What looks like HYPP but isn't?

[Scribbler]

I posted a while back that my overo Paint mare (chestnut, lady body builder type) had what looked to me like a classic HYPP episode of major muscle twitching about a month after I started her on a new Vitamin Mineral Supplement that contained potassium. I stopped the supplement and had her tested.

Well, the gene blood test went to UC Davis and came back negative. So what else would cause an isolated episode like that?

I’ve been browsing HYPP info in the meantime and it seems significant that she doesn’t have quite as much stamina as you’d expect given her build, that she loves salt and can consume a pound a week in summer, that she has never loved being brushed and that she has the most gorgeous muscles.

She’s otherwise in fantastic health, no neuro symptoms and we aren’t in a region with insect borne diseases. Easy keeper.

[Ponycatraz]

Did you test for PSSM as well or just HYPP?

[B_and_B]

Second the suggestion to look into PSSM, both PSSM1 and PSSM2. One, I believe is tested for by genetic markers; while Two is the absence of the genetic marker but a positive on the muscle biopsy. If I remember correctly! Quarter Horses have been shown to have both One and Two, but One is more common in the breed, I’d guess that Paints are going to be similar.
In both instances horses can have the ‘body builder’ body, it is only in the extreme cases of uncontrolled PSSM that you have muscle loss. Thankfully, we’ve come a long, long way in understanding how it all works.

[WildGooseChase]

Another vote for PSSM 1 and 2 tests. Both types are very prevalent in stock type horses (type 1 has shown in 20 different breeds) . They only need one copy to be symptomatic. There were rumors that breeders are/were breeding halter horses intentionally with one copy of PSSM for better muscle tone in the show pen.

[Scribbler]

I’ve looked at the symptoms for PSSM and HYPP. The wierd muscle twitch episode was classic HYPP and she has no symptoms of PSSM. I didn’t get the PSSM test because my vets office told me they didn’t bundle the tests. But also I haven’t seen any PSSM symptoms. No tying up, no topline problems.

My research says it was HYPP that was being perpetuated in some halter lines because it could make bulkier muscles. PSSM can have a negative effect on topline. It’s also way more common across different breeds.

I

[WildGooseChase]

Muscle tremors are a symptom of PSSM, which you said happened to your mare. Laziness and lack of willingness to move forward is as well. If nothing else, a test would rule PSSM 1 and 2 out. With how prevalent it is in stock horses, and the episode she had, it’s worth the money and peace of mind. You can send in a $40 PSSM1 test yourself through UC Davis. It’s hair follicle test.

[WildGooseChase]

Also, many horses with PSSM are overweight at the time of diagnosis. I wouldn’t go off her topline being normal.Here’s a chart from Michigan State Univerisity’s write up on PSSM 1&2.

[Scribbler]

She isn’t currently overweight.

What symptoms of PSSM would line up with what I’ve observed in her?

[WildGooseChase]

The muscle tremors and lack of stamina. I would 100% have this horse tested for the peace of mind. It’s better to have it done and come back negative to rule it out than the alternative of not testing and her being positive with no diagnosis. PSSM episodes can be mild, induced by exercise or idiopathic (meaning no trigger, it just happens). It can got unnoticed for years if the horse is on good turn out and an appropriate diet.

[JB]

@Scribbler

Well, the gene blood test went to UC Davis and came back negative.

do you mean hair test?

Ditto the PSSM comments. Hair test for Type 1, muscle biopsy for a MUCH more definitive result than any hair test with EquiSeq

Type 2 (which really shouldn’t be called PSSM of any sort, it’s not a glycogen storage issue) has many components, including MFM (Myofibrillar Myopathy) and RER (Recurrent Exertional Rhabdomyolysis aka classic tying up)
What Is PSSM2? - PSSM & MFM AWARENESS (pssmawareness.com)

[Scribbler]

The vet pulled blood for the HYPP test.

[JB]

I was unaware of any blood test for HYPP. Are you sure that was the actual test? Or was the bloodwork to analyze muscle enzymes to determine a tying up episode?

The UCD site doesn’t mention any blood testing, just hair. But maybe that’s just for the general public
Hyperkalemic Periodic Paralysis (HYPP) | Veterinary Genetics Laboratory (ucdavis.edu)

[Scribbler]

Wouldn’t the blood have genetic material?

[JB]

white blood cells do have DNA. I’m just not aware that anyone is doing that testing for HYPP, but maybe that’s a vet-only option. If your results say n/n for HYPP then I guess that’s what they are doing. I would imagine the hair analysis sent in yourself would have been cheaper.

[mmeqcenter]

I too have not heard of a blood test for HYPP, and I’d double check that HYPP was actually tested for. Then I agree with the rest and test for PSSM.

[Scribbler]

The vets service forwarded me the results from the place that sent it to UC Davis. I’m in Canada, I suppose I could also send hair off but I did also want my good vet in the loop.

[jvanrens]

If she’s registered APHA, you could do testing through them with UC Davis and her file would be updated with them. Normally just a hair sample (mane or tail hairs with the root attached) is sent through the mail directly. The information should all be on their website. You likely could have done the complete six panel test through them for the cost of the blood draw and shipping.

Maybe you can find a tactful way to let your vet know there is an easier way to do the testing.

[vxf111]

The PSSM Type 1 test is super cheap and non invasive. For sure I would pull mane and send that in for testing. It’s only around $40ish.

Your description matches how some stock type horses present with PSSM.

[Equkelly]

My mare is suspected to be pssm2 but she’s too young for a muscle biopsy so it has not been confirmed. She does have the muscle tremors and twitching but the lack of stamina is probably her biggest symptom. She has had tying up episodes but they don’t really look like traditional full blown tying up episodes like you’d see on the racetrack. Hers are subtle and barely noticeable. From what I understand though most pssm2 horses don’t tie up at all, and the tying up is more common in pssm1.

I recently did the pssm1 test from UC davis and it was super easy and I had the results back in around 2 weeks.

[vxf111]

I used this company…

https://www.animalgenetics.us/equine/genetic_disease/PSSM.asp

It took about 2 weeks including mailing time, which was s-l-o-w. It was about a week turnaround once the samples actually got there.

I also had a couple other tests run at the same time. It was only $40. Cheap, simple, quick(ish), and well worth it for a good answer on PSSM 1 (my horse was negative).