In the last newsletter, we talked about seasonal rhythms and how important hormones and signaling molecules can change with the seasons. (Available here)
After writing the newsletter, I was asked, “Are elevated levels of ACTH always indicative of Cushing’s Disease?” (Cushing’s Disease is also known as PPID) The short answer is no.
◆︎ What causes elevated ACTH?
A pituitary adenoma. This is a non-cancerous focal pituitary enlargement and proliferation of cells that spew out regulatory hormones. Although we measure ACTH levels, there are many other regulatory hormones that are also released. This is usually the intermediate lobe, but may be the anterior lobe.
◆︎ Why is it important to be aware of elevations in ACTH?
Elevated ACTH levels that are caused by a pituitary adenoma, can be a driver of high insulin levels. High insulin is associated with laminitis. We care about high ACTH, not because we are concerned that the horse has a shaggy coat. We care about it because we want to avoid laminitis. Despite our advances in understanding laminitis, it is still a major reason why we euthanize our horses.
◆︎ What are some of the signs that our horse may have elevated ACTH?
» Laminitis
» Weight loss
» Lethargy
» Muscle wasting
» Coat changes, delayed shedding
» Sweating irregularities – anhidrosis, or patchy sweating
» Uncontrollable allergies
» Increased susceptibility to infection
» Barren mares with enlarged mammary glands and/or lactating
» Polyuria/polydypsia (excessive urination, excessive drinking)
◆︎ What can cause an elevated ACTH?
➡ Season: During the fall, ACTH numbers tend to rise. In young horses, they easily handle the rise. In younger horses, an increase in ACTH numbers does NOT necessarily mean that your horse has PPID.
However, in older horses, ACTH starts rising sooner, rises higher, and lasts longer. This CAN mean that your horse has PPID.
➡ Age: Older horses can have elevated ACTH levels even during the times of year that the ACTH numbers should be lowest, such as March or April.
➡ Trailering: It is not recommended to trailer your horse to the vet for a blood to test ACTH levels. The trailer ride most likely will cause the ACTH levels to rise. This is NOT necessarily PPID.
➡ Pain: Horses in pain will also have an elevated ACTH level. This is due to the stress caused by pain. This elevation is NOT necessarily PPID.
➡ Geographic location: During the seasonal rise, the ACTH levels are also dependent on the geographic location.
➡ Breed: Shetland and Welsh ponies tend to have higher ACTH levels than larger breeds.
◆︎ Common tests to diagnose elevated ACTH:
➡ ACTH test: This consists of a single blood draw that is sent to the lab. The ACTH value can be compared against known cyclical patterns to determine if an elevated ACTH is higher than what you would expect.
➡ TRH-stimulation test: If an ACTH come back with equivocal results, a TRH-stim test can be performed for greater accuracy in diagnosis of PPID.
Dexamethasone suppression test is NOT recommended due to the potential for the test to induce laminitis.
◆︎ Treatment:
There are several therapies available to treat elevated ACTH. These treatments need to be prescribed by your veterinarian.
» Prascend® is an FDA approved form of pergolide, by Boehringer™, available in 1 mg tablets.
» Compounded pergolide through a compounding pharmacy
» Cabergoline – a newer treatment, sometimes used when the ACTH is not controlled by pergolide
Supplements:
» Chastetree berry is a supplement that is sometimes used to control the symptoms of elevated ACTH. However, studies have shown that while it may reduce symptoms, it does not lower the ACTH levels.
◆︎ Why treat?
The reason for treating elevated ACTH is to avoid laminitis. Additionally, if there is muscle wasting, weight loss, or chronic infections, these conditions most likely will not resolve without addressing the underlying ACTH level.
We do the best we can for our horses. Being aware of the ACTH level is part of that.
Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay 2024