False negative PPID?

[Jackie R]

I have a 19 yo mini gelding, Cooper. Last year he had a bout of laminitis. We got him through it with dietary changes, boots, and bute/Equioxx. He tested positive IR, but negative for PPID. The test was run through the lab at Cornell. My vet has done several tests for me before on a aged gelding with PPID so I trust her collection protocols.
Long story short... even though we controlled the IR with a really restrictive diet, the laminitis returned. A second test for PPID was also negative... but the laminitis kept coming and going. Nothing we tried worked. Metformin produced no changes at all in any of his readings. We decided to just try him on Prascend.
The improvement was almost immediate. He began walking more comfortably within days. Now he’s been on it for 6 months and every so often he has a day or two of walking gingerly, but otherwise is sound as a yard ornament. Has anyone had experience with false negatives? I worry that the improvement may be related to seasonal changes and I’m dosing him with Prascend and what would that do to a horse that is truly not PPID.
I may be overthinking it, and I’ll have him tested again this year. But I’m looking for someone with a similar outcome on testing just for the peace of mind. Thanks.

 

[chandab]

I honestly don't know, but perhaps he is pre-cushing's so is more sensitive in the fall with during the fall rise, so would benefit from the pergolide at that time; but could go without or a lower dose during the rest of the year. That's how my Cushing's gelding started; just needed some pergolide in the fall, but none the rest of the year; eventually needing all year with a higher dose in the fall and a lower dose in the spring summer. [I had to up his dose in like August, and I could decrease a bit after the first of the year. I mostly followed his symptoms and appetite to make his adjustments.]

 

[Cayuse]

I have heard of this happening in early stages of Cushing's. One of my vets says re: Cushing's is "treat the symptoms and not the labwork."

 

[chandab]

I have heard of this happening in early stages of Cushing's. One of my vets says re: Cushing's is "treat the symptoms and not the labwork."

Lab work matters, too; but sometimes they don't follow the "book", so you need to do what works for the individual.