JPC SYSTEMIC PATHOLOGY
Musculoskeletal System
March 2019
M-M14

Signalment (JPC #1535964):  Five-year-old quarter horse mare

HISTORY:  This mare showed signs of "tying up" after being exercised. She became recumbent and began to pass coffee-colored urine.  The mare was euthanatized 8 days after onset of signs.  Clinical pathological findings include: BUN-25 (11-27); AST 1250 (160-412); ALT-1750 (no reference interval given); LDH-7200 (112-456).

HISTOPATHOLOGIC DESCRIPTION:  Skeletal muscle:  Multifocally and randomly affecting up to 75% of muscle fibers, individual myocytes are markedly swollen with pale vacuolated sarcoplasm (degeneration); hypereosinophilic, and hyalinzed with fragmented myofibrils, disruption of the endomysium, loss of cross-striations, occasional contraction bands, and nuclear pyknosis or karyolysis (necrosis); or lost with replacement by karyorrhectic debris, moderate numbers of macrophages and few fibroblasts.  Multifocally few myocytes have nuclear internalization and increased basophilia with rowing of nuclei that are large with prominent nucleoli (regeneration), and there is moderate proliferation of satellite cells.  Fibrin, edema, moderate numbers of histiocytes, lymphocytes and plasma cells multifocally infiltrate and expand the perimysium and endomysium.

MORPHOLOGIC DIAGNOSIS: Skeletal muscle:  Degeneration and necrosis, monophasic, multifocal, random, moderate, with myofiber regeneration, and moderate histiocytic and lymphoplasmacytic myositis, quarter horse, equine.

CONDITION:  Equine exertional rhabdomyolysis

SYNONYMS:  Exertional rhabdomyolysis syndrome (ERS), exertional myopathy, ‘tying-up’, ‘Monday-morning disease’, ‘set fast’, azoturia, black water, paralytic myoglobinuria

GENERAL DISCUSSION:

PATHOGENESIS:

TYPICAL CLINICAL FINDINGS:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Clinicopathological findings:

UltrastructurAL FINDINGS:

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

REFERENCES:

  1. Alexander AB, Hanley CS, Duncan MC, Ulmer K, Padilla LR. Management of acute renal failure with delayed hypercaclemia secondary to sarcocystis neurona-induced myositis and rhabdomyolysis in a California sea lion (Zalphus californianus). J Zoo Wildl Med. 2015; 46(3):652-656.
  2. Aleman M, Nieto JE, Magdesian KG. Malignant hyperthermia associated with ryanodine receptor 1 (C7360G) mutation in horses. J Vet Intern Med. 2009; 23:329-334.
  3. Chamizo VE, Acevedo LM, Rivero JL. Prevalence and clinical features of exertional rhabdomyolysis in Andalusian horses. Vet Rec. 2015; 177(2):48.
  4. Cooper BJ, Valentine BA. Muscle and tendon. In: Maxie MG, ed.  Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 1. 6th St. Louis, MO: Elsevier; 2016: 221-224.
  5. Dranchak PR, et al. Inheritance of recurrent exertional rhabdomyolysis in Thoroughbreds. J Am Vet Med Assoc. 2005; 227: 762-767.
  6. Hall RL, Bender HS. Muscle. In: Latimer KS, Mahaffey EA, Prasse KW, eds. Duncan and Prasse’s Veterinary Laboratory Medicine Clinical Pathology. 5th ed. Ames, IA: Wiley-Blackwell; 2011: 283-289.
  7. McCue ME, Armién AG, Lucio M, Mickelson JR, Valberg SJ. Comparative skeletal muscle histopathologic and ultrastructural features in two forms of polysaccharide storage myopathy in horses. Vet Pathol. 2009; 46(6): 1281-1291.
  8. Quist EM, Dougherty JJ, Chaffin MK, Porter BF. Diagnostic exercise: Equine rhabdomyolysis. Vet Pathol. 2011; 48(6): E52-E58.
  9. Valentine BA: Skeletal muscle. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017: 917, 925, 938-939.
  10. Wells RJ, Sedacca CD, Aman AM, Hackett TB, Twedt DC, Shelton GD. Successful management of a dog that had severe rhabdomyolysis with myocardial and respiratory failure. J Am Vet Med Assoc. 2009; 234(8): 1049-1054.
  11. Wilberger MS, et al. Prevalence of exertional rhabdomyolysis in endurance horses in the Pacific Northwestern United States. Equine Vet J. 2015;47(2): 165-170.
  12. Yazwinski M, Milizio JG, Wakshlag JJ. Assessment of serum myokines and markers of inflammation associated with exercise in endurance racing sled dogs. J Vet Intern Med. 2013; 27(2): 371-376.


Click the slide to view.



Click on image for diagnostic series.



Back | Home | Contact Us | Links | Help |