Veterinarian Column: Hypothyroidism in dogs

by Alice's Dog & Cat獣医師

Alice’s Dog&Cat Veterinarian Column

Hypothyroidism is a common disease in dogs. Various symptoms such as repeated skin diseases, otitis externa, and obesity are observed due to insufficient secretion of thyroid hormone. Hypothyroidism may be overlooked because it is not an urgent, life-threatening condition. Because hypothyroidism is hidden, the disease may not be cured easily or may recur easily. This time we will explain hypothyroidism in detail.


Hypothyroidism is often caused by lesions in the thyroid gland, but in rare cases, abnormalities in the pituitary gland or hypothalamus can cause hypothyroidism.

Lesions present in the thyroid gland

・Lymphocytic thyroiditis

・Idiopathic thyroid atrophy

・Thyroid tumor


Causes other than thyroid

・Pituitary gland and hypothalamic abnormalities

Alice's Dog&Cat Veterinarian Column Hypothyroidism in Dogs


A variety of symptoms occur due to insufficient secretion of thyroid hormones.

・Hair removal (symmetrical hair loss, nose bridge hair loss, tail hair loss)


・Recurrent pyoderma

·otitis externa


-Slow pulse

・Decrease in activity

・Abnormalities in blood tests (hypercholesterolemia, hypertriglyceridemia, anemia, increased ALP )


・Facial nerve paralysis


・Vestibular disorders

・Hypothermia, feeling cold

Alice's Dog&Cat Veterinarian Column Hypothyroidism in Dogs


Diagnosis is made by combining clinical symptoms and the following tests.

Thyroid function test: Measures thyroid hormones T₄ , (thyroxine), fT₄ (free thyroxine), and TSH (thyroid stimulating hormone). In cases of hypothyroidism, T ₄ and fT ₄ are often reduced. TSH is often increased, but sometimes no abnormality is seen.

Ultrasound test: Check for thyroid abnormalities.

*Yuthyrodosic syndrome

Euthyrodosic syndrome is a phenomenon in which thyroid hormone levels decrease due to severe diseases other than the thyroid gland or medication. To avoid misdiagnosis of hypothyroidism, it is necessary to measure and diagnose thyroid hormone again after treatment of the disease.

Causes of decreased thyroid hormone

・Medications (prednisolone, phenobarbital, non-steroidal anti-inflammatory drugs, etc.)

・Anesthesia and surgery

・Severe systemic disease

Alice's Dog&Cat Veterinarian Column Hypothyroidism in Dogs


Administer a thyroid hormone drug called levothyroxine sodium.

After starting treatment, check for improvement in symptoms and measure T₄ to confirm that the dosage is appropriate.

Improvement in decreased activity often occurs within one week of starting treatment, and hyperlipidemia often improves within a few weeks. It may take several months for skin symptoms to improve. Hypothyroidism requires lifelong medication.

Some pet owners assume that symptoms of hypothyroidism (such as decreased thyroid activity, recurrent obesity or skin problems) are due to their dog getting older. Hypothyroidism is a disease that progresses well if treated. If your dog exhibits symptoms consistent with hypothyroidism, we recommend that you have your dog undergo a thyroid function test at a veterinary hospital rather than assuming that it is due to age.