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The early symptoms of PSSM2 are quite mild: stiffness during gait changes, lack of power from the hindquarters, high muscle tension, difficulty building muscle, and pain-related behaviour changes. PSSM2 is a progressive disease and affected horses develop more severe symptoms with time. Many horses develop shifting, unclear lameness. Some horses show muscle atrophy at the hindquarters, shoulders, and/or topline, which may be in addition to areas of focal muscle atrophy which can look like “kick marks”. The severe tying-up episodes found in PSSM1 horses are rare in those with PSSM2.


Acute episodes of muscle atrophy often appear when affected horses experience negative nitrogen balance, when the body needs more protein than they get from their diet. This often happens when a horse is very stressed, for example during an illness, infection, or after and operation.  A horse with optimized nutrition with a high protein content that never experiences negative nitrogen balance may only ever experience mild symptoms.


The first obvious symptoms often are noticeable when horses are 7-10 years old, but may appear earlier or later depending on environmental influences (diet, exercise, etc.).


Order the Muscle-Integrity-Myopathy 6-Variants-Panel (PSSM2) 

Typical symptoms equine myopathy "P2, P3, P4, P8 and K1" (Myofibrillar myopathy - MFM)

  • Pain-related behavioural changes

  • Shifting lameness

  • Stiff hindquarters

  • Difficulty building muscles (especially hindquarters)

  • Difficulties with gait changes

  • General muscle loss (especially hindquarters and shoulders)

  • Focal muscle loss (appearing like kick marks)

  • Coordination problems or atactic gait

  • Muscle tremors, tension or cramping

  • Even with obvious symptoms of muscle disease, the blood levels of Creatinine Kinase (CK) and Aspartate Aminotransferase (AST) are usually within normal parameters