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Equine veterinary journal2015; 48(5); 548-556; doi: 10.1111/evj.12493

Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis.

Abstract: Although exertional rhabdomyolysis (ER) is common in Arabian horses, there are no dedicated studies describing histopathological characteristics of muscle from Arabian horses with ER. Objective: To prospectively identify distinctive histopathological features of muscle from Arabian endurance horses with a history of ER (pro-ER) and to retrospectively determine their prevalence in archived samples from Arabian horses with exertional myopathies (retro-ER). Methods: Prospective and retrospective histopathological description. Methods: Middle gluteal muscle biopsies obtained from Arabian controls (n = 14), pro-ER (n = 13) as well as archived retro-ER (n = 25) muscle samples previously classified with type 2 polysaccharide storage myopathy (15/25), recurrent exertional rhabdomyolysis (7/25) and no pathology (3/25) were scored for histopathology and immunohistochemical staining of cytoskeletal proteins. Glutaraldehyde-fixed samples (2 pro-ER, one control) were processed for electron microscopy. Pro-ER and retro-ER groups were compared with controls using Mann-Whitney U and Fisher's exact tests. Results: Centrally located myonuclei in mature myofibres were found in significantly more (P<0.05) pro-ER (12/13) and retro-ER (21/25) horses than controls (4/14). Degenerating myofibres were not evident in any biopsies. Retro-ER horses had amylase-resistant polysaccharide (6/25, P<0.05) and higher scores for cytoplasmic glycogen, rimmed vacuoles and rod-like bodies. A few control horses (3/14) and significantly (P<0.05) more pro-ER (12/13) and retro-ER (18/25) horses had disrupted myofibrillar alignment and large desmin and αβ-crystallin positive cytoplasmic aggregates. Prominent Z-disc degeneration and focal myofibrillar disruption with regional accumulation of β-glycogen particles were identified on electron microscopy of the 2 pro-ER samples. Conclusions: In a subset of Arabian horses with intermittent episodes of exertional rhabdomyolysis, ectopic accumulation of cytoskeletal proteins and Z-disc degeneration bear a strong resemblance to a myofibrillar myopathy. While many of these horses were previously diagnosed with type 2 polysaccharide storage myopathy, pools of glycogen forming within disrupted myofibrils appeared to give the false appearance of a glycogen storage disorder.
© 2015 EVJ Ltd.
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Publication Date: 2015-09-07 PubMed ID: 26234161PubMed Central: PMC4833696DOI: 10.1111/evj.12493Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article focuses on a specific disorder, exertional rhabdomyolysis (ER), common in Arabian horses, with particular attention on the muscle characteristics. The researchers studied muscle biopsies from afflicted Arabian endurance horses to identify common histopathological features, and they compared these to archived samples to spot any patterns or consistencies.

Methods

  • The study is both prospective and retrospective i.e. it uses existing data and new findings to describe the muscle characteristics of afflicted Arabian horses.
  • The researchers collected muscle biopsies from controls (14 horses), pro-ER (13 horses) and retro-ER (25 horses). The archived retro-ER samples included horses previously diagnosed with type 2 polysaccharide storage myopathy, recurrent rhabdomyolysis, and those showing no pathologies.
  • The muscle samples were scored for histopathology, a microscopic examination of tissue, and for immunohistochemical staining of cytoskeletal proteins, a technique used to visualize proteins in cells.
  • For closer examination of muscle tissues, some samples were processed for electron microscopy, a technique that uses a beam of electrons to create an image of the sample.
  • Differences between the pro-ER and retro-ER groups were statistically analyzed against the controls using the Mann-Whitney U and Fisher’s exact tests.

Results

  • Centrally located myonuclei in mature muscle fibers were more common in pro-ER and retro-ER horses than in control horses.
  • There were no evident degenerating muscle fibers in any of the samples examined.
  • Retro-ER horses displayed amylase-resistant polysaccharide (hard to breakdown complex sugars) and higher levels of cytoplasmic glycogen, structural abnormalities in the form of rimmed vacuoles and rod-like bodies, all signs of muscle disorders.
  • A subset of control horses and significantly more pro-ER and retro-ER horses had disrupted muscle fiber alignment and large amounts of specific proteins (desmin and αβ-crystallin) in the cytoplasm of their cells.
  • The two pro-ER samples examined using electron microscopy displayed significant muscle fiber and Z-disc degeneration along with accumulated β-glycogen particles in certain regions.

