01/09/2024
Howdy and happy winter to all my fellow, crazed, horse fanatics (Or happy summer to those fortunate enough to live in the southern hemisphere...ya'll are true "southerners")
It's interesting to consider, that, while I'm getting older, my patients appear to live longer, as well. This is due to a combination of nutrition, medical care, maybe genetics and no small amount of luck. As I see more older patients, I see more of 'em with diseases specific to geriatric patients. Here's a summary of one of these:
“He has…What ?”, the owner was a bit confused, befuddled, even, which is not surprising, as Pituitary Pars Intermedia Dysfunction (PPID), AKA “Cushing’s Disease” doesn’t just roll off your tongue. “I didn’t know a horse had something called a Cushings. What and where the heck is it”, he added.
Well, this disease is named after the neurosurgeon Dr. Harvey Cushing, who first discovered these benign tumors in the pituitary gland and related them to a variety of symptoms in human patients over a century ago. This also affects other mammals and is a common problem in older horses. It is technically cancer, but not the kind that will spread to other organs and kill you quickly. No, instead it just makes you sick and kills you slowly…no real consolation prize.
In horses, the big giveaway is found in their inability to shed (see photo below). So, if your old horse looks like a woolly mammoth, but shorter, with four inches of hair in July, that’s what ya got. And other things like laminitis leading to founder, heart problems and a long list of diseases you don’t want to see in your horse, add to the problems. There are blood tests to confirm our suspicions, but the results can vary with season, so they can be a challenge to interpret. So, if it looks like a duck…etc.
The pathology of this type of brain cancer is interesting and complicated, but it is basically due to a deficiency in dopamine. This hormone, a class of “neurotransmitters”, is responsible for a lot of things. One of its main functions is to stimulate the pituitary( see photo for the approximate location of this gland in the horse...right in the middle of their head, at the base of the brain), a vital gland located at the base of the brain (see illustration), to secrete other hormones… several of ‘em. Dopamine is interesting by itself. If you have too much, you become schizophrenic, if you don’t have enough, you get the shakes commonly seen in Parkinson’s disease. (I don’t know why some folks insist on naming a disease after themselves…. this makes me wonder if the guy caused it, or just had a case of it, neither is an admirable position, but who am I to judge.) And, some more good news, there is a treatment: Pergolide.
Although it may seem a little strange, lots of modern drugs come from natural sources. Penicillin comes from bread mold, aspirin is from willow bark, ivermectin is from a common fungus in the soil. Pergolide is made from one of many ergot alkaloids that also come from a soil-borne fungus. How they get developed into medical use that is safe and effective is a whole ‘nuther long, long story.
The crazy part of ergot alkaloids is they can cause two basic symptoms: severe, potentially fatal infections that look like gangrene, or hallucinations. Over five hundred years ago, they called the infection “St. Anthony’s fire”. It came from eating moldy grain and it killed thousands of people. But another specific type of ergot alkaloid causes hallucinations—this is where they get L*D! So… eat spoiled corn and either fly to Jupiter on George Washington’s horse mentally, or DIE…really.
As strange as it may seem, another alkaloid from this fungus was used as a headache remedy as early as 1920. How someone decided to take a chance on a potentially fatal, at the worst, or hallucinogenic, at best, fungus as a good drug is…interesting. We could only assume this came from a vivid, albeit fearless, imagination. But apparently, one of these alkaloids has an amazing hormonal pharmacologic property. (How many test subjects had to hallucinate and then die? Well, I guess we’ll never know)
Although this seems like taking the long way home, we learned all that to discover this: one of these ergot alkaloids (Pergolide) acts like dopamine. It has been used to treat human Parkinson’s patients for many years. Well, until about 2007 when they discovered it caused major heart problems—you may have a heart attack, but at least you ain’t shaking during the event! Undaunted by this minor setback, someone in Big Pharma must have realized they needed to do something with the 200 railroad cars full of this stuff. BINGO! He must have thought: “Let’s sell it to horse people!”
It is well known that PPID horses can be “controlled”, not cured, with pergolide. Various reports show an average of 60-80% treatment success. However, these reports can be difficult to interpret as studies classify “success” quite differently. Blood tests demonstrating a reduction in another hormone, ACTH, as a presumed result of pergolide treatment, is typically called “success”. Simple, right, but not so fast, cowboy: this stuff aint just a spoonful of castor oil. The drug ain’t cheap, is by prescription only, and is reported to cause a high number of adverse effects. Some of the most common include anorexia, colic, weight loss, and a change in behavior/attitude. Anorexia has been reported in up to 32% of horses on pergolide in some studies. It gets “better”.
Harold Schott and his colleagues, in a study reported last year, demonstrated that Cushing’s horses treated with pergolide did not live longer than non-treated patients. Both groups lived about three years after the initial diagnosis. However, the quality of life may be significantly better as treatment tends to limit the onset of laminitis and “comorbidities”—other diseases--seen due to the altered metabolism caused by the abnormal amounts of hormones secreted by the tumor.
So, if your horse lives long enough, there’s a good chance you’ll see Cushing’s symptoms. The questions of treatment, costs and quality of life are something we eventually must face when dealing with our horses. It ain’t fair, it just IS. Strive for perfection, accept only excellence, ride with purpose.
If you like my twisted way of thinking, give us a “like” and share here and check out our website: www.cornerstonequine.com for more out of the box thinking and a link to my virtual, online consultation service. And, I almost forgot, the book is available in print, e-book and audio formats, performed by yours truly, on Amazon: Never Trust a Sneaky Pony (and other things they did not teach me in vet school) It makes a great gift, or birdcage liner, your choice.