Rhabdomyolysis in horses is a condition characterized by the breakdown of muscle tissue, leading to the release of intracellular contents into the bloodstream. This condition can result from various factors, including overexertion, dietary imbalances, and genetic predispositions. Clinical signs often include muscle stiffness, pain, and weakness, and in severe cases, it may lead to kidney damage due to the release of myoglobin. Diagnosis typically involves clinical evaluation, blood tests for muscle enzymes, and urinalysis. Management strategies focus on addressing the underlying cause, providing supportive care, and implementing dietary and exercise modifications. This entry compiles peer-reviewed research studies and scholarly articles that explore the pathophysiology, diagnosis, and management of rhabdomyolysis in horses.
Beech J, Lindborg S, Fletcher JE, Lizzo F, Tripolitis L, Braund K.Muscle from horses with intermittent exercise associated rhabdomyolysis was examined to determine if calcium regulation was abnormal. In vitro studies on semimembranosus muscle fibre bundles showed the time to 50 per cent relaxation of caffeine-induced contractures was shorter and the electrically elicited twitch longer in horses with exercise associated rhabdomyolysis. Substitution of strontium for calcium eliminated the difference in caffeine contracture between the normal and rhabdomyolysis horses. The threshold of calcium-induced calcium release was lower than normal in terminal cisternae-...
Holmgren N, Valberg S.Quantitative immunodiffusion in one dimension was performed in 6-mm Duran tubes containing a 1% Nobel agar solution and various dilutions of antisera. A series of dilutions of pure myoglobin in equine sera as well as plasma from horses with rhabdomyolysis were tested. Standard curves were prepared of the migration distance of the formed precipitate from the meniscus of the gel after 3, 6, 12, and 24 hours. The clearest line of precipitate was formed with a 1:20 dilution of antisera in agar. Standard curves were nonlinear and plasma myoglobin could be detected at 2 micrograms of myoglobin/ml or...
Harris P, Marlin D, Gray J.A similar and significant (P less than 0.001) increase in plasma thyroxine (T4) concentration was seen in seven clinically normal thoroughbred horses 2 h after the intravenous administration of either 2.5 iu or 5 iu of thyroid stimulating hormone (TSH) with a peak response around 4 h after administration. The intravenous administration of 0.2, 0.5 or 1 mg thyrotrophin releasing hormone (TRH) resulted in a significant (P less than 0.01) increase in T4 concentration in three groups of animals; six thoroughbreds in full work, five thoroughbreds at rest and four ponies at rest. The peak response w...
Morris E, Seeherman HJ, O'Callaghan MW, Schelling SH, Paradis MR, Steckel RS.The uptake of the bone-seeking radiopharmaceutical 99mTc-MDP by damaged skeletal muscle in horses is evaluated. Twenty-four hours following strenuous exercise, 109 racehorses with a history of inadequate athletic performance and subtle lameness were imaged using scintigraphic techniques. Ten horses (9.2 per cent) demonstrated abnormal uptake of the radioisotope within skeletal muscles. A muscle biopsy from one of these horses confirmed that the muscles with increased scintigraphic activity had histologic evidence of rhabdomyolysis. This technique allows localisation and relative quantification...
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...
Beech J, Fletcher JE, Lizzo F, Johnston J.In vitro twitch characteristics of the semimembranosus muscle were evaluated in 9 clinically normal horses, in 15 horses with chronic intermittent rhabdomyolysis (CIR) and in 2 horses with myotonia. Effects of phenytoin on in vitro muscle twitch and clinical signs of CIR and myotonia were evaluated in these same horses. Times to 90% relaxation were prolonged in the horses with CIR (mean +/- SEM, 186 +/- 5.9 ms) and in 2 horses with myotonia (197 and 177 ms) compared with those in clinically normal horses (mean +/- SEM, 146 +/- 2.1 ms). Horses with CIR also had significantly (P less than 0.05) ...
