UNIVERSITY OF CALIFORNIA, DAVIS



UNIVERSITY OF CALIFORNIA, DAVIS

VETERINARY MEDICAL TEACHING HOSPITAL

SCHOOL OF VETERINARY MEDICINE

DAVIS, CA 95616

SMALL ANIMAL CLINIC 530-752-1393

DERMATOLOGY SERVICE

Information for Clients

Hypothyroidism

Introduction

Hypothyroidism or “low/underactive thyroid” is due to an impaired production or secretion of thyroid hormone by the thyroid gland. Greater than 95% of true primary hypothyroidism cases result from inadequate functioning or destruction of the thyroid gland itself. The cause(s) behind this are unknown or poorly understood. There is strong evidence of a predisposition for certain breeds of dogs to develop hypothyroidism. The Golden Retriever, Doberman Pinscher, Irish Setter, Boxer Dog, Miniature Schnauzer, Dachshund and Poodle are all predisposed. Mixed breed dogs may also be affected. Age of onset is usually middle aged, 4-7 years old. Dogs under the age of 2 years are rarely affected.

Clinical Signs

The clinical signs of hypothyroidism are subtle and progressive. As the thyroid hormone directly affects metabolism, metabolic changes can be observed. Lessened activity, exercise intolerance, weight gain (without increase in appetite or food consumption), and intolerance to cold have all been noted. Patients may have some, all or none of these signs. Dermatologic changes are often the first noted. Hair loss or changes in hair coat quality are common. The hair coat may become coarse or dull and some scaling of the skin may be observed. Usually, these changes occur over the trunk or body of the patient. Some patients will acquire a hairless “rat tail” (usually much to their person’s dismay!). Hypothyroidism, as with some other hormonal disorders, generally spares the head and the extremities (legs and feet). The skin in the hairless areas may become thickened and hyperpigmented. Dogs suffering from hypothyroidism are also more prone to recurrent secondary skin and ear infections.

Diagnosis and Treatment

Hypothyroidism is diagnosed with blood tests, which measure the levels of the various thyroid and thyroid stimulating hormones. Certain medications or concurrent systemic illness can decrease thyroid values. In these situations, the thyroid values should normalize once the medication is discontinued or the illness resolved. In the event of low thyroid values in these situations, or if thyroid values are “borderline”, then it is recommended that the test be repeated in 1-3 months for reevaluation. Treatment for hypothyroidism is relatively simple and inexpensive. An oral tablet, containing synthetic thyroid hormone, is given twice daily for the first 4-6 weeks. At that time a “post pill” thyroid blood test is done to check the thyroid level while the dog is receiving medication. Depending on the result, the medication dosage is adjusted and the medication is continued either once or twice daily. Thyroid treatment is usually life long, and thyroid values should be rechecked every 12 months to adjust medication accordingly. Overall improvement in energy level, weight loss and attitude should be seen in the first 4-6 weeks. It may take longer for the skin and hair coat to normalize.

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