Equine Cushing’s: Case by Case

Learn how veterinarians diagnosed and managed six real-life equine Cushing’s cases that strayed from the classic scenarios.
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Cushing
Andy had only subtle and vague signs of Cushing's, including lethargy, white spots, and mild laminitis. Here he is after treatment. | Photo: Courtesy Dr. Sabine Ware

Learn how veterinarians diagnosed and managed six real-life equine Cushing’s cases.

We all know what a horse with equine Cushing’s looks like, right? He’s an old retired guy with a long, curly coat and sore feet. He’s kind of fat in some places, skinny in others.

This type of “textbook” case, however, is far from standard. Also known as pituitary pars intermedia dysfunction (PPID) or hyperadrenocorticism, equine Cushing’s disease leads to an overproduction of hormones such as adrenocorticotropic hormone (ACTH) and cortisol. Classic signs include, yes, an abnormal hair coat and a failure to shed, but also abnormal sweating, loss of muscle mass, and increased water intake and urination, among others.

If and when Cushing’s horses get to the point of looking like the stereotypical case, it’s often in a very late stage of the disease, veterinarians say. And as with many illnesses, the longer we wait, the harder it is to fix.

The good news is the opposite is also true, says Sabine Ware, BVSc, CERP, equine veterinarian at The Vet Practice, in Victoria, Australia. When diagnosed early and treated promptly and properly, PPID horses have the best chance of leading normal lives.

Melissa Restifo, DVM, Dipl. ACVIM, internal medicine specialist at Brandon Equine Medical Center, in Florida, agrees. “Diligent owners are paramount for that,” she says. “They pick up on subtle signs, meaning we can treat the disease before it becomes a real problem.”

In this article Ware and Restifo share real-life stories of Cushing’s horses they’ve treated that stray from the classic scenarios.

Andy: The lethargic one with changes in body shape

12-year-old Australian riding pony cross gelding

Andy was a “very loved pet” who had been used for leisure riding and harness driving. A plump sorrel pony gelding with a body condition score (BCS) of 5 out of 9, he stood about 14 hands.

“He was the calm soul of the farm, with a kind eye and relaxed personality among a farm full of high-spirited dressage horses,” Ware says.

Andy’s owner first noted that her pony was developing strange white spots, about 2 inches in diameter, across his body. “His coat was quite short and shiny, and overall he looked like a healthy pony,” Ware says. “He didn’t have that long curly coat that most people consider to be classic.”

Over the next few months he became increasingly lethargic and finally “ended up with a big, pendulous abdomen,” she says. About the same time he came down with subtle signs of laminitis, a common side effect of PPID if affected horses’ insulin levels are high. “He didn’t get excruciating pain—just increased pulses (in the feet) and very slight (hoof) changes,” she says. “In general, all his signs were mild and vague.”

Indeed, this confusing case didn’t shout “Cushing’s” in the beginning, says Ware. At first she suspected a viral or an immunosuppressive disease and tested accordingly. She also tested his thyroid function and for insulin resistance (IR, a decrease in tissue sensitivity to insulin that often accompanies PPID). And, just to be sure, she ran an ACTH test for equine Cushing’s. The tests showed Andy had both PPID and IR.

Ware started Andy on a daily low dose of the FDA-approved PPID drug, pergolide, which comes in tablet form and is designed to lower ACTH production. She and Andy’s owner also put him on a restricted diet to control his IR.

Within a year the pony transformed completely despite a few initial laminitic flareups. “All his spots went away, his abdomen tucked back up, his laminitis got under control, and he went back to being his brighter self,” Ware says.

Andy benefited from his medication over the next four years, feeling great. He was euthanized due to an unrelated injury at age 16. 

Bobby: The one losing lots of weight

26-year-old Thoroughbred gelding

Bobby was living in partial retirement. He’d been used for trail riding and leisure, but his owners hadn’t had time to ride him in a couple of years. His owner hoped to get the gray 15.2-hand gelding started on the trails again.

The aging horse wasn’t lacking in attitude, says Ware. “He was bright and pushy,” she says. “He’d definitely drag you out to the grass if he wanted some.”

