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Examples of PSSM symptoms include

- overall stiffness
- the horse appears lazy or cannot move out
- intermittent and/or shifting lameness
- tense belly
- the horse resents being groomed, saddled or cinched up
- the horse seems difficult to train and may display unwanted behaviors such as bucking, rearing or balking
- muscle spasms that can occur all over the horse’s body but are most often seen on the flanks, neck and shoulders
- the horse is unable to move and stretches out as if having to urinate
- general signs of pain (flehmen, "pain face", distancing themselves from the herd)
- excessive sweating
- hard muscles, especially of the hind quarters
- pawing the ground
- frequently rubbing the body and especially the hindquarters on solid objects or leaning on them with the hindquarters
- difficulty standing for the farrier
- difficulty standing in cross ties
- difficulty or resenting being trailered 
- a sudden decline in musculature
- excessively low and long head carriage on the lunge line, esp at a trot
- standing with their legs under them (like a goat on a rock) or parked out
- nervous behavior with a tendency to excessive spooking
- gait abnormalities (esp. type 2)
- coffee colored urine during serious episodes (esp. type 1 and Px)
- recumbency during particularly heavy episodes (esp. type 2)

 

What seems to be fairly typical for a horse with PSSM is that they tend to have difficulty bending through their body, achieving collection under saddle, backing up, lunging and loping when they are symptomatic. The latter (“when they are symptomatic”) is an important aspect to keep in mind, because many PSSM horses go through phases of being more or less or non-symptomatic, which makes them appear unaffected during non-symptomatic periods.  

The expression of PSSM symptoms can be quite varied, even within one and the same horse. Many of these symptoms are general pain symptoms, which often makes it difficult to come to a diagnosis. Often, horses that end up being diagnosed with PSSM have been diagnosed at one point or another with for example colic, tying up, laminitis/founder, knee injuries or behavioral or training issues. In more severe cases, neurological problems are suspected, because the horse seems to be losing control over its own body. Lyme and EPM can also present with very similar symptoms to PSSM. Genetic testing offers a diagnostic tool to determine whether or not PSSM might be the root cause of a horse’s symptoms.

Possible PSSM type 2 symptoms are quite similar to those associated with PSSM type 1. What seems to be fairly distinctive is that PSSM type 1 (and Px) affected horses usually present with (often severely) elevated CK, LDH and/or AST levels, especially after exercise. In PSSM type 2 horses, these values are usually barely elevated at all.  PSSM type 2 horses on the other hand, can cause very distinctly visible muscle damage, gait abnormalities and intermittend unexplained lameness. In some horses that have PSSM type 2, the muscle damage can show up as "divots", especially in the shoulder area and on the hind end. These divots sometimes disappear when the horse is managed, or may change shape and present as ripples under the skin. Horses with PSSM type 2 often have an increased muscle tone. Another finding in horses with PSSM type 2 is that they never seem to move straight; the rider always has the feeling that they are crooked, which the rider can't correct. Gait abnormalities can present as rope walking (feet are placed in front of one another instead of beside one another as if the horse was walking on a tight rope), bunny hopping (both hind feet are moving forward simultaneously at the galop, which makes it look like a rabbit hop rather than a galop), cross-firing, stringhalt (esp. in warmbloods) or an uncoordinated way of moving (can look similar to neurological problems). 

 

Most horses with PSSM type 1 become symptomatic when they start their training. In heavy horses, symptoms may present differently then in lighter horses. Most horses with PSSM type 2 become symptomatic when they are between 7 and 10 years of age, even though owners often report the horse "not being quite right" or having had strange locomotive issues even as a young horse. 

 

It needs to be stipulated that practically no PSSM affected horse will show the same symptoms and that they can also present with symptoms that are not mentioned in this article. Often, PSSM affected horses are individuals that have gone through many rounds of tests and vet checks, without the vet having found a suitable diagnosis that covers all of the horse’s problems.