Cardiac Disease Related to Primary Hyperthyroidism in a 20-Year-Old Mule.
Authors: Brown Kaitlin, Williams Louie Elizabeth, Pinn-Woodcock Toby, Pearson Erin, Pearson Garett B, Marr Jacqueline, Hackett Eileen S, Rath Brown Laura, Mitchell Katharyn J
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Cardiac Disease and Primary Hyperthyroidism in Equids Primary hyperthyroidism remains exceptionally rare in equines, and this 2024 case report documents the first documented instance of clinically significant cardiac remodelling secondary to the condition in the species. A 20-year-old mule presenting with three months of weight loss despite increased appetite, persistent tachycardia and a pansystolic heart murmur underwent comprehensive investigation including thyroid hormone assays, echocardiography and thyroidectomy; histopathology revealed adenocarcinoma of the left thyroid with adenomas in the right lobe. The case demonstrated marked elevation in free T4, total T4 and T3 concentrations alongside left ventricular concentric hypertrophy with enhanced systolic function—a direct cardiac consequence of excessive thyroid hormone exposure. Following bilateral thyroidectomy and subsequent levothyroxine supplementation (necessitated by post-operative hypothyroidism), the mule's polyphagia resolved and weight gain resumed, though echocardiographic changes persisted at two-year follow-up, suggesting incomplete reversal of thyroid hormone-induced cardiac remodelling. For equine practitioners, this case underscores the importance of measuring thyroid function in geriatric equids presenting with weight loss, tachycardia and cardiac murmurs, as early identification may prevent irreversible structural changes, and highlights that even successful surgical management may not fully normalise cardiac function once significant remodelling has occurred.
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Practical Takeaways
- •Hyperthyroidism should be considered as a differential diagnosis in equids presenting with weight loss despite increased appetite, tachycardia, and cardiac murmurs; thyroid hormone concentrations should be measured in such cases.
- •Hyperthyroidism can cause hemodynamically significant cardiac remodeling in equids; echocardiographic monitoring is warranted in hyperthyroid patients to assess for left ventricular hypertrophy.
- •Bilateral thyroidectomy is a viable treatment option for equine hyperthyroidism and can be performed under standing sedation, though lifelong thyroid hormone supplementation monitoring is necessary post-operatively.
Key Findings
- •A 20-year-old mule with primary hyperthyroidism presented with markedly elevated free T4, total T4, and T3 concentrations, representing the first documented case in equids.
- •Echocardiography revealed left ventricular concentric hypertrophy with increased ventricular and atrial systolic function secondary to hyperthyroidism.
- •Histopathology confirmed thyroid adenocarcinoma in the left gland and multiple adenomas with osseous metaplasia in the right gland.
- •Bilateral thyroidectomy was performed successfully under standing sedation, with post-operative levothyroxine supplementation required after undetectable thyroid hormone concentrations were documented.