Oppinions on an odd lameness- vet thinking EPSM but I want more ideas?
I have been dealing with some very strange lameness issues for the last 2 months and my vet and I are stumped. Started off looking lame in front, then moved to back (stifle and hip area), then it looked like there was something in the neck like a pinched nerve. Wasn't consistently off, just would take an odd step here and there. Most recently (Saturday), my horse tied up for no apparent reason. It was cold (about 28 degrees), I was on her for about 10 minutes total... worked in an unheated indoor, first 5 was just walk with a quarter sheet, then started to trot, she felt stiff. After about 2 minutes of trot, I asked for canter and I got what felt like a dead lame horse. I jumped off, and saw her left hind muscle twitching at the stifle and noticed she was dripping with sweat between her legs. I walked her back into the heated barn, so I could observe her vitals. Temp was at 100, breathing was double the normal rate (and we hadn't gotten through our normal warm up yet), gums were perfectly pink. I called emergency vet and asked her to come out; gave the mare banamine paste as the vet suspected colic even though I told her I thought it was a tie up. Mare refused to move her hind legs and was pawing with front legs. Once the vet arrived (about 30 minutes later), she confirmed it wasn't colic and did look like tie up, but was puzzled as the muscles were not hard, but mare couldn't move her hind end without becoming very unbalanced (looked like she was going to fall over). Her breathing was back to normal, as was her heart rate. Vet thinks it could be EPSM that is causing the odd lameness and most recent tie up. She didn't take blood to check muscle enzymes because of the holiday weekend and labs being closed, said the sample would degrade too much by Wednesday. She wants to give her a week off and see what happens (she has been on banamine (4 days), ace (3 doses since Saturday), and muscle relaxers (2x per day for 4 days, then once a day starting yesterday). I know I could do a muscle biopsy, but I don't really want to cut into her neck. She is already on a low sugar/low starch feed (Tribute, Kalm N EZ), so to me, this should have prevented anything related to EPSM, but maybe I am wrong? Vet said she really doesn't think it is neurological (EPM), but she said it isn't clearly EPSM either. Anyone have any ideas for me?