Symptoms of Exertional Myopathy
The clinical presentation of exertional myopathy is highly diverse and may develop gradually and insidiously or manifest suddenly in a severe form. Further complicating the condition, multiple contributing factors of different origins are often involved simultaneously.
Similar clinical signs can be observed in all forms of exertional myopathy (MIM, PSSM, and RER), making differentiation between them challenging. The use of DNA testing helps to determine to what extent the known genetic factors are involved.
First Signs of Exertional Myopathy
- Refusal to strike off into canter
- Reluctance to move forward
- Stiff gait
- Appears difficult or impossible to train
- Intermittent mild lameness
- Excessive sweating
- Evasive behavior during saddling
Acute Manifestations
The first distinct, often severe symptoms usually appear following a trigger event (“stress”) and can transform a previously mild or entirely subclinical condition into an acute symptomatic episode. As a result of the painful muscles, the horse is then usually very uncooperative and may even become aggressive.
If, in addition to severe pain, dark brown urine and elevated CK levels are present, these would be the key symptoms suggesting acute RER (tying up). This condition is confirmed if the horse fully recovers after the episode. MIM and PSSM cases may gradually ease but affected horse may remain sensitive and easily fall back into the symptoms.
In cases involving MIM or PSSM, symptoms are observed to occur even under minimal exertion; horses do not recover as fully as they do with RER, and the condition often becomes chronic.
Indications of chronic Exertional Myopathy
If the pain persists and is accompanied by muscle wasting or a failure to build muscle, this would indicate chronic exertional myopathy.
If no testing for detectable DNA variants has been performed to date, such testing would be indicated to determine the extent to which the horse is affected.