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EAY
Nov. 27, 2009, 06:21 PM
The vet is coming out in a few days to give my son's 18-year-old Welsh cross pony an ACTH test for Cushing's and I want to be in the position to make educated decisions after the results are in.

The reason for the tests is that when the vet came out in early June to do the pony's teeth she felt that he had not sufficiently shedded out. Though I did agree with her, we had had a cool spring and it seemed like lots of the horses were not shedding out as usual. We bought the pony last winter so I am not sure what is typical for him. Also, he had lost quite a bit of weight and was generally in fairly poor condition so I wondered at the time whether that was a factor.

He did eventually shed out, though I must say he was quick to get his winter coat back this fall. Also he does have some fat deposits above his eyes, but other than that I don't see other clinical signs - no excessive water drinking and/or urination, cresty neck or other unusual fatty deposits. He gained the weight back nicely over the summer, has good energy levels, and has not been sick since we got him. In fact, he seems (knock on wood) resistant to a rain rot epidemic that they've been having at the barn where we board, so I took that to be a good sign about the state of his immune system.

He did have one previous mild (according to his previous owner who had him for years) pasture associated laminitis episode and was foot sore on one foot about a month ago. The farrier said he couldn't rule out laminitis but thought it was more likely the result of a bruise. There was no indication of an abscess.

I am concerned because I know the tests can have false positives, as well as negatives, and that clinical symptoms are necessary to give a diagnosis. The vet feels that the failure to shed out normally would be sufficient in conjunction with a positive test result to give a diagnosis of Cushing's and to recommend that the pony start drug treatment.

Does anyone have experience with false positive results? Is it not unusual for a Cushingoid pony to have so few symptoms? I know I'm kind of jumping the gun here and of course am hoping for a negative result, but at the same time I want to be ready and in a position to do what's best for the pony.

rcloisonne
Nov. 27, 2009, 06:55 PM
Does anyone have experience with false positive results? Is it not unusual for a Cushingoid pony to have so few symptoms? I know I'm kind of jumping the gun here and of course am hoping for a negative result, but at the same time I want to be ready and in a position to do what's best for the pony.
Sometimes delayed shedding is the only symptom early in the disease. Your pony has also had a couple of mild bouts with laminitis. This could be due to insulin resistance so it would be a very good idea to have his insulin level checked.

If I were you, I would delay testing for Cushing's until late Dec or early January. There was a study done that showed a number of false postives due to time of the year (Aug- Dec). Too bad your vet didn't test him in June.

llsc
Nov. 27, 2009, 06:59 PM
Yep. Not a good time to test. Wait until spring to get an accurate result.

EAY
Nov. 27, 2009, 07:20 PM
Your pony has also had a couple of mild bouts with laminitis. This could be due to insulin resistance so it would be a very good idea to have his insulin level checked.

He's only had one bout of laminitis, as far as I know, and that was because he was accidently put out a very lush spring grass without a muzzle.

She also will be testing his insulin level as well as cortisol.

If I were you, I would delay testing for Cushing's until late Dec or early January. There was a study done that showed a number of false postives due to time of the year (Aug- Dec). Too bad your vet didn't test him in June.

She said this was a good time for the test.

rcloisonne
Nov. 27, 2009, 07:39 PM
She also will be testing his insulin level as well as cortisol.
ACTH tests for, well, ACTH (adrenocorticotropic hormone), not cortisol.


She said this was a good time for the test.
She's wrong. No need to wait for spring, however. Dr. Mark Donaldson's work at New Bolton showed normal horses with elevated ACTH levels in September were normal by late December.

http://www.ecirhorse.com/index.php?option=com_content&view=article&id=28&Itemid=38

Send a copy of this to your vet:

http://cal.vet.upenn.edu/projects/equinebehavior/publixs/Papers/Donaldson_et_al_2005.pdf

Hopefully, she is familiar with the special handling and precautions required to get an accurate ACTH measurement. If not, ask her to go to the Cornell veterinary lab testing site. If not done properly, you'll be wasting your money.

sdlbredfan
Nov. 27, 2009, 07:40 PM
The so-called seasonal rise in ACTH affects all horses, but some research I've read indicates that in those equids with PPID aka Cushing's, the amount of the rise is higher than the average non-cushinoid critter. Thus, it is not wrong or a waste of time to test at this time of year. If it is abnormally high, that indicates Pergolide would be needed, and after seasonal rise wraps up, another ACTH can show if level has come down to normal or remains elevated. If it remains elevated, that would indicate pony probably needs to continue on meds. There is a lot of good info on www.ecirhorse.com

Kudos to OP's Veterinarian for being up to date in knowing that ACTH is the test to use, not Dex Suppression! Yay! (The DST can push a borderline laminitis prone critter into full blown laminitis, and with pony having had that already, that is great the Veterinarian knows to avoid it.)

EAY
Nov. 27, 2009, 08:14 PM
ACTH tests for, well, ACTH (adrenocorticotropic hormone), not cortisol.


I meant to say that she is testing for ACTH, insulin, and cortisol.

Fairview Horse Center
Nov. 28, 2009, 09:04 AM
We often have horses not finished shedding by early June, and ponies often start puffing a bit the last of August. I am not one to jump on the Cushings bandwagon, no matter what any tests say. IMO, it is an "in vogue" diagnosis. When I saw a "true" cushings horse, the coat was not just long, but extra long & thick, easy to be very matted, and never shed at all.