Equis ISSN 2398-2977

Muscle: myopathy - overview

Synonym(s): Muscle myopathy

Contributor(s): Steve Adair, Graham Munroe, Vetstream Ltd


  • Cause: neurogenic: hereditary or environmental, acquired or congenital; myogenic: trauma, inflammatory, infectious, toxic, hormonal, circulatory, genetic, nutritional, exercise-related, cachectic, malignancy, disuse.
  • Signs: muscle cramps on exercise, gait abnormality, muscle weakness, tremor, local or generalized muscle dysfunction; pain and associated systemic signs, eg colic, increased heart and respiratory rates increased body temperature; local swellings; muscle wastage; myoglobinuria, recumbency, sudden death.
  • Diagnosis: physical examination, exercise tests, biochemical tests, genetic tests, diagnostic imaging (thermography, electromyography, scintigraphy, ultrasonography), muscle biopsy.
  • Treatment: symptomatic and supportive, eg analgesia, sedation, fluid therapy; specific, eg diet and exercise, surgery.
  • Prognosis: depends on etiology and severity; generally guarded.
  • Myopathies include:



  • Neurogenic or myogenic.
  • A field of considerable ongoing research.
  • A firm etiologic basis for many causes of rhabdomyolysis has yet to be described.
  • Evidence is emerging for 3 immune-mediated syndromes: severe rhabdomyolysis and infarctive purpura (both associated withStreptococcus equi  Streptococcus spp  exposure) and immune-mediated polymyositis of Quarterhorses.

Neurogenic(hereditary or environmental, acquired or congenital)

  • Peripheral neuropathies.
  • Neuromuscular transmission disorders, eg Botulism   Botulism  , Tetanus   Tetanus  .
  • Anterior horn cell disorders.
  • Motor nerve root disorders.


Post-anesthetic myopathy  Muscle: myopathy - postanesthetic 

Exertional rhabdomyolysis  Muscle: myopathy - exertional rhabdomyolysis 

  • Multifactorial: irregular exercise, dietary imbalances, hormonal, metabolic.

Hyperkalemic periodic paralysis  Muscle: hyperkalemic periodic paralysis 

  • Genetic defect   →   abnormality in sodium channel transport.

Fibrotic and ossifying myopathy  Muscle: myopathy - fibrotic 

  • Trauma to semitendinosis   →   contracture.

Atypical myoglobinuria  Atypical myoglobinuria 

  • Unknown.
  • Associated with stressful environmental conditions and low plane of nutrition.

White muscle disease of foals  Nutrition: nutritional myopathy 

  • Selenium deficiency   →   failure to protect muscle cell membranes from peroxidative damage.

Storage myopathy  Muscle: myopathy - exertional rhabdomyolysis 

  • Glycogen and polysaccharide accumulation in muscle due to excessive synthesis.
  • Signs similar to exertional rhabdomyolysis.
  • Recurrent attacks.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Naylor R (2014) Managing muscle disease is horses. In Pract 36 (8), 418-423 BMJ.
  • Baird J D, Valberg S J, Anderson S M et al (2010) Presence of the glycogen synthase 1 (GYS1) mutation causing type 1 polysaccharide storage myopathy in continental European draught horse breeds. Vet Rec 167 (20), 781-784 PubMed.
  • Winjberg I D, Ruitenbeek W, Jansen G et al (2008) Myopathy in a Haflinger horse: An initiating search for a fatty acid oxidation deficiency. Equine Vet Educ 20 (10), 532-538 WileyBlackwell.
  • Hunt L M, Valberg S J, Steffenhagen K & McCue M E (2008) An epidemiological study of myopathies in Warmblood horses. Equine Vet J 40 (2), 171-177 PubMed.
  • Vercauteren G, van der Heyden S, Lefere L et al (2007) Concurrent atypical myopathy and equine dysautonomia in two horses. Equine Vet J 39 (5), 463-465 PubMed.
  • Franci P, Leece E A & Brearley J C (2006) Post anesthetic myopathy/neuropathy in horses undergoing magnetic resonance imaging compared to horses undergoing surgery. Equine Vet J 38 (6), 497-501 PubMed.
  • Aupperle H, Borgel C, Raila G & Schoon H-A (2004) Morphological, immunohistochemical and ultrastructural findings in an embryonal rhabdomyosarcoma of a newborn Thoroughbred foal. J Equine Vet Sci 24 (4), 159-164 VetMedResource.
  • Hahn C N (2003) Equine myopathies. Equine Vet Educ 15 (4), 188-189 WileyBlackwell.
  • Valberg S J et al (1998) Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy. Equine Vet J 31, 43-47 (Defines the metabolic events in exertional rhabdomyolysis caused by storage disease) PubMed.
  • Lofstedt J (1997) White muscle disease of foals. Vet Clin N Am Equine Practice 13, 169-185 PubMed.
  • Robinson H C (1991) Atypical myoglobinuria. Vet Rec 128, 166 PubMed.
  • Harris P et al (1990) Atypical myoglobinuria alert. Vet Rec 127, 603 PubMed.
  • Whitwell K E et al (1988) Atypical myoglobinuria - an acute myopathy in grazing horses. Equine Vet J 20, 357-363 PubMed.
  • Bramlage L R, Reed S M & Embertson R M (1985) Semitendinosus tenotomy for treatment of fibrotic myopathy in the horse. JAVMA 186, 565-567 PubMed.

Other sources of information

  • Various Authors (2005) Endurance and Sports Horse Session. In: Handbook of Presentations and Free Communications BEVA Congress 2005. Equine Veterinary Journal Ltd., UK. pp 78, 83, 86, 99.
  • MacLeay J M (2004) Diseases of the Musculoskeletal System. In: Equine Internal Medicine. Eds: Reed S M, Bayly W M & Sellon D C. Saunders, USA. pp 469-522.