Myopathy in horses refers to a group of muscle disorders that affect the skeletal muscles, leading to symptoms such as weakness, stiffness, and muscle damage. These disorders can result from various causes, including genetic factors, nutritional deficiencies, metabolic imbalances, or external stressors. Myopathies can be classified into different types, such as exertional myopathies, which are related to physical activity, and non-exertional myopathies, which occur independently of exercise. Common forms of equine myopathy include polysaccharide storage myopathy (PSSM), recurrent exertional rhabdomyolysis (RER), and atypical myopathy. Diagnosis often involves clinical examination, muscle biopsy, and genetic testing. This page gathers peer-reviewed research studies and scholarly articles that explore the pathophysiology, diagnosis, and management of myopathy in horses, providing insights into the underlying mechanisms and therapeutic approaches.
Vercauteren G, van der Heyden S, Lefère L, Chiers K, Laevens H, Ducatelle R.This report concerns 2 horses that suffered typical clinical signs of atypical myopathy (AM) and equine grass sickness (EGS) concurrently. Clinical details and pathological lesions of the cases are described. EGS and AM are relatively rare diseases and the concurrency of the diseases in the same animals is therefore considered unlikely to be a coincidence. However, it is not suggested that the evidence shows a common aetiology but rather the existence of common predisposing causes.
Trim CM.Hemorrhagic myelopathy or myelomalacia is an uncommon cause of failure to stand after general anesthesia. Affected horses are usually young and have been anesthetized for relatively short times in dorsal recumbency. Clinical signs involve the hind limbs and include loss of deep pain perception. Etiology of this condition is not known. Differentiation from other forms of neuropathy and myopathy is important to the prognosis.
López JR, Linares N, Cordovez G, Terzic A.Exertional rhabdomyolysis is a myopathy of unknown pathophysiology. We measured intracellular resting calcium concentration ([Ca2+]i) by means of Ca(2+)-selective microelectrodes in intercostal muscle fibers from horses suffering from rhabdomyolysis, and from horses with no evidence of neuromuscular disorder. [Ca2+]i was several-fold higher in muscle fibers from horses suffering from rhabdomyolysis when compared to controls. Treatment of rhabdomyolytic horses with dantrolene, an agent that prevents Ca2+ release from the sarcoplasmic reticulum, reduced [Ca2+]i toward control values, and acceler...
Beech J, Lindborg S, Braund KG.Potassium concentrations were measured in semimembranosus muscle, plasma and erythrocytes, and the urinary fractional excretion determined in normal horses and those that had chronic intermittent exercise-associated rhabdomyolysis. Muscle from the rhabdomyolysis horses was also evaluated microscopically. The horses with rhabdomyolysis had a lower muscle potassium concentration on a dry weight basis. Although the wet weight potassium content was also lower, the difference was not significant. Urinary fractional excretion of potassium (and also sodium and chloride) did not differ significantly b...
Valverde A, Boyd CJ, Dyson DH, Pascoe PJ.Dantrolene, a drug used in the prevention and treatment of malignant hyperthermia, was believed responsible for prolonged postanesthetic recumbency in a horse. Prophylactically, dantrolene was given orally before induction of anesthesia. Dantrolene has been recommended for use in horses at risk of developing postanesthetic myopathy. Side effects, including ataxia, may result from dantrolene administration.
Bain FT, Merritt AM.To investigate the possibility that a disorder of potassium balance may have a role in the development of equine rhabdomyolysis, the potassium concentration within erythrocytes (RBC [K+]) and plasma (P [K+]) was measured in 3 groups of horses: group 1, eight 2-year-old fillies that had postexercise muscle soreness within 48 hours of sample collection; group 2, ten 2-year-old fillies subjected to identical management and training conditions (as fillies of group 1) and that did not have signs of myopathy; and group 3, 32 yearlings of both sexes on the farm of origin of groups 1 and 2 that were p...
Meijer AE, van den Hoven R, Wensing T, Breukink HJ.In this communication, the results of an enzyme histochemical study on m. gluteus medius of horses, sensitive to exertional myopathy, during attacks of rhabdomyolysis are presented. The activity and location of about 25 enzymes were examined. In the present report, the early metabolic changes are discussed. Within 6 min after an attack, some large rounded fibres (approximately 2%) were seen, which showed an intense red staining in the haematoxylin and eosin sections. These hypercontracted fibres showed an increase in activity of mitochondrial adenosine triphosphatase, indicating the presence o...
Muylle E, Vandenhende C, Oyaert W, Thoonen H, Vlaeminck K.Thirty-two horses were examined with a history of poor performance and unthriftiness several months after the ingestion of feed containing monensin sodium. Cardiac abnormality was diagnosed in 8 cases and suspected in 4 others. Necropsy examinations were performed on 6 cases with marked clinical symptoms and evidence of circulatory failure was found. Marked cardiac myopathy and fibrosis was a consistent feature. It is concluded that ingestion of monensin sodium by horses may cause either acute death or delayed cardiac circulatory failure as a result of specific cardiac myodegeneration.