Kruse CJ, Dieu M, Renaud B, François AC, Stern D, Demazy C, Burteau S, Boemer F, Art T, Renard P, Votion DM.Equine atypical myopathy (AM) is a severe environmental intoxication linked to the ingestion of protoxins contained in seeds and seedlings of the sycamore maple (Acer pseudoplatanus) in Europe. The toxic metabolites cause a frequently fatal rhabdomyolysis syndrome in grazing horses. Since these toxic metabolites can also be present in cograzing horses, it is still unclear as to why, in a similar environmental context, some horses show signs of AM, whereas others remain clinically healthy. Label-free proteomic analyses on the serum of 26 diseased AM, 23 cograzers, and 11 control horses were per...
Pruitt BN.Rhabdomyolysis in equines occurs in horses due to physical overexertion or underlying pathologic myopathy. Methocarbamol is a muscle relaxant that can be used in equines to treat symptoms associated with Rhabdomyolysis. Methocarbamol is available as a solution for injection but is not commercially available as an oral suspension. This article focuses on the treatment of Tying-up caused by overexertion, and details the treatment of Rhabdomyolysis with an oral suspension that was prepared for a veterinarian by a compounding pharmacist.
Andrews FM.Early aggressive medical therapy in horses with acute rhabdomyolysis is essential to prevent further muscle damage and secondary complications, such as laminitis and acute renal failure. A variety of pharmacologic agents may be helpful in the treatment of this condition but may have adverse affects if hydration status is not corrected first or concurrently with oral or intravenous fluids. Early aggressive therapy will help prevent irreversible muscle damage that could lead to poor performance in the future.
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...
Tosi I, Art T, Cassart D, Farnir F, Ceusters J, Serteyn D, Lemieux H, Votion DM.Polysaccharide storage myopathy (PSSM) is a widely described cause of exertional rhabdomyolysis in horses. Mitochondria play a central role in cellular energetics and are involved in human glycogen storage diseases but their role has been overlooked in equine PSSM. We hypothesized that the mitochondrial function is impaired in the myofibers of PSSM-affected horses. Nine horses with a history of recurrent exercise-associated rhabdomyolysis were tested for the glycogen synthase 1 gene (GYS1) mutation: 5 were tested positive (PSSM group) and 4 were tested negative (horses suffering from rhabdomyo...
Valberg SJ, Clancey NP, Salinger A, Waldridge B, Tan JY, Barton MH.To investigate pseudohyperkalemia occurring in horses experiencing rhabdomyolysis when serum chemistry profiles are run on an VetScan VS2 analyzer (Abaxis). Methods: 18 horses with rhabdomyolysis (creatine kinase [CK] > 1,000 U/L). Methods: In 3 horses with serum CK activities > 5,800 U/L and persistent serum potassium concentrations of > 8.5 mmol/L (VetScan VS2), potassium concentrations were reevaluated with either i-STAT Alinity Base Station (Abbott), Catalyst (Idexx), or Cobas c501 (Roche) ion-specific analyzers. Paired serum samples from 15 additional horses (median serum CK acti...
Hepworth-Warren KL, Goldsmith D, Tsoi M, Gerras A, Noll C, Pinn-Woodcock T, Moreira A, Penttila K, Ballou ME, Dembek KA, Valberg SJ.To describe the clinical findings, outcomes, and muscle histopathology in warmblood horses that developed severe rhabdomyolysis in the perianesthetic period despite remaining stable while under general anesthesia. Methods: 7 warmblood horses, 6 geldings and 1 mare, with a median age of 9 years (range, 4 to 18 years) and median weight of 615 kg (range, 550 to 703 kg). Records from the Valberg Neuromuscular Diagnostic Laboratory and Michigan State University were reviewed (2016 to 2023) to identify warmbloods with postanesthetic myopathy (PAM). Methods: Warmblood horses with no history of myopat...
