My horse was diagnosed with Cushings in June based on clinical signs. He had a normal ACTH level at that time. Since, we’ve been dealing with several different issues that are difficult to pin down to the Cushings specifically. My vet wants to run another CBC and Chem panel along with the TRH stim test. I’m guessing the stim test would be to get a more accurate diagnosis of Cushings.
After doing some reading, I’m finding that it’s only recommended to run that test from mid November to mid June. Any thoughts on this?
We are in the ‘seasonal rise’ period of ACTH testing being likely to show elevated levels, even if not clinically significant earlier. If the ‘working diagnosis’ is Cushings, aka PPID, starting on Prascend would be a smart idea, of not already done, IMO. Be sure to read the ECIR group information, if you have not already.
Our farm (retirement farm - Paradigm Farms in TN) was part of the studies to establish the baseline data for the TRH stim test. To my knowledge the test should only be done December through June, as baseline numbers for the post-stim ACTH have not been established outside those months.
That being said, a horse can still have PPID (Cushing’s) with a negative test. Even with the TRH stim test, it has been established through post-mortems that there still is no test sensitive enough to diagnose PPID in the early stages. If a horse is showing strong clinical signs I would take that into heavy consideration.
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This is very true. Most veterinarians I’ve talked to agree that any horse that is symptomatic should automatically be treated as a PPID case. You still want to monitor ACTH levels, as medication can only slow, not stop, the disease progression. We do not at this time have the ability to diagnose PPID until the horse has reached a relatively advanced phase of the disease (based on the results of post-mortem studies, as mentioned above).
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Jack is on Prascend 1 mg/day. So would it do any good to run this test, or just a waste of money? I suspect we have other issues, and wonder if this is just a way for my vet to get me to ‘shut up’.
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If the horse has already had a diagnosis of PPID and is on prascend, I would simply pull ACTH levels going forward. We have done repeated TRH stim tests on several of our PPID positive horses as part of the studies over a three year period. My takeaway from my spreadsheet is that the TRH stim test is better than a baseline ACTH at diagnosing PPID, but the post stim numbers get harder to interpret after that point. Currently at our farm we use the TRH stim to diagnose, and then use simple baseline ACTH for ongoing monitoring. Long winded way of answering your question is that no, I wouldn’t do the TRH stim test at this time. If you need to check levels for monitoring and management purposes go with the baseline ACTH.
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This is well-written, and makes sense to me.
