Re: Adjusting pergolide when base numbers are normal

Kirsten Rasmussen

I have been advised that TRH stim testing is not generally done after a positive PPID diagnosis so how am I supposed to manage this horse’s pergolide dose?  Do I only pay attention to the pre-test numbers? 

This question has been asked many times and I feel like we just don't have a good answer for it. However,  the 2019 EEG Guidelines on PPID do state in Table 5, under Initial Response, that you should see "decreases in basal ACTH and ACTH 10 min after TRH administration (but not necessarily to below cutoff values)"

This seems reasonable to me...the TRH Stim should show a reduction in both pre-and post-ACTH numbers, although how much reduction does not appear to be quantified.  There will also be a seasonal effect, so less reduction may be seen during the seasonal rise.  It may be best left to the owner and attending vet to decide if the drop is adequate at that time given that basal ACTH is normal in early cases.  Keeping basal ACTH in the lower-middle part of the range year-round might also be advisable since many PPID horses do best when their ACTH is tightly controlled in the middle to lower normal range.  Also, if the signs that prompted the use of a the first TRH Stim test in the horse improve or go away on medication,  that is another indicator that the pergolide dose is effective.

Karen, I personally would be satisfied with your latest bloodwork numbers for now, but the real test will be if his coat regrows normally and if his airway issues recur on his current dose.  Of course the skin irritations could be a sign that a higher dose would be beneficial, as we know from Martha and Logo's experience, but coat abnormalities in colour could be due to minerals not being balanced to his hay.

Kirsten and Shaku (IR) - 2019
Kitimat, BC, Canada
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