Equine Cushing's Syndrome, Part 2

Diagnostic Tools

• The most important diagnostic tool for identifying Cushing’s disease is the horse’s history and the clinical signs discussed in Part 1 of this series. A thorough physical exam may reveal some of the less obvious signs such as poor teeth and reproductive problems.

• Supporting lab work can be helpful and should be performed if possible, but may be inconclusive. Part of the problem is that in equine practice, single blood samples are taken whenever the practitioner is at the farm, so there is little standardization in the timing of the samples. Many of the parameters have daily variations and may change due to stress or other factors, including the amount of exercise a horse has had before the blood was drawn.

• Cortisol levels appear to be an inaccurate test for Cushing’s disease. Elevated blood cortisol can indicate high levels of stress in the body – but is the high cortisol coming from the Cushing’s, or has the Cushing’s come from the chronic stress caused by something like laminitis? High levels of cortisol suppress the immune system and contribute to more infections in these horses. Cortisol is the stress hormone, so both past and present stress are contributors.

• Resting insulin levels, ACTH, and glucose tests are sometimes used. The usual single-sample thyroid test does not give a true picture of thyroid function because there is significant variation in thyroid levels even in normal horses.

• The low dose dexamethasone suppression test (LDDS) is perhaps the most frequently used, but I would avoid it since dexamethasone is a steroid, and sensitive horses can get laminitis from steroids. I have seen a number of serious cases of laminitis in Cushing’s horses after steroid injections.

• Some new laboratory profiles are being offered that combine tests taken at various times of the day. These may be more accurate in positively diagnosing Cushing’s disease, although the tests often add little extra information to the clinical signs and basic blood tests.

• Also, have your veterinarian collect a complete blood count (CBC) to examine immune system status, and a chemistry screen to check organ function.

Insulin resistance

Cushing’s disease in horses has many of the same characteristics as insulin resistance. Many Cushing’s horses have elevated insulin levels in their blood. Normally, when a sugar or carbohydrate is eaten, blood sugar levels increase, insulin is secreted by the pancreas, glucose is carried into the cells by the insulin and the blood sugar goes back to normal. In insulin resistance, the cell walls are too stiff to let the insulin do its job properly. The glucose gets stored as fat instead of providing energy for the cells. Many horses store their fat in specific places, such as fat pads on their body and in the crests of their necks.

Holistic Treatment

Many tools in the alternative medicine toolbox can treat the Cushing’s horse, but each animal is an individual and will respond differently. In treating these complex cases, it is important to take it one step at a time and realize that the course of treatment may be long and expensive if the horse has many medical problems. There isn’t one simple answer. I try to look at how severe and longstanding the clinical signs are to determine how much to do at one time.

In many cases, homeopathy is important to the treatment’s success, but it is advisable to work with an experienced homeopath. Chinese medicine, both with acupuncture and herbs, can also be used to help Cushing’s horses. Again, it is best to work with a veterinarian experienced in these modalities.

Stay tuned for part 3 of this series coming next week!

Happy Riding!