Conclusions

  • The results showed that some Arabian horses with intermittent ER show muscle characteristics similar to a muscle disorder called myofibrillar myopathy.
  • While a number of these horses had been previously diagnosed with a different muscle disorder (type 2 polysaccharide storage myopathy), the study suggests that the glycogen observed could be due to the disruption of the muscles rather than an actual glycogen storage disorder.

Cite This Article

APA
Valberg SJ, McKenzie EC, Eyrich LV, Shivers J, Barnes NE, Finno CJ. (2015). Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. Equine Vet J, 48(5), 548-556. https://doi.org/10.1111/evj.12493

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 48
Issue: 5
Pages: 548-556

Researcher Affiliations

Valberg, S J
  • Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, USA.
McKenzie, E C
  • Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, USA.
Eyrich, L V
  • Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, USA.
Shivers, J
  • Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, USA.
Barnes, N E
  • Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, USA.
Finno, C J
  • Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, USA.

MeSH Terms

  • Animals
  • Female
  • Genetic Predisposition to Disease
  • Horse Diseases / genetics
  • Horse Diseases / pathology
  • Horses
  • Male
  • Muscle, Skeletal / pathology
  • Myopathies, Structural, Congenital / pathology
  • Myopathies, Structural, Congenital / veterinary
  • Physical Endurance
  • Physical Exertion
  • Retrospective Studies
  • Rhabdomyolysis / etiology
  • Rhabdomyolysis / veterinary
  • Sports

Grant Funding

  • K01 OD015134 / NIH HHS
  • L40 TR001136 / NCATS NIH HHS

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Citations

This article has been cited 8 times.
  1. Lindsay-McGee V, Massey C, Li YT, Clark EL, Psifidi A, Piercy RJ. Characterisation of phenotypic patterns in equine exercise-associated myopathies. Equine Vet J 2025 Mar;57(2):347-361.
    doi: 10.1111/evj.14128pubmed: 38965932google scholar: lookup
  2. Valberg SJ, Henry ML, Herrick KL, Velez-Irizarry D, Finno CJ, Petersen JL. Absence of myofibrillar myopathy in Quarter Horses with a histopathological diagnosis of type 2 polysaccharide storage myopathy and lack of association with commercial genetic tests. Equine Vet J 2023 Mar;55(2):230-238.
    doi: 10.1111/evj.13574pubmed: 35288976google scholar: lookup
  3. Henry ML, Velez-Irizarry D, Pagan JD, Sordillo L, Gandy J, Valberg SJ. The Impact of N-Acetyl Cysteine and Coenzyme Q10 Supplementation on Skeletal Muscle Antioxidants and Proteome in Fit Thoroughbred Horses. Antioxidants (Basel) 2021 Oct 30;10(11).
    doi: 10.3390/antiox10111739pubmed: 34829610google scholar: lookup
  4. Williams ZJ, Velez-Irizarry D, Gardner K, Valberg SJ. Integrated proteomic and transcriptomic profiling identifies aberrant gene and protein expression in the sarcomere, mitochondrial complex I, and the extracellular matrix in Warmblood horses with myofibrillar myopathy. BMC Genomics 2021 Jun 11;22(1):438.
    doi: 10.1186/s12864-021-07758-0pubmed: 34112090google scholar: lookup
  5. Valberg SJ, Finno CJ, Henry ML, Schott M, Velez-Irizarry D, Peng S, McKenzie EC, Petersen JL. Commercial genetic testing for type 2 polysaccharide storage myopathy and myofibrillar myopathy does not correspond to a histopathological diagnosis. Equine Vet J 2021 Jul;53(4):690-700.
    doi: 10.1111/evj.13345pubmed: 32896939google scholar: lookup
  6. Valberg SJ, Perumbakkam S, McKenzie EC, Finno CJ. Proteome and transcriptome profiling of equine myofibrillar myopathy identifies diminished peroxiredoxin 6 and altered cysteine metabolic pathways. Physiol Genomics 2018 Dec 1;50(12):1036-1050.
    doi: 10.1152/physiolgenomics.00044.2018pubmed: 30289745google scholar: lookup
  7. Williams ZJ, Bertels M, Valberg SJ. Muscle glycogen concentrations and response to diet and exercise regimes in Warmblood horses with type 2 Polysaccharide Storage Myopathy. PLoS One 2018;13(9):e0203467.
    doi: 10.1371/journal.pone.0203467pubmed: 30183782google scholar: lookup
  8. Valberg SJ, Nicholson AM, Lewis SS, Reardon RA, Finno CJ. Clinical and histopathological features of myofibrillar myopathy in Warmblood horses. Equine Vet J 2017 Nov;49(6):739-745.
    doi: 10.1111/evj.12702pubmed: 28543538google scholar: lookup
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