cellular processes in the body.

What is Hypothyroidism in Dogs?

In dogs, the thyroid gland consists of two separate lobes located on either side of the trachea. Thyroid hormones play a significant role in metabolism and influence the function of many parts of the body. The most common cause of hypothyroidism in dogs is damage to the thyroid glands due to lymphocytic thyroiditis or idiopathic atrophy. These disorders can lead to the dysfunction of thyroid cells or the replacement of thyroid tissue with connective tissue.

Causes of Hypothyroidism in Dogs

In over 90% of dogs diagnosed with hypothyroidism, there is a condition called primary hypothyroidism, which can arise from two processes:

• Thyroiditis: This is the loss of healthy thyroid tissue due to the dog's immune system creating inflammation in the thyroid glands. The process can take months or even years and often has a hereditary origin.
• Atrophy: Fat and connective tissue replace the normal thyroid tissue. This can also be the final stage of thyroiditis.

There are other, much less common, reasons, generally including:

• Thyroid gland cancer
• Pituitary gland diseases
• Congenital defects
• External trauma

How to Diagnose Hyperthyroidism in Dogs?

Since thyroid hormones affect nearly every cell in the body, it is quite normal for dogs with hypothyroidism to exhibit multiple symptoms. Because the destruction of the thyroid gland progresses slowly, symptoms typically emerge gradually, making them prone to being overlooked. Common signs in dogs with hypothyroidism include:

• Weight Gain: Dogs with hypothyroidism experience weight gain due to a slow metabolism. Despite maintaining the same activity level, dogs gain weight.
• Energy Deficiency: Dogs may appear tired and lethargic. They tend to engage in less play or exercise.
• Skin and Coat Changes: Symptoms such as dry skin, flakiness, changes in color, and hair loss may occur.
• Sensitivity to Cold: Dogs can become more sensitive to cold weather conditions, with reduced resistance.
• Ear Infections and Other Skin Issues: Hypothyroid dogs commonly experience ear infections and skin infections.
• Slow Heart Rate: Hypothyroidism can lead to a decrease in the dog's heart rate.
• Muscular and Neurological Symptoms: Some dogs may exhibit muscle weakness, lack of coordination, or changes in their gait.

How is Hypothyroidism in Dogs Diagnosed?

Initially, veterinarians may resort to several tests to assess thyroid function based on the dog's history and observed symptoms. The commonly used diagnostic methods in case of observed symptoms are as follows:

• Clinical Signs and History: The veterinarian will evaluate typical symptoms for hypothyroidism. However, since these symptoms are not specific, additional tests are needed for a diagnosis.
• Basal Thyroid Hormone Test (T4): Usually, total T4 levels are measured as the first step. Low T4 levels strengthen the suspicion of hypothyroidism, but this condition could also be indicative of other disorders.
• Free T4 (fT4) Measurement: In addition to total T4, free T4 is considered a more specific test to diagnose hypothyroidism.
• Thyroid Stimulating Hormone (TSH) Test: Low T4 and high TSH levels are typical indicators of primary hypothyroidism. However, since TSH levels are not high in all hypothyroid dogs, this test should not be used alone.
• Thyroid Stimulating Hormone (TSH) Stimulation Test: This method is used for a more precise diagnosis. More costly and time-consuming than other tests, this test evaluates the capacity of TSH to stimulate the thyroid gland.
• Antibody Tests: Used to check for the presence of antibodies formed against the thyroid gland.
• In addition to these tests, T3, fT3, TRH, and TRH stimulation tests can also be used.

Changes compatible with hypothyroidism seen in only one of these tests are not sufficient to diagnose hypothyroidism. Test results need to be evaluated together. Hypothyroidism can progress in many different ways, and the interpretation of test results may vary depending on the patient.

Treatment of Hypothyroidism in Dogs

Hypothyroidism is an incurable but manageable condition. Dogs may need lifelong thyroid hormone replacement therapy. Control of hypothyroidism in dogs is usually successful, and with the right treatment and regular monitoring, most dogs can lead a normal life. Generally employed methods include the following:

• Levothyroxine (L-T4) Treatment: This is the primary treatment method for hypothyroid dogs. L-T4 is a synthetic form of thyroid hormone and is usually administered in oral tablet form. The dosage varies depending on the dog's weight, age, overall health, and any accompanying illnesses.
• Regular Monitoring: Serum T4 levels are checked a few weeks after starting treatment. If the process progresses positively, it is recommended to be monitored several times a year in response to treatment.
• Diet and Nutrition: In some dogs, a special diet that may assist in the treatment of hypothyroidism can be recommended. This situation can vary based on the individual needs of the dog.

What Should Be Done to Prevent Hypothyroidism in Dogs?

Hypothyroidism is a commonly encountered endocrine disease in dogs. While preventing all the causes of this disease may be challenging, the likelihood of its occurrence can be reduced by minimizing risk factors and taking certain precautions.

• Regular Veterinary Check-ups: Taking dogs to the veterinarian regularly is the key to early diagnosis. Especially in dogs above the average age, where the risk of hypothyroidism is higher, these check-ups should be more frequent.
• Balanced Nutrition: Inadequate iodine intake can be a cause of hypothyroidism. Therefore, it is important for dogs to be fed a balanced and complementary diet.
• Avoiding Exposure to Chemicals and Radiation: Some studies indicate that exposure to radiation and certain chemicals can cause thyroid dysfunction in dogs.
• Genetics: If a dog has a genetic predisposition to hypothyroidism, extra caution should be taken in breeding.
• Medications and Their Side Effects: It is known that some medications can trigger hypothyroidism. Therefore, you should consult your veterinarian about the medications prescribed for your dog and their potential side effects.

Is Hypothyroidism in Dogs Transmissible to Humans?

No, hypothyroidism in dogs does not transmit to humans. Hypothyroidism occurs when the thyroid gland cannot produce a sufficient amount of thyroid hormone. This condition can occur in both humans and dogs.