Introduction
- Cause : to date, a number of potential etiological and contributory factors were considered with reference to atypical myopathy or acquired Multiple Acyl-CoA Dehydrogenase Deficiency (MADD), but the exact etiology has remained unresolved yet.
- Signs : the main feature of this syndrome is the sudden onset of clinical signs characterized by acute generalized progressive myopathy.
- Diagnosis : should be based on the characteristic urinary profiles of organic acids (ethylmalonic acid and 2-methylsuccinic acid), glycine conjugates ((iso)valerate, butyrate and hexanoate) and predominantly short-chain acylcarnitines (acyl groups less than 10 carbon atoms) associated with Zenker necrosis/degeneration at histopathology.
- Treatment : intravenous administration of fluids enriched with glucose, insulin, vitamin B2, calcium and carnitine are suggested besides pain management using NSAIDs.
- Prognosis : the syndrome has a poor prognosis and is associated with a mortality rate of about 90% and death usually occurs within 72 h.
Diagnosis
Clinical signs
- The clinical signs are typical for any severe rhabdomyolysis, but not specific for atypical myopathy.
Diagnosis
Differential diagnosis
- Other non-exertional myopathies like vitamin E/selenium deficiency, glycogen branching enzyme deficiency, polysaccharide storage myopathy (PSSM), malignant hyperthermia, compartmental myopathy associated with anaesthesia, ionophore toxicosis, organophosphate toxicity, trauma, infectious and immune-mediated.
Sequelae
Prognosis
- Prognosis might be worsened by acute secondary renal tubular and liver necrosis due to myoglobinemia/uria.
- Associated with the mortality rate of about 90% and difficult confirmation of diagnosis there is no data on possible restoration of muscle function in severe cases.
Expected response to treatment
- Based on a mortality rate of about 90% and the absence of a causal therapy the expected response to treatment is poor.
Reasons for treatment failure
- Secondary renal tubular and liver necrosis as well as progressive degeneration of respiratory and cardiac muscles must be considered as most obvious reasons for treatment failure.
- Treatment failure might also be expected due to incomplete restoration of muscle function in severe cases following muscle fibrosis.
- Notwithstanding the very grave prognosis and a mortality rate of about 90% treatment failure might also be worsened by concurrent dysautonomia as has been reported in two cases.
Sources
Publications
Refereed papers
- Recent references from PubMed published during the last 12 months.
- Votion D M & Serteyn D (2008) Equine atypical myopathy: a review. Vet J (in press) PubMed.
- Votion D M, Linden A, Delguste C, Amory H, Thiry E, Engels P, van Galen G, Navet R, Sluse F, Serteyn D & Saegerman C (2008) Atypical myopathy in grazing horses: a first exploratory data analysis. Vet J (in press) PubMed.
- Westermann C M, Dorland L, Votion D M, de Sain-van der Velden M G M, Wijnberg I D, Wanders R J A, Spliet W G M, Testerink N, Berger N, Ruiter J P N & van der Kolk J H (2008) Acquired Multiple AcylCoA Dehydrogenase Deficiency in 10 horses with atypical myopathy. Neuromuscular Disorders 18 (5), 355-364 PubMed.
- van Galen G, Serteyn D, Amory H & Votion D M (2008) Atypical myopathy: new insights into the pathophysiology, prevention and management of the condition. Equine Vet Educ 20 (5), 234-238.
- Aleman M (2008) A review of equine muscle disorders. Neuromuscular Disorders 18 (4), 277-287 PubMed.
- Vercauteren G, van der Heyden S, Lefère L, Chiers K, Laevens H & Ducatelle R (2007) Concurrent atypical myopathy and equine dysautonomia in two horses. Equine Vet J 39 (5), 463-465 PubMed.
- Cassart D, Baise E, Cherel Y, Delguste C, Antoine N, Votion D M et al (2007) Morphological alterations in oxidative muscles and mitochondrial structure associated with equine atypical myopathy. Equine Vet J 39 (1), 26-32 PubMed.
- Westermann C M, de Sain-van der Velden M G M, van der Kolk J H, Berger R, Wijnberg I D, Koeman J P et al (2007) Equine biochemical Multiple Acyl-CoA Dehydrogenase Deficiency (MADD) as a cause of rhabdomyolysis. Molecular Genetics and Metabolism 91 (4), 362-369 PubMed.
- Votion D M, Linden A, Saegerman C, Engels P, Erpicum M, Thiry E, Delguste C, Rouxhet S, Demoulin V, Navet R, Sluse F, Serteyn D, van Galen G & Amory H (2007) History and clinical features of atypical myopathy in horses in Belgium (2000-2005). J Vet Int Med 21 (6), 1380-1391 PubMed.
- Votion D M, Hahn C N & Milne E M (2007) Concurrent conditions in single cases: the need to differentiate equine dysautonomia (grass sickness) and atypical myopathy. Equine Vet J 39 (5), 390-392 PubMed.
- Finno C J, Valberg S J, Wünschmann A & Murphy M J (2006) Seasonal pasture myopathy in horses in the midwestern United States: 14 cases (1998-2005). JAVMA 229 (7), 1134-1141 PubMed.
- Brandt K, Hinrichs U, Glitz F, Landes E, Schulze C, Deegen E et al (1997) Atypische Myoglobinurie der Weidepferde. Pferdeheilkunde 13, 27-34.
- Whitwell K E, Harris P & Farrington P G (1988) Atypical myoglobinuria: an acute myopathy in grazing horses. Equine Vet J 20, 357-363 PubMed.
- Bowen J N & Craig J F (1942) Myoglobinuria in horses. Vet Rec 35, 354-355.
Other sources of information
- Atypical Myopathy, Fr D Votion, Faculte de Medecine Veterinaire, Universite de Liege Departement des Sciences Cliniques, Pole equin Bat. B42, Boulevard de Colonster, 4000 Liege. Website: www.myopathieatypique.be.
