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

S. J. Valberg, E. C. McKenzie, L. V. Eyrich, J. Shivers, N. E. Barnes, Carrie J Finno

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

REASONS FOR PERFORMING STUDY: Although exertional rhabdomyolysis (ER) is common in Arabian horses, there are no dedicated studies describing histopathological characteristics of muscle from Arabian horses with ER.

OBJECTIVES: 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).

STUDY DESIGN: 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.

Original languageEnglish (US)
Pages (from-to)548-556
Number of pages9
JournalEquine Veterinary Journal
Volume48
Issue number5
DOIs
StatePublished - Sep 1 2016

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Arabian (horse breed)
rhabdomyolysis
Rhabdomyolysis
muscular diseases
Horses
horses
Glycogen
glycogen
Muscular Diseases
Polysaccharides
Myofibrillar Myopathy
Intervertebral Disc Degeneration
cytoskeletal proteins
Muscles
muscles
Cytoskeletal Proteins
polysaccharides
biopsy
electron microscopy
Electron Microscopy

Keywords

  • desmin
  • exertional rhabdomyolysis
  • horse
  • intermediate filaments
  • myofilaments

ASJC Scopus subject areas

  • Equine

Cite this

Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. / Valberg, S. J.; McKenzie, E. C.; Eyrich, L. V.; Shivers, J.; Barnes, N. E.; Finno, Carrie J.

In: Equine Veterinary Journal, Vol. 48, No. 5, 01.09.2016, p. 548-556.

Research output: Contribution to journalArticle

Valberg, S. J. ; McKenzie, E. C. ; Eyrich, L. V. ; Shivers, J. ; Barnes, N. E. ; Finno, Carrie J. / Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. In: Equine Veterinary Journal. 2016 ; Vol. 48, No. 5. pp. 548-556.
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N2 - REASONS FOR PERFORMING STUDY: Although exertional rhabdomyolysis (ER) is common in Arabian horses, there are no dedicated studies describing histopathological characteristics of muscle from Arabian horses with ER.OBJECTIVES: 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).STUDY DESIGN: 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.

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