Meijer AE, van den Hoven R, Wensing T, Breukink HJ.In this communication, the results of an enzyme histochemical study on m. gluteus medius of horses, sensitive to exertional myopathy, during attacks of rhabdomyolysis are presented. The activity and location of about 25 enzymes were examined. In the present report, the early metabolic changes are discussed. Within 6 min after an attack, some large rounded fibres (approximately 2%) were seen, which showed an intense red staining in the haematoxylin and eosin sections. These hypercontracted fibres showed an increase in activity of mitochondrial adenosine triphosphatase, indicating the presence o...
McKenzie RK, Gibson IR, Ritmeester A.Three weanling Thoroughbred fillies were presented during autumn with depression, muscle rigidity and, in one case, colic symptoms and cardiovascular shock. Results: All fillies had abnormal physical examinations that included elevated heart rates and respiratory rates coupled with muscle rigidity through the back and rump. Biochemistry revealed markedly elevated creatinine kinase and aspartate aminotransferase which indicated a myopathy. Methods: All three horses were diagnosed with presumptive equine atypical myopathy. The horses received supportive therapy as per the literature available at...
Valverde A, Boyd CJ, Dyson DH, Pascoe PJ.Dantrolene, a drug used in the prevention and treatment of malignant hyperthermia, was believed responsible for prolonged postanesthetic recumbency in a horse. Prophylactically, dantrolene was given orally before induction of anesthesia. Dantrolene has been recommended for use in horses at risk of developing postanesthetic myopathy. Side effects, including ataxia, may result from dantrolene administration.
Janzen N, Sander J, Terhardt M, Mallek M, Smith H, Witt P, Theelen MJP.The case of a young foal poisoned by maple toxin is described. It showed signs of myopathy caused by ingesting life-threatening amounts of maple toxin. Some maple trees (Acer species) can pose a health risk to grazing horses. The leaves, seeds and shoots contain hypoglycin A (HGA) and methylencyclopropylglycine (MCPRG) and can cause life-threatening atypical myopathy.
Vercauteren G, van der Heyden S, Lefère L, Chiers K, Laevens H, Ducatelle R.This report concerns 2 horses that suffered typical clinical signs of atypical myopathy (AM) and equine grass sickness (EGS) concurrently. Clinical details and pathological lesions of the cases are described. EGS and AM are relatively rare diseases and the concurrency of the diseases in the same animals is therefore considered unlikely to be a coincidence. However, it is not suggested that the evidence shows a common aetiology but rather the existence of common predisposing causes.
Bain FT, Merritt AM.To investigate the possibility that a disorder of potassium balance may have a role in the development of equine rhabdomyolysis, the potassium concentration within erythrocytes (RBC [K+]) and plasma (P [K+]) was measured in 3 groups of horses: group 1, eight 2-year-old fillies that had postexercise muscle soreness within 48 hours of sample collection; group 2, ten 2-year-old fillies subjected to identical management and training conditions (as fillies of group 1) and that did not have signs of myopathy; and group 3, 32 yearlings of both sexes on the farm of origin of groups 1 and 2 that were p...
Beech J, Lindborg S, Braund KG.Potassium concentrations were measured in semimembranosus muscle, plasma and erythrocytes, and the urinary fractional excretion determined in normal horses and those that had chronic intermittent exercise-associated rhabdomyolysis. Muscle from the rhabdomyolysis horses was also evaluated microscopically. The horses with rhabdomyolysis had a lower muscle potassium concentration on a dry weight basis. Although the wet weight potassium content was also lower, the difference was not significant. Urinary fractional excretion of potassium (and also sodium and chloride) did not differ significantly b...
Lotstra RJ, van den Broek J, Power T, Marr CM, Wijnberg ID.Atrial fibrillation is a common equine arrhythmia. Quinidine alone, or with digoxin are common treatments. Studies on outcome in Warmblood populations in which duration of the AF is often unknown are limited. Objective: To identify the factors that are associated with the success of full treatment cardioversion with oral medication, and establish whether there are differences in these factors between institutions. Methods: Retrospective case series using patient records of Equine University Clinic of Utrecht University and Rossdales Equine Hospital, Newmarket. Methods: Forty-nine horses treate...
Loomes K, de Grauw J, Gozalo-Marcilla M, Redondo JI, Bettschart-Wolfensberger R.Equine post-operative morbidity represents a significant concern for both veterinary surgeons and horse owners. Objective: To estimate the prevalence of post-operative complications in horses after elective/non-abdominal surgery or colic surgery. Methods: Systematic review. Methods: A database search identified eligible studies which reported the prevalence of equine post-operative complications published as a full paper in English in a peer-reviewed journal between 2000 and 2023. Studies were evaluated using the JBI Critical Appraisal Checklist for Prevalence Studies and GRADE (Grading of Rec...
