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 fromPubMedandVetMedResource.
  • Naylor R (2014)Managing muscle disease is horses.In Pract36(8), 418-423BMJ.
  • Baird J D, Valberg S J, Anderson S M, McCue M E & Mickelson J R (2010)Presence of the glycogen synthase 1 (GYS1) mutation causing type 1 polysaccharide storage myopathy in continental European draught horse breeds. Vet Rec167(20), 781-784PubMed.
  • Winjberg I D, Ruitenbeek W, Jansen G, Westermann C M & van der Kolk J H (2008)Myopathy in a Haflinger horse: An initiating search for a fatty acid oxidation deficiency.Equine Vet Educ20(10), 532-538WileyBlackwell.
  • Hunt L M, Valberg S J, Steffenhagen K & McCue M E (2008)An epidemiological study of myopathies in Warmblood horses.Equine Vet J40(2), 171-177PubMed.
  • Vercauteren G, van der Heyden S, Lefere L, Chiers K, Laevens H & Ducatelle R (2007)Concurrent atypical myopathy and equine dysautonomia in two horses.Equine Vet J39(5), 463-465PubMed.
  • 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 J38(6), 497-501PubMed.
  • 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 Sci24(4), 159-164VetMedResource.
  • Hahn C N (2003)Equine myopathies.Equine Vet Educ15(4), 188-189WileyBlackwell.
  • Valberg S Jet al(1998)Skeletal muscle metabolic response to exercise in horses with 'tying-up' due to polysaccharide storage myopathy.Equine Vet J31, 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 Practice13, 169-185PubMed.
  • Robinson H C (1991)Atypical myoglobinuria.Vet Rec128, 166PubMed.
  • Harris Pet al(1990)Atypical myoglobinuria alert.Vet Rec127, 603PubMed.
  • Whitwell K Eet al(1988)Atypical myoglobinuria - an acute myopathy in grazing horses.Equine Vet J20, 357-363PubMed.
  • Bramlage L R, Reed S M & Embertson R M (1985)Semitendinosus tenotomy for treatment of fibrotic myopathy in the horse.JAVMA186, 565-567PubMed.

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., Newmarket. 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, Missouri. pp 469-522.