equis - Articles
Muscle: myopathy – overview
Synonym(s): Muscle myopathy
Introduction
- 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 or stiffness on exercise, gait abnormality, muscle weakness, tremor or fasciculations, local or generalized muscle dysfunction; pain and associated systemic signs, eg colic, sweating, increased heart and respiratory rates increased body temperature; local swellings; generalized or specific muscle wastage or atrophy; myoglobinuria, recumbency, exercise intolerance, reluctance to collect or difficulty holding a canter, sudden death.
- Diagnosis: physical examination including palpation of muscles, exercise challenge tests, biochemical tests including CK CSF: creatine kinase and AST analysis Blood: biochemistry - aspartate amino transferase (AST), urinalysis Urine: overview, genetic tests, diagnostic imaging (thermography Thermography, electromyography Electrodiagnostic testing, scintigraphy Bone: scintigraphy, ultrasonography Ultrasonography: overview), muscle biopsy Muscle: biopsy.
- Treatment: symptomatic and supportive, eg analgesia, sedation, fluid therapy Fluid therapy: overview, selenium Selenium and vitamin E Vitamin E therapy; specific, eg diet and exercise regimens, surgery.
- Prognosis: depends on etiology and severity; generally guarded.
- Myopathies include:
- Exertional rhabdomyolysis Muscle: myopathy - exertional rhabdomyolysis.
- Polysaccharide storage myopathy types 1 and 2 Muscle: myopathy - exertional rhabdomyolysis.
- Myofibrillar myopathy.
- Glycogen branching enzyme myopathy Muscle: glycogen branching enzyme deficiency (GBED).
- Myosin heavy chain myopathy.
- Fibrotic and ossifying myopathy Muscle: myopathy - fibrotic.
- Post-anesthetic myopathy Muscle: myopathy - postanesthetic.
- Hyperkalemic periodic paralysis Muscle: hyperkalemic periodic paralysis.
- Atypical myoglobinuria Atypical myoglobinuria.
- White muscle disease of foals.
- Nutritional myopathies Nutrition: nutritional myopathy.
Breed/Species predisposition
- Quarterhorses Quarterhorse:
- Polysaccharide storage myopathy Muscle: myopathy - exertional rhabdomyolysis.
- Myosin heavy chain myopathy.
- Immune-mediated polymyositis Immune-mediated disease: overview.
- Hyperkalemic periodic paralysis Muscle: hyperkalemic periodic paralysis.
- Malignant hyperthermia Malignant hyperthermia.
- Glycogen branching enzyme deficiency Muscle: myopathy - exertional rhabdomyolysis.
- Thoroughbreds Thoroughbred - recurrent exertional rhabdomyolysis Muscle: myopathy - exertional rhabdomyolysis.
- Draft horses, Belgian and Percheron draft breeds Irish Draft - Equine polysaccharide storage myopathy Muscle: myopathy - exertional rhabdomyolysis.
Cost considerations
- Costs of loss of use during episodes of muscle disease.
- Costs of diagnostic work-up, treatment and management of disease.
- Loss of breeding potential in genetically transmitted diseases.
Special risks
- Malignant hyperthermia Malignant hyperthermia.
- Post-anesthetic myopathy Muscle: myopathy - postanesthetic.
Pathogenesis
Etiology
- Neurogenic or myogenic.
- A field of considerable recent and ongoing research.
- Some syndromes are multifactorial and difficult to specifically define etiology.
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.
Myogenic
- Traumatic, eg Fibrotic myopathy Muscle: myopathy - fibrotic, muscle rupture (gastrocnemius, serratus ventralis).
- Inflammatory, eg muscle sprain.
- Infectious:
- Bacterial, eg Clostridial myonecrosis Clostridia spp, Streptococcus spp Streptococcus spp, Staphylococcal spp Staphylococcus spp, Corynebacterium pseudotuberculosis Lymphangitis.
- Viral, eg equine influenza Equine influenza virus, herpes virus Equine herpesvirus.
- Parasitic, eg Sarcocystis spp Sarcocystis neurona, Trichinella spiralis.
