The EPSM/PSSM group is for anyone who owns a horse with EPSM/PSSM or suspects their horse may have this condition.


Polysaccharide Storage Myopathy (PSSM), also referred to as Equine Polysaccharide Storage Myopathy (EPSM), is a common form of tying-up in many horse breeds and is characterized by excessive and abnormal storage of sugar (polysaccharide) in muscle cells.


Horses showing these signs:


  • Muscle stiffness, cramping or pain 
  • Muscle fasciculation (twitching, quivering or spasm) 
  • Exercise intolerance
  • Firm (hard) muscles, especially in the hindquarters 
  • Lameness, stiff choppy gaits, tripping 
  • Discolored, dark or brown urine (myoglobinuria)
  • Progressive weakness
  • Difficulty backing up, reluctant to pick up hind legs


may have EPSM/PSSM, which can be confirmed by diagnostic testing through the Michigan State University (muscle biopsy and clinical information) and University of Minnesota (genetic testing). See files for details. 


As more is learned about these neuromuscular conditions, new approaches for managing EPSM/PSSM and other neuromuscular disorders through genetic research, nutrition and training are emerging. This group will combine information on resources, research and the experience of other group members to help you find the best approach for your situation and regain your equine partner.


New members will have their initial posts moderated to prevent spam and inappropriate material. Advertising, solicitation by private email and selling products or services are not permitted. Please contact the group moderators if you have any question about these policies.

We are working to preserve important archived information from the legacy EPSM/PSSM group. Moderators are reviewing information from the original files and will repost pertinent files as well as identifying and posting more recent knowledge. 

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