Re: Very high ACTH, no symotoms


Kirsten Rasmussen
 
Edited

Bonnie,

I don't see why a high ACTH couldn't be present with no signs.  Most people don't test until there are signs of disease so maybe there are lots of horses with no signs but high ACTH out there?  There are multiple hormones involved in PPID and perhaps if the others aren't elevated as well you won't see signs of PPID.  I do still wonder if the lack of signs means there is no... 

..."hypertrophy, hyperplasia, and microadenoma formation within the pars intermedia. These conditions contribute to excessive ACTH production, and the enlarged gland places mechanical pressure on adjacent tissues, inhibiting function of the pars distalis and pars nervosa. The resultant functional changes and the excessive release of ACTH into the body result in clinical disease"
https://www.vetfolio.com/learn/article/equine-essentials-equine-cushings-syndrome-pituitary-pars-intermedia-dysfunction

If there are no signs of clinical disease other than grossly elevated ACTH, then is there still enlargement of the pars intermedia?  Perhaps there is no definitive answer to that question beyond an autopsy.  As Martha indicated in her reply to you previously  https://ecir.groups.io/g/main/message/256192
ACTH isn't the only indication that PPID is well-controlled and other hormones are involved.  Dr Kellon has also said:
https://ecir.groups.io/g/main/message/255735 : There is no direct link between ACTH  and insulin levels.  Studies have shown cortisol is often normal and much of the measured ACTH  may be inactive. However, we use ACTH as an indicator of control over the PPID.  ACTH is actually  only a small fraction of the hormones released by the intermediate lobe, and all of them can have a negative effect on insulin sensitivity.

https://www.ncbi.nlm.nih.gov/pubmed/6141515 
https://www.ncbi.nlm.nih.gov/pubmed/3035302
AND 
https://ecir.groups.io/g/main/message/215025 : Also important to note there are some PPID horses whose hormonal profile doesn't include obviously elevated ACTH.  In fact, this group founder's mare was like that! It probably shouldn't be surprising when you consider that of all the hormones put out by the pituitary in PPID, ACTH is by far at the lowest concentration. We're way past the time to switch to testing POMCs across the board or alpha-MSH instead.
So I dont think there is an obvious answer to your question about whether extremely elevated ACTH but no symptoms means the disease is present.  Maybe Joseph is in the earliest stages and early treatment will reduce the severity of his PPID (signs, such as laminitis, and hypertrophy of the PI gland) as he ages.  Is it possible there are subtle signs you may have missed?  If you notice any changes while he is on pergolide that could be an indication that what you thought was normal for him is not (similar to Martha's experience with skin conditions in her horse Logo).  Or maybe Joseph will never develop the signs of PPID and always have high ACTH, regardless of whether or not he is treated.

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