Hyperthyroidism

29 Hyperthyroidism



David L. Panciera



1. What causes hyperthyroidism in the dog?

Hyperthyroidism in dogs is usually due to excessive thyroid hormone secretion by a thyroid tumor. Iatrogenic hyperthyroidism also occurs due to overdosing levothyroxine treatment. Thyroid tumors in dogs are usually malignant carcinomas and adenocarcinomas, and only 10% to 20% of the tumors are functional.


2. What are the clinical signs of canine hyperthyroidism?

Clinical signs of hyperthyroidism in the dog are similar to those of hyperthyroidism in the cat, including weight loss, polyphagia, polyuria/polydipsia (PU/PD), vomiting, diarrhea, behavioral changes, and panting. Many hyperthyroid dogs have a large ventral cervical mass and this is frequently noticed by the owner. Physical examination findings include an enlarged thyroid gland, thin body, muscle wasting, tachycardia, tachypnea, and difficulty swallowing or breathing due to local effects of the thyroid mass.


3. How is hyperthyroidism diagnosed?

A diagnosis of hyperthyroidism is confirmed by finding an elevated serum total T4 concentration in a dog with compatible clinical signs. Some dogs with autoimmune thyroiditis have T4 autoantibodies that cause false elevation of serum T4 concentration on the immunoassays used to measure T4. These dogs may be euthyroid or hypothyroid; hyperthyroidism does not occur as a result of T4 autoantibodies. If there is a question about T4 autoantibodies being the cause of an elevated serum T4 concentration, a test can be performed to detect the autoantibodies or serum free T4 (fT4) can be measured by equilibrium dialysis.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Hyperthyroidism

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