Need clarification on all the terms used to talk about your horses' metabolic problems? We are here to help!

As more is researched and understood about metabolic disorders and insulin-related issues in horses, the terminology is constantly changing and evolving, which can lead to confusion. Terms like "insulin resistance (IR)," "hyperinsulinemia," "equine metabolic syndrome (EMS)," and "insulin dysregulation (ID)" often appear interchangeably in the literature, leading to misunderstandings about diagnosis, treatment, and management. Here's a short discussion about navigating these ailments and terms to clarify their distinctions and interrelations.

 Reference: 

Frank, Nicholas, et al. “Recommendations for the Diagnosis and Management of Equine Metabolic Syndrome (EMS).” Equine Endocrinology Group, Tufts University, June 2022, sites.tufts.edu/equineendogroup/files/2022/10/EMS-EEG-Recommendations-2022.pdf.

What is Insulin Resistance (IR)?

Traditionally, "insulin resistance" has been widely used to describe a condition where the body's cells fail to respond adequately to insulin. In horses, it's often associated with overweight or obese individuals and can predispose them to various metabolic disorders. However, IR focuses narrowly on the cellular insulin response, not encompassing the full spectrum of insulin-related abnormalities.

What is Hyperinsulinemia?

Hyperinsulinemia refers to elevated insulin levels in the blood and can result from or contribute to insulin resistance. It's a direct marker of how the horse's body is managing insulin and glucose, but on its own, it doesn't provide a complete picture of metabolic health. This term is specific but doesn't account for the cause or the body's response to glucose intake.

What is Equine Metabolic Syndrome (EMS)?

EMS is a broader term that describes a cluster of symptoms, including insulin dysregulation, obesity, and a predisposition to laminitis. While it encompasses insulin-related issues, it also implicates a broader range of metabolic dysfunctions. The challenge with EMS is that it's a syndrome, not a specific disease, which means it's diagnosed based on a collection of clinical signs rather than a single diagnostic test.

What is Insulin Dysregulation (ID)?

"Insulin Dysregulation" is a comprehensive term that includes hyperinsulinemia, insulin resistance, and an abnormal response to oral or intravenous glucose. Many equine professionals currently favor it because it accurately captures the complexity of insulin's role in equine metabolic health. ID encompasses a range of dysfunctions, from the body's production of insulin, its response to insulin, and the regulation of blood glucose levels. This term serves as an umbrella, highlighting that insulin-related issues in horses are multifaceted and interconnected. Now considered the correct terminology to describe the disorder, this term is becoming more commonly used among veterinarians.

What is Cushing's Disease or Pituitary Pars Intermedia Dysfunction? (PPID): 

Although sometimes lumped together with EMS, PPID is a distinct condition caused by an enlargement of the pituitary gland, leading to an overproduction of certain hormones. Symptoms include:

• Increased thirst and urination.
• Loss of muscle mass.
• A long, curly coat that fails to shed properly.

Not every horse with the disease will have all the classic symptoms. In the early stages of PPID, the signs can be much more subtle than the classic symptoms seen with late-stage PPID. While PPID can share some clinical signs with EMS, such as a predisposition to laminitis, they are different conditions with different underlying causes. A blood test is needed to diagnose a horse with PPID accurately.

Is Laminitis a Metabolic Disease?

While laminitis is often associated with metabolic issues, it is not a disease. Laminitis involves inflammation of the sensitive laminae within the hoof and can be extremely painful, leading to lameness and, in some cases, euthanasia. Laminitis can result from mechanical stress, systemic infections, fevers, elevated insulin levels, and certain medications.

How is Obesity related to Metabolic Disorders in horses? 

Obesity is a risk factor for EMS but is not a metabolic disorder in itself. However, excessive body weight can exacerbate insulin dysregulation and increase the risk of laminitis, making it a critical factor in managing horses with metabolic disorders. Not all horses with ID or PPID are overweight, but it indicates that testing may be warranted. Horses with abnormal fat deposition, or fat pads, are at a higher risk of having EMS.

Navigating the Terminology

While the varied terminology can be confusing, each term provides valuable insights into equine metabolic health. A clear understanding of the different terms and distinct disorders enhances communication between owners and veterinary professionals, leading to better diagnosis, management, and care strategies for affected horses. There is a significant overlap with these ailments; ensuring a proper diagnosis with a tailored management plan through medication, diet, and supplementation can improve the affected horse's life.

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Written in collaboration with Dr. Megan Knoell, Mobile Veterinarian Expert Care in NY's Orange, Sullivan, Westchester, Ulster & NJ | Knoellwood Equine

Resources for further reading: 
https://esc.rutgers.edu/fact_sheet/metabolic-problems-in-the-horse-sorting-out-the-diagnosis/

https://thehorse.com/1109648/understanding-equine-endocrine-disorders/