But Bobby had experienced dramatic weight loss over a short period. “He seemed bright, healthy, and strong, but was just struggling in terms of weight,” Ware says.

Bobby’s owner was worried that his melanomas (a type of skin cancer) were causing his weight loss, so she scheduled a veterinary checkup.

Ware noticed very mild dermatitis (itchy skin inflammation) on Bobby’s back pasterns, but no rings on his hooves or other signs of laminitis. His coat was fine, and he had good teeth for his age.

She performed a blood workup and found nothing remarkable there, either. “There were no red flags,” she says. “Liver, kidneys … everything was within normal limits.”

On a hunch—and given his age—Ware screened him for PPID that summer. The result? An ACTH value of 110 picograms/mL. “That’s a very high finding,” she says, noting that ACTH fluctuates naturally from season to season. “This time of year you’d want a reading of about 47 max.”

At press time Bobby had only just been diagnosed and started on the initial dose of 1 mg/day of pergolide.

“We’ll retest him in four to six weeks to see where his levels are, and we’ll increase it as we see fit,” Ware says. “It’ll be interesting to see how quickly he evolves.”

Rosie: The one with eye and skin problems

22-year-old Thoroughbred Mare

Despite her age, 15-hand Rosie was still competing in three-day eventing. Even when her subtle signs of PPID began to develop, she continued her regular athletic activity. Rosie’s owner fed her a sport horse diet of high-quality forage and concentrate feed, and the mare was maintaining a BCS of 4.

Rosie’s owner first noticed the mare’s eyes weeping for several weeks. Around that time, Rosie’s black coat started growing in half gray in “weird patches,” ranging in size from a few inches to covering entire body parts. She grew calmer and breathed more heavily than usual during exercise. Eventually she developed “horrible mud fever” (e.g., scratches) with dermatitis lesions on her legs. Her eyes would crust over, and as the disease advanced, she acted increasingly lethargic.

Rosie’s coat never grew long, and she never developed full-blown laminitis—­although Ware recognized abnormal growth rings on her feet. “So she was having minor bouts of laminitis apparently, but they were so mild they just weren’t getting picked up,” Ware says.

She first tried flushing Rosie’s tear ducts. “But we didn’t get the results we wanted,” she says. That, combined with the coat and skin issues and the mare’s age, prompted Ware to suspect PPID. “I was also flagged by the mare’s poor muscle tone,” she adds. “For a horse in that level of work and with that quality of feed, she didn’t have the right body type.”

When testing revealed the mare had PPID, Ware started Rosie on the standard dose of 1 mg/day of pergolide and tested her ACTH levels four weeks later. Because they were still higher than normal, Ware increased the dose to 2 mg/day. “And that’s where we saw the most dramatic results,” she says.

Rosie’s gray patches disappeared, and her eyes and skin cleared up. She also gained back her energy and personality. “It was great to see her bright attitude when I came for checkups,” Ware says.

Several months later, Rosie is back to being a fit, muscled all-black eventing horse. She’s still competing, still on the same diet, and looks and feels great. “The only change was the pergolide, and that made all the difference,” Ware says.

Rosie before
Rosie's owner first noticed the mare's eyes weeping for several weeks. Around that time, Rosie's black coat started growing in half gray in 'weird patches,' ranging in size from a few inches to covering entire body parts. | Photo: Courtesy Dr. Sabine Ware
Rosie after
After just three months of aggressive pergolide treatment, Rosie's muscle tone and hair coat returned to normal, and she regained her energy and personality. | Photo: Courtesy Dr. Sabine Ware

Luke: The one with topline loss and frequent urination

22-year-old Morgan gelding

Luke is a cherished bay pleasure horse enjoying a comfortable retirement. His owner had ridden him on trails and trained him in natural horsemanship with lots of groundwork.

“He’s a real ham,” Restifo says. “Very laid-back, easygoing, goofy, inquisitive, and always getting into stuff.”

Luke’s very observant owner first realized her horse was losing muscle across his topline, Restifo says. Then she noticed he was developing an unusually long coat and was urinating frequently.

Restifo came to see Luke for an annual wellness check. When his owner mentioned the signs she’d seen, Restifo ran tests and determined he had PPID. She started him on 1 mg/day of pergolide, and his owner made changes to his environment, such as reducing turnout time on grass to limit sugar intake that could exacerbate his insulin issues.

