Skip to main content

Information for veterinarians

The disease classification of “Equine Exertional Myopathies, EEM” forms the most common group of muscle diseases.

Multiple underlying causes interact to result in a complex of symptoms that can include: muscle stiffness/tension, muscle cramping and/or fasciculations, reluctance to move, coordination problems (especially with gait changes), pain, exercise intolerance and even general weakness. Degenerative changes in the muscles may lead to focal (divots) or extensive muscle atrophy, as well as to muscle stiffness. Associated pain may lead to a refusal to perform or even aggression.

Acute, chronic, sporadic/recurring, and subclinical forms of progression merge into one another, further complicating diagnosis.

The differential diagnoses include:

I) Human influences: Nutrition, Training/Exercise, Rider

II) Metabolic conditions: age, stress (transport), weather, pregnancy

III) Diseases/Disorders

  • Lameness

  • Colic

  • Laminitis

  • Fractures

  • Pleuropneumonia

  • Tetanus

  • Arterial thrombosis

  • Neurological diseases

  • Intravascular haemolysis and biliruninuria

  • Rhabdomyolysis due to excessive exercise or infection (eg. Clostridium spp., influenza, Streptococcus equi, Sarcocystis, New Equine Virus)

  • Immune-mediated myopathies (eg. MYH1-Myopathy)

  • Nutritional myodegeneration (Vitamin E deficiency, Selenium deficiency)

  • Poisonings (eg. Toxic plants)

  • Tick-borne illnesses (eg. Borreliose)

List of defects/predispositions that can currently be examined by DNA test

  • Pharmacogenomic/Metabolic

    • Genes: RYR1 (Ryanodine receptor 1); Disease: Malignant Hyperthermia (MH); Alias: MH

  • Metabolic/Glycogen Storage

    • Gene: GYS1 (Glycogen Synthase 1); Disease: Polysaccharide Storage Myopathy 1 (PSSM1); Alias: P1

  • Immune-mediated Myopathies

    • Gene: MYH1 (Myosin Heavy Chain 1) | Disease: MYH1-Myopathy (MYHM)

  • Muscle Integrity Myopathies (MIM Complex) included in MIM-6Var-Test (previously “PSSM2-Test”)

    • Gene: MYOT (Myotilin); Disease: Myotilinopathy; Alias: P

    • Gene: FLNC (Filamin C); Disease: Filaminopathy; Alias: P3

    • Gene: MYOZ3 (Myozenin-3); Disease: Myozeninopathy; Alias: P4

    • Gene: CACNA2D3 (Calcium channel, voltage-dependent, alpha 2/delta subunit 3); Alias: Px

    • Gene: PYROXD1 (Pyridine nucleotide-disulphide oxidoreductase domain 1); Disease: PYROXD1-associated Myopathy; Alias: P8

    • Gene: COL6A3 (Collagen type 6 alpha 3); Disease: COL6-related Dystrophy; Alias: K1



Due to the large number of factors that can lead to Exertional Myopathy, it is important to investigate if there are genetic predispositions or defects when beginning the diagnostic process and when clarifying differential diagnoses.

With the knowledge of the genetic make-up of an animal, existing environmental or medical co-factors can be assessed on a case-specific basis to inform initial therapies and appropriate adjustments in the future.