Hemithyroidectomy in a horse with confirmed hyperthyroidism.

This research focuses on the successful treatment of a 23-year-old Quarter Horse diagnosed with hyperthyroidism. The hyperactivity was treated through hemithyroidectomy (partial removal of the thyroid gland).

Background

A Quarter Horse gelding, characterized by cachexia (wasting syndrome) and heightened activity for a year, was brought to the hospital. The horse’s symptoms included severe emaciation, fast heart rate, a pronounced diastolic murmur, fever, excessive thirst, inward-bulging eyeballs, and loss of hair. The horse also exhibited hyper excitability and insatiable hunger. The right lobe of the horse’s thyroid gland was visibly enlarged. Hyperthyroidism was the presumptive diagnosis based on the clinical signs and high plasma thyroid hormone levels.

Diagnosis

The horse was confirmed with hyperthyroidism using the results from a triiodothyronine-suppression test. Triiodothyronine is a thyroid hormone; hyperthyroidism patients usually fail to show a decrease in their hormone levels during this test. Post endocrine testing the diseased part of the thyroid gland was extracted:

• Identified histologically as an adenoma. An adenoma is a benign tumor that originates from glandular epithelium.

Treatment and Conclusion

After the hemithyroidectomy (partial removal of the thyroid gland):

• The horse’s plasma thyroid hormone levels returned to normal range values.
• The clinical signs of the disease resolved, confirming the initial hyperthyroidism diagnosis.

This case indicated that in horses with hyperthyroidism, hemithyroidectomy appears to be a successful treatment.