- Toxic, eg white snakeroot, ionophores (certain coccidiostats), Cassia occidentalis (Senna).
- Hormonal, eg ? hypothyroidism.
- Circulatory, eg post-anesthetic myositis Muscle: myopathy - postanesthetic, aortic-iliac thrombosis Cardiovascular: aortoiliac thrombosis.
- Genetic:
- Enzyme deficiencies (glycogen branching, mitochondrial).
- Myotonias (hyperkalemic periodic paralysis Muscle: hyperkalemic periodic paralysis, myotonia congenital, myotonia dystrophy).
- Glycogen storage disorders (polysaccharide storage myopathy in Quarterhorses and Draft horses).
- Recurrent exertional rhabdomyolysis Muscle: myopathy - exertional rhabdomyolysis.
- Nutritional, eg vitamin E/selenium deficiency Nutrition: nutritional myopathy, motor neuron disease Neurology: motor neuron disease, degenerative myelopathy, selenium deficiency Nutrition: nutritional myopathy, malnutrition Weight loss: overview, thiamine deficiency Vitamin B1, electrolyte deficiency Musculoskeletal: nutritional deficiencies, carbohydrate overloading Nutrition: energy.
- Malignancy, eg muscle tumors.
- Miscellaneous:
- Overexertion.
- Cachexia.
- Disuse atrophy.
- Idiopathic, eg atypical myoglobinuria Atypical myoglobinuria, polymyopathy.
Post-anesthetic myopathy Muscle: myopathy - postanesthetic
- Direct pressure on muscle or subcutaneous nerves which is increased in heavier animals, those with increased muscular development, increased recumbency periods, and poor padding and positioning on the anesthetic table.
- Hypotension Anesthesia: monitoring - cardiac output and blood pressure which is increased in long duration anesthesia, positive pressure ventilation Anesthesia: ventilators - overview, and poor positioning.
Exertional rhabdomyolysis Muscle: myopathy - exertional rhabdomyolysis
- Multifactorial: irregular exercise, dietary imbalances, possibly genetic in some individuals.
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
- Ingestion of toxin hypoglycin A found in seeds, leaves and seedlings of trees of the genus Acer (maples). In UK, Acer pseudoplatanus, and in North America Acer negundo.
- Associated with stressful environmental conditions and low plane of nutrition.
White muscle disease of foals Nutrition: nutritional myopathy
- Selenium deficiency plus as yet unknown factors → failure to protect muscle cell membranes from peroxidative damage.
Diagnosis
Subscribe To View
This article is available to subscribers.
Try a free trial today or contact us for more information.
Treatment
Subscribe To View
This article is available to subscribers.
Try a free trial today or contact us for more information.
Prevention
Subscribe To View
This article is available to subscribers.
Try a free trial today or contact us for more information.
Outcomes
Subscribe To View
This article is available to subscribers.
Try a free trial today or contact us for more information.
Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Valberg S J (2020) Genetics of equine muscle disease. Vet Clin North Am Equine Pract 36 (2), 353-378 PubMed.
- Noll C V (2019) Standing myotomy to treat fibrotic myopathy: 22 cases (2004-2016) Vet Surg 48 (6), 997-1004 PubMed.
- Valberg S J (2018) Muscle conditions affecting sport horses. Vet Clin North Am Equine Pract 34 (2), 253-276 PubMed.
- Durward-Akhurst S A & Valberg S J (2018) Immune-mediated muscle diseases of the horse. Vet Pathol 55 (1), 68-75 PubMed.
- Lewis S S et al (2017) Clinical characteristics and muscle glycogen concentrations in warmblood horses with polysaccharide storage myopathy. Am J Vet Res 78 (11), 1305-1312 PubMed.
- Gonzalez-Medina, S et al (2017) Equine atypical myopathy in the UK: Epidemiological characteristics of cases reported from 2011 to 2015 and factors associated with survival. Equine Vet J 49 (6), 746-752 PubMed.
- Valberg S J et al (2016) Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. Equine Vet J 4