ACTH, adrenocorticotropic hormone, is produced by the pituitary gland. It’s function is to trigger cortisol release from the adrenal gland. Every year in the fall there is a temporary increase in the amount of ACTH produced. For most horses this is a relatively small increase and does not cause any problems. However, for horses in the early stages of PPID [pituitary pars intermedia dysfunction, aka Cushing’s Disease], it can mean disaster.
Autumn is dangerous for horses with undiagnosed early PPID
The classical and most obvious outward signs of PPID are muscle wasting, sagging abdomen and a long, often curly coat that does not shed normally. However, these develop relatively late in the course of the disease and PPID can be present for many years before they are seen.
Abnormally high ACTH levels are a laboratory marker of PPID but in early cases may be normal for most of the year. When the seasonal ACTH rise hits, these early PPID cases go into overdrive and generate levels much higher than the usual rise in healthy horses.
ACTH stimulates the adrenal gland to produce cortisol. Cortisol in turn causes insulin resistance. This can result in an unexpected case of laminitis, often the first of the horse’s life. Horses that already are EMS cases are at particularly high risk of developing insulin levels high enough to cause laminitis but it can happen to horses without a history of EMS too. An unexplained autumn laminitis is often the very first sign of PPID.
There are some other signs of an abnormally high ACTH rise. Look for:
- Sudden increased water consumption (often doubles)
- Increased urination
- Filling of the fossae above the eyes with fat
- Development of a fatty crest – or worsening if already there
The seasonal ACTH rise starts with minor increases that ramp up slowly starting end of June. The upward climb accelerates in September and peaks last week in September, with some minor variability depending on exact geographical location. Horses in the early stages of PPID experience exaggerated rises and problematic levels can be found as early as July in some horses.
If you see signs suggesting ACTH elevation may be excessive, call you veterinarian and do blood work to check. It may be suggested to start treatment with pergolide even before the blood results are in. Its important to understand the laminitis and other changes can only be controlled by removing the cause – the high ACTH. That is what the pergolide does. No amount of diet manipulation, supplements or anti-inflammatory drugs is going to make a difference if you don’t address the root cause.
If your horse is in his/her teens or older and develops unexplained laminitis in late summer/fall, be sure early PPID is on your list of possible causes and check ACTH. A correct diagnosis is the road to correct treatment.
Eleanor Kellon, VMD