First signs of Cushing's disease (PPID) in horses

What it looks like

• •A coat that sheds late, sheds patchily, or stops shedding altogether, and hair that grows long and curly (hypertrichosis)
• •Loss of muscle over the topline and rump, sometimes with a pot-bellied or pendulous abdomen
• •Weight loss despite an unchanged ration
• •Drinking and urinating noticeably more than usual
• •Lethargy, somnolence, or a drop in willingness to work
• •Sweating more, or in patches, or sweating less than the horse used to
• •Repeated infections, slow-healing wounds, or recurrent hoof abscesses
• •Swelling of the hollow above the eye (the periorbital fossa)
• •Laminitis, especially recurring laminitis with no diet accident to explain it

Likely causes, ranked

A tag marks the causes that are pain wearing a behavior label. Those are the ones to rule out first.

1. 01PPID itself: loss of dopamine control over the pituitarycommonpossible painThe University of Illinois describes the degeneration of the neurons that produce dopamine, which leaves the horse unable to control the hormones made by the middle lobe of the pituitary gland. Merck adds that pituitary adenomas compress the hypothalamus and secrete increased alpha-melanocyte-stimulating hormone, a factor in the growth of a long winter coat. It is a progressive disease of older horses that is managed, not cured.
2. 02Insulin dysregulation alongside PPIDcommonpossible painMerck states that if insulin dysregulation is also present, horses with PPID are at high risk for laminitis. Illinois makes the same point: horses with concurrent insulin dysregulation or equine metabolic syndrome face an increased risk of laminitis. This is why a vet who suspects PPID will usually check insulin as well as ACTH, and why sore feet in an older horse is a reason to test.
3. 03Equine metabolic syndrome on its ownpossiblepossible painColorado State University notes that PPID overlaps significantly with equine metabolic syndrome and that some horses have both at once. EMS produces regional fat pads, a cresty neck and laminitis risk without the coat and muscle changes of PPID, so the two are told apart on testing, not on appearance.
4. 04Normal aging, dental disease, or parasitespossiblepossible painMuscle loss over the topline and weight loss are not specific to PPID. Iowa State University Extension notes that aged horses lose condition and topline muscle partly because they process protein less efficiently, and dental disease and parasite burden cause the same picture. These are ruled in or out at the same visit, which is why a vet exam beats a guess from a photograph.
5. 05Another chronic diseaseless commonpossible painLethargy, weight loss and repeated infections are the shared language of many chronic conditions, not only PPID. A blood panel taken with the ACTH sample is how the vet separates a horse with PPID from a horse with liver, kidney, or another systemic problem presenting the same way.

What to try

1. 1Write down what has changed, and whenNote the date the coat should have shed and did not, any drop in topline, the water bucket going down faster, and every abscess or infection in the past year. PPID is progressive and the early signs are gradual, so a written timeline is more useful to the vet than an impression.
2. 2Ask the vet for an ACTH testMerck states that definitive diagnosis of PPID is based on evocative testing or measurement of resting endogenous ACTH concentrations, and Illinois describes the blood test for ACTH as the diagnostic. Colorado State adds the TRH stimulation test, where a baseline sample is taken, TRH is given intravenously, and ACTH is measured again ten minutes later.
3. 3Know that autumn results need interpretingColorado State notes a normal seasonal elevation of ACTH in the fall and early winter that can make it difficult to definitively diagnose PPID during this time. That does not mean you wait: it means the vet interprets the number against the season rather than against a single year-round cut-off.
4. 4Have insulin checked at the same timeMerck's line is that horses with PPID are at high risk for laminitis if insulin dysregulation is also present. Testing both at one visit tells you whether this is a horse that needs its feet and its sugar intake watched closely, or a horse whose main problem is the coat and the muscle.
5. 5Treat and then manage, for lifeMerck names pergolide, a dopaminergic receptor agonist, as currently the only agent demonstrated to decrease endogenous ACTH concentrations in horses with PPID, at a starting dose of 2 micrograms per kilogram by mouth every 24 hours. Illinois pairs the daily pergolide with diet management, dental and hoof care, deworming, body clipping, pelleted feeds, grazing muzzles and limited pasture. There is no cure, so this continues for the life of the horse.

Questions people ask

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Sources

Every figure on this page traces to one of these. We cite registries, associations, government and veterinary bodies, and published cost surveys - not other blogs.

1. [1]Pituitary Pars Intermedia Dysfunction (PPID) in Horses- University of Illinois College of Veterinary MedicinegovThe presenting signs of PPID (hypertrichosis, poor hair coat, muscle atrophy, weight loss, susceptibility to infections, lethargy), that PPID commonly affects horses and ponies aged 15 and older with Morgans and ponies predisposed, that it affects up to one-fourth of horses, the ACTH blood test, the loss of dopamine-producing neurons, daily oral pergolide plus diet, dental, hoof and grazing management, and the increased laminitis risk when insulin dysregulation or EMS is present.
2. [2]Hypertrichosis Associated With Adenomas of the Pars Intermedia in Horses- Merck Veterinary ManualeditorialThat hypertrichosis is excessive growth of the nonshedding coat in older horses, typically 18 years or older, the additional common signs (polyuria and polydipsia, poor muscle tone, weakness, somnolence, abnormal fat distribution, periorbital fossa swelling, increased susceptibility to infections, intermittent pyrexia, generalized hyperhidrosis), that pituitary adenomas compress the hypothalamus and increase alpha-MSH, that definitive diagnosis rests on evocative testing or resting endogenous ACTH, that pergolide at 2 mcg/kg orally every 24 hours is currently the only agent shown to lower endogenous ACTH, and that horses with PPID are at high risk for laminitis if insulin dysregulation is also present.
3. [3]Equine Cushing's Disease- Colorado State University Veterinary Health SystemgovThat the disease affects middle-aged to geriatric horses with most cases over 15 years of age and is rarely reported in younger animals, the clinical signs including hypertrichosis, weight loss and muscle wasting, laminitis, excessive drinking and urination, delayed wound healing and recurrent hoof abscesses, the overlap with equine metabolic syndrome, the TRH stimulation test protocol with ACTH measured ten minutes after TRH, the normal seasonal elevation of ACTH in fall and early winter, and once-daily oral pergolide as the standard treatment.
4. [4]Laminitis in Horses- Merck Veterinary ManualeditorialThat endocrine dysfunction, covering equine metabolic syndrome and PPID, is probably the most common underlying cause of laminitis in horses today, with hyperinsulinemia thought to be the predisposing condition.
5. [5]Feeding the Senior Horse- Iowa State University Extension and OutreachgovThat aged horses lose body condition and muscle along the topline because they process certain nutrients, most notably protein, less efficiently, which is why topline loss alone does not confirm PPID.