Title | Suspected myofibrillar myopathy in Arabian horses with a history of exertional rhabdomyolysis. |
Publication Type | Journal Article |
Year of Publication | 2016 |
Authors | Valberg, SJ, McKenzie, EC, Eyrich, LV, Shivers, J, Barnes, NE, Finno, CJ |
Journal | Equine Vet J |
Volume | 48 |
Issue | 5 |
Pagination | 548-56 |
Date Published | 2016 Sep |
ISSN | 2042-3306 |
Keywords | Animals, Female, Genetic Predisposition to Disease, Horse Diseases, Horses, Male, Muscle, Skeletal, Myopathies, Structural, Congenital, Physical Endurance, Physical Exertion, Retrospective Studies, Rhabdomyolysis, Sports |
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. |
DOI | 10.1111/evj.12493 |
Alternate Journal | Equine Vet J |
PubMed ID | 26234161 |
PubMed Central ID | PMC4833696 |
Grant List | K01 OD015134 / OD / NIH HHS / United States L40 TR001136 / TR / NCATS NIH HHS / United States |