ISSN 2398-2977      

Muscle: masseter myodegeneration / myositis

pequis

Introduction

  • Cause: nutritional myodegeneration linked to selenium deficiency and/or vitamin E deficiency in most cases.
  • Signs:
    • Acute: dysphagia, bilateral painful swelling of masseter muscles, salivation, tachycardia and arrhythmias, pigmenturia, difficulty moving.
    • Chronic: dysphagia, trismus, weight loss, teeth grinding, bilateral masseter muscle atrophy.
  • Diagnosis: clinical signs, increased muscle enzymes, low serum selenium/vitamin E values, masseter muscle biopsy.
  • Treatment: supportive treatment, eg analgesia, anti-inflammatories, fluid therapy; and selenium/vitamin E supplementation.
  • Prognosis: guarded for acute cases, but complete recovery is possible. Chronic cases may never regain the ability to eat normally.

Pathogenesis

Etiology

  • Suspected due to selenium   Selenium   and/or vitamin E   Vitamin E   deficiency.

Predisposing factors

General
  • Stress, such as late pregnancy, increased exercise.

Specific

  • Known region with soil deficient in selenium.
  • Management practices preventing access to suitable grazing and/or lack of mineral supplementation.

Pathophysiology

  • Vitamin E and selenium are essential antioxidants and have a role in protecting the cell membrane from peroxidation by free radicals; they are thought to prevent nutritional myodegeneration.
  • However, in horses affected with masseter myodegeneration, the measured values are not consistently low and supplementation does not always cure or prevent the condition.
  • Other factors such as stress and increased physical activity may be important for developement of clinical signs in the face of antioxidant deficiency.

Timecourse

  • Duration of selenium deficiency required to result in clinical signs is not known.

Epidemiology

  • All horses with a selenium deficient diet are at risk, however clinical cases of masseter myodegeneration/myositis are rarely reported.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Schefer K D, Hagen R, Ringer S K & Schwarzwald C C (2011) Laboratory, electrocardiographic, and echocardiographic detection of myocardial damage and dysfunction in an Arabian mare with nutritional masseter myodegeneration. J Vet Intern Med 25, 1171-1180 PubMed.
  • Conwell R C (2010) Hyperlipaemia in a pregnant mare with suspected masseter myodegeneration. Vet Rec 166, 116-117 PubMed.
  • Pearson E G, Snyder S P & Saulez M N (2005) Masseter myodegeneration as a cause of trismus or dysphagia in adult horses. Vet Rec 156, 642-646 PubMed.
  • Maylin G A, Rubin D S & Lein D H (1980) Selenium and vitamin E in horses. Cornell Vet 70, 272-289 PubMed.
  • Owen R, Moore J N, Hopkins J B & Arthur D (1977) Dystrophic myodegeneration in adult horses. JAVMA 171, 343-349 PubMed.
  • Wilson T M, Morrison H A, Palmer N C et al (1976) Myodegeneration and suspected selenium/vitamin E deficiency in horses. JAVMA 169, 213-217 PubMed.

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