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Equine Vet J. 2016 Sep;48(5):548-56. doi: 10.1111/evj.12493. Epub 2015 Sep 7.

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

Author information

1
Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, USA.
2
Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, USA.
3
Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, USA.

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.

KEYWORDS:

desmin; exertional rhabdomyolysis; horse; intermediate filaments; myofilaments

PMID:
26234161
PMCID:
PMC4833696
DOI:
10.1111/evj.12493
[Indexed for MEDLINE]
Free PMC Article

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