“It took about two to three months to see a response in his coat and weight,” Restifo says.

Three years later, Luke is now on 1.5 mg/day of pergolide. He continues to drink and urinate normally, and his coat is healthy. Because he received treatment so early in the disease process, Luke hardly suffered from its consequences.

“This owner’s diligence has really made all the difference for Luke,” Restifo says.

D.J.: The poster child for obscure PPID

16-year-old Thoroughbred/Warmblood-cross gelding

D.J. had been a successful hunter before becoming a pleasure horse. He lives with his owner in the northeastern U.S. and has always been in good health.

Restifo says D.J. suffered from recurrent corneal ulcers in both eyes, as well as urinary tract infections (UTIs). His ulcers took a long time to heal, and his UTIs were resistant to multiple ­antibiotics.

While he never had any issues with his feet, his treating veterinarian suspected he might have equine Cushing’s early on, due to his coarse, poorly shedding coat and difficulty maintaining weight and topline. The initial bloodwork, however, came back normal.

The gelding has been a “real poster child for obscure Cushing’s cases,” Restifo says. She suspected she was getting false negative results from a basic ACTH test. So she sent his blood for a more advanced thyrotropin-releasing hormone stimulation test, which revealed ACTH levels of well over 200 for a reference value of 110. “So that was a pretty clear positive,” she says.

She started him on 1 mg/day of pergolide, while simultaneously treating his UTIs and ulcers. Every six months she retested his ACTH levels—but they were never under control, despite increased pergolide doses. “After several rounds of increasing his dose, we started testing him every four to six weeks,” she says. “We finally got his levels down to normal, but it took getting him up to 2.5 mg/day.”

Restifo continues to test D.J. every six months. Now at age 17, he’s up to 3.5 mg/day plus a dose of ­cyproheptadine—­veterinarians’ treatment of choice pre-pergolide. “We still use it occasionally in horses that have really refractory (unmanageable) disease,” Restifo says. Cyproheptadine isn’t as powerful a drug as pergolide, but horses can’t have unlimited pergolide, so she says cases like D.J.’s require a mix.

At his current dose D.J. stays healthy and UTI- and ulcer-free.

Hairy: The Advanced Case

25-year-old Miniature Mare

This tiny blue-tan gruella Mini had been rescued from a kill pen. Named for her massive hair coat, Hairy was “the sweetest little critter I ever met,” Restifo says.

The mare was in extremely poor health at the time of her rescue, with a heavy coat and very long feet riddled with clear signs of chronic laminitis.

Hairy’s new owner cleaned her up and had her teeth taken care of and bloodwork done. Her ACTH levels were at 400. “She had pretty substantial disease,” Restifo says.

It took three to four months to get Hairy’s PPID under control with pergolide. This was, in part, because “she would get a natural rise in hormones in preparation for the winter, putting her ACTH out of whack,” Restifo says.

Meanwhile, her owner managed her laminitis signs with two years of specialized farriery and other medical procedures, such as a neurectomy (cutting the pain-signal nerves to the feet), to “make her comfortable,” she says. She also administered low levels of non-­steroidal anti-inflammatory drugs (NSAIDs) as needed to help keep the pain at bay.

Hairy’s condition was already very advanced when PPID treatment began, Restifo says. Despite the medications, she wasn’t getting enough relief. Worse, the NSAIDs—long-term administration of which is known to cause gastric ulcers—upset her stomach. “Her owner felt like she had tried everything to make the mare comfortable,” she says. “But in the end, she did feel like the most humane choice was to euthanize her.”

Although Hairy didn’t survive her multiple health disorders, she benefited from treatment. “She got the best care and the most attention and affection at the end of her life,” Restifo says. “It was as good as it could have been.”

Take-Home Message

Equine Cushing’s disease comes in all forms and fashions. But PPID horses that benefit from close relationships with attentive owners who treat them properly stand the best chance of living well, our sources say. By recognizing that horses are not their usual selves, owners often pick up on the subtlest signs of PPID before their veterinarians might. “Cushing’s isn’t always textbook, and these horses are proof of that,” Restifo says.

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Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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