Examples of PSSM symptoms include

- overall stiffness
- the horse appears lazy or can’t 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
- excessive sweating
- hard muscles, especially of the hind quarters
- pawing the ground
- feeling the need to roll immediately after exercise
- frequently rubbing the body and especially the hindquarters on solid objects or leaning on them with the hindquarters
- difficulty standing for the farrier
- resting with their legs under their body (like an elephant on a circus pedestal) or parked out
- nervous behavior with a tendency to excessive spooking
- coffee colored urine during serious episodes
- recumbency during particularly heavy episodes.


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.

PSSM1 has been identified in stock horse breeds such as the Quarter Horse, the Paint Horse and the American Appaloosa, but also in cold blood breeds such as Haflingers, Tinkers/Gypsy Cob Horses and Draft Horses.

Possible PSSM2 symptoms are quite similar to those associated with PSSM1. What seems to be fairly distinctive is that PSSM1 affected horses usually present with (often severely) elevated CK, LDH and/or AST levels, especially after exercise. In PSSM2 horses, these values are usually barely elevated at all. The majority of horses that have  PSSM type 1 have a history of multiple episodes of muscle stiffness when they start training. Horses that are less afflicted can have one or two attacks a year. It rarely occurs that PSSM leads to a horse not being able to stand. Coffee coloured urine is often seen as a result of muscle break down. Muscle enzymes get into the bloodstream and from there to the urine. When this happens the intensity of the attack should be taken very seriously as this can result in kidney failure. Young PSSM afflicted foals sometimes have symptoms like serious muscle pains and weakness. Mostly this occurs when the foal has another infection like diarrhoea or a cold.  Some foals and yearlings, especially suffering from PSSM2 , can show muscle stiffness and have trouble getting up during their daily activities.  At a later stage of the disease, PSSM2 often causes visible muscle damage and muscle wastage, gait abnormalities and shifting lameness for which there often is no clinical or radiological explanation. Horses with PSSM2 often present with very high muscle tension.  In some PSSM2 affected horses, muscle damage presents itself visibly in the form of dents and/or so called divots (named after the damage to the grass after taking a bad swing at the golf course), that tend to look like kick marks. These can happen quickly; horse owners report them occurring overnight.

Muscle damage can also take on the form of hard ripples or waves under the skin.  
Gait abnormalities can be expressed as rope walking (the horse places its feet in front of one another instead of beside on another), short gaits, tripping or stumbling, cross firing or disunited canter or bunny hopping: the horse moves both hind legs forward at the same time at the gallop. An uncoordinated way of going without the horse being technically lame can also be a symptom of PSSM2.

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.

PSSM and the heart


Many owners of PSSM afflicted horses are afraid the tying- up could also affect the heart. However in recent research in healthy and PSSM ( type 1) horses no clues were found that concludes that PSSM horses have more heart problems than non-afflicted horses. Most likely, this is due to the difference in structure of the muscle tissue in heart and skeleton muscles. There are three types of muscle tissue; 1, 2a en 2x. Type 1 mainly uses energy from the fatty acid metabolism, type 2a and 2x partly form the fatty acid metabolism but mainly form the glycogen metabolism. The heart muscle itself exists mainly of Type 1 tissue and because of that is much less sensitive to PSSM than 2a and 2x. Furthermore the researchers concluded that because of the hearts constant contractions, in contrast to the skeleton muscles which have resting periods the heart is less sensitive for the increase in sugars and because of that less sensitive to the accompanying muscle problems.