Symptoms

The most obvious symptom of PSSM is the classic case of tying-up: the horse has clearly observable muscle stiffness, is sweating profusely and is reluctant to move. In severe cases, the horse can have dark or coffee coloured urine. Tying up is a common symptom of especially PSSM type 1 and the Px variant on the MIM panel. These symptoms are so obvious that they often lead to further investigation, among which testing for PSSM type 1.

However, more often, horses do not get to the point of a severe episode of tying-up, but rather display more vague and more difficult to diagnose symptoms, such as:
- general stiffness
- lameness that often comes and goes, seem to shift sides and legs and are difficult to diagnose
- moving “with the handbrake on”: the horse appears lazy of slow, while it does respond lightly to the rider’s cues.
- sweating more than seems reasonable
- repeated flehming
- pawing
- repeatedly wanting to lie down
- tense, drawn up belly, sometimes also kicking at the belly. A combination of the above symptoms can make it difficult to distinguish from colic
- cinchy and/or cold backed
- training doesn’t “stick” or the horse starts showing behaviours such as bucking, balking or rearing when asked to do tasks it had mastered
- muscle tremors or spasms that can occur all over the body, but are often seen on the shoulders, flank and neck
- the horse stretches out as if to urinate, but doesn’t or only urinates very small amounts (stallions/geldings)
- general signs of pain, such as pain face, separating itself from the herd, defeated posture
- rubbing its hind end or other parts of the body on objects or leaning/sitting on them
- high muscle tension/muscles hard to the touch
- difficulty standing and/or keeping feet up for the farrier
- tripping (similar to horses with navicular problems)
- difficulties standing in cross ties
- difficulties traveling: losing balance, especially in turns, restlessness while on the road, refusing to load
- difficulty lunging
- keeping nose on the ground for prolonged periods of time while being exercised
- difficulties loping; cross firing
- problems with collection
- difficulties backing up
- choke or difficulties swallowing
- sudden muscle decline for no reason
- standing camped out or under
- abnormal gaits like rope walking, uncoordinated movement, bunny hopping (especially horses with PSSM2/MIM)
- nervous or abnormally excitable behaviour
- in severe cases: falling down and/or becoming recumbent.

Note: this is NOT a checklist!

These are examples of possible symptoms. Symptoms express themselves differently in different horses and can be dependent on what variant(s) a horse carries, breed, age, management, etc. Over time, the gravity and expression of symptoms usually fluctuates, even within one and the same horse.

Many of the above mentioned symptoms describe general pain symptoms, which makes the condition difficult to diagnose. Often, horses that end up being diagnosed with PSSM2 have previously been diagnosed with colic, laminitis, stifle injuries, behavioural problems or exercise intolerance. Sometimes, even neurological problems have been suspected, because a horses seems to be losing control of its own body.  Symptoms of other diseases like Lyme disease, ECVM, Kissing Spines or ulcers can be very similar to those of PSSM2. Testing can offer valuable insights in the diagnostic process.

The symptoms of PSSM2 can be and often are very similar to those of PSSM1. However, there are a few ways in which PSSM2 presents itself differently compared to PSSM1:
- muscle enzymes (LDH and CK, sometimes also AST) in horses with PSSM1 can be extremely elevated after exercise (in cases of a complete episode of  tying-up LDH and/or CK can be literally off the charts) whereas these values are often only mildly elevated in symptomatic horses with PSSM2 (the exception being the Px variant, that is associated with Recurrent Exertional Rhabdomyolysis (RER) .
- a number of horses with PSSM2 develop a very particular kind of atrophy in the form of divots, often on the shoulders or the hind end. The term “divot” is a golfing term that describes a piece of turf having been whacked out of the ground with the head of the golf. It leaves a hole with a bit of turf (a bump) beside it. This kind of damage usually occurs in later stages of the disease. Washboard like ripples are also often seen in horses with PSSM2. They are often temporary but in some horses they end up being permanent.
- horses with PSSM2 often have very high muscle tone
- crookedness in the body that cannot be corrected with riding. This happens when muscle cramp or damage occurs on one side of the body.
- horses with PSSM1 often become symptomatic once they enter training. Horses with PSSM2 appear to take to training well and usually become symptomatic later in life, on average between age 7 and 10. Usually, there have been signs that “something is off” earlier in life.

Again, this is not a checklist, but a description of commonly observed symptoms.