Veterinarians commonly use intra-articular (injected into the joint) corticosteroids, such as triamcinolone acetonide (TA), to treat pain and inflammation in horses’ joints. Despite their popularity, corticosteroids can negatively impact the endocrine system, especially in horses with metabolic problems.

“Previous work by us and other scientists has shown a significant suppression of cortisol (a hormone involved in various metabolic processes) by TA,” said Allen Page, DVM, PhD, assistant professor in the Department of Veterinary Science at the University of Kentucky’s Gluck Equine Research Center, in Lexington. “Our research goal was to compare the metabolic effects of TA with those of autologous protein solution.” Horses diagnosed with insulin dysregulation (ID) and pituitary pars intermedia dysfunction (PPID, formerly known as equine Cushing’s disease) are at higher risk of developing laminitis after intra-articular corticosteroid injection, he said.

Triamcinolone acetonide is the most commonly used corticosteroid for injections in high-motion joints such as the fetlock. Autologous protein solution (APS) is a plasma product derived from a horse’s own blood used to reduce joint inflammation and promote healing. It delivers a concentrated solution of cells, platelets, growth factors, anti-inflammatories, etc. to the target location.

Page and his fellow researchers tested the effects of fetlock joint injections using a rotation of either a saline solution (the placebo, having no therapeutic effect), followed by APS or 9 milligrams of TA on five geldings for three consecutive treatment blocks lasting 28 days each. At different time intervals post-treatment, they collected plasma and serum samples of adrenocorticotropic hormone (ACTH, a hormone the pituitary gland produces that stimulates cortisol release), cortisol, glucose, insulin, thyroid hormone, and thyrotropin-releasing hormone and performed oral sugar tests.

The Metabolic Effects of Corticosteroids vs. APS

“A single 9-mg dose of TA had a significant effect on both the oral sugar test and the TRH test,” said Page. An oral sugar test measures a horse’s insulin response to sugar intake, and a TRH test assesses how well the pituitary gland, a gland in the brain that makes, stores, and releases hormones, responds to TRH. “Both are common tests for ID and PPID, respectively. This effect was seen at two days post-TA administration, which suggests we need to be careful of the timing of these tests when also potentially treating joint disease with TA.”

The researchers also found that intra-articular TA administration led to significant ACTH and cortisol suppression for 96 hours post-treatment. In addition, after TA treatment, blood glucose and insulin levels increased between 12 and 48 hours, and for 32 hours, respectively. “The concern is the potential for hyperinsulinemia-associated laminitis, which is one of the main considerations with ID horses,” Page said.

Therefore, he noted that choosing APS over TA has one major benefit: “By administering APS, we avoid the metabolic effects on ACTH, cortisol, glucose, and insulin levels, which should be a consideration when treating joint disease in ID horses.”

However, he and his colleagues tested intra-articular TA and APS only on metabolically normal horses, so further trials in ID horses are needed to conclusively determine the effects in those animals.

Take-Home Message

“Our findings reminded me that intra-articular TA is not as innocuous as we may think it is,” Page said. Therefore, he recommended veterinarians always consider and assess the drug’s potential metabolic effects on equine patients before administration.