Canis ISSN: 2398-2942

Masticatory myopathies

Synonym(s): Eosinophilic myositis

Contributor(s): Kyle Braund, Laurent Garosi

Introduction

  • Common: myopathy affecting muscles of mastication.
  • Signs: pain or difficulty opening mouth.
  • Cause: immune-mediated.
  • 2 syndromes recognized:
    • Acute - masticatory myositis (sometimes called 'eosinophilic myositis').
    • Chronic - atrophic myositis.
  • Treatment: immunosuppressive doses of corticosteroids in acute form and anti-inflammatory doses in chronic form.
  • Prognosis: acute - good; chronic - more guarded.

Pathogenesis

Etiology

  • Masticatory muscles contain a unique muscle fiber type (type 2M) that differs both histochemically and biochemically from the fiber types present in limb muscles (types 1A and 2A).
  • Immune-mediated. Auto-antibodies are directed against type 2M fibers (fiber type-specific autoantibodies) formed in masticatory muscles. These antigens may be shared with bacteria, possibly allowing urinary tract, skin, etc. infections to initiate an immunologic attack.

Pathophysiology

  • Myopathy of muscles of mastication producing pain and difficulty opening mouth.
  • Fibrosis of muscles in chronic form can lead to inability to open the mouth.

Timecourse

  • Acute onset followed by a 2-4 week clinical course.
  • Sometimes chronic course over several months without apparent acute signs.

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.
  • Pitcher G D & Hahn C N (2007) Atypical masticatory muscle myositis in three Cavalier King Charles Spaniel littermates. JSAP 48 (4), 226-228 PubMed.
  • Evans J et al (2004) Canine inflammatory myopathies: a clinico-pathologic review of 200 cases. JVIM 18 (5), 679-691 PubMed.
  • Melmed C et al (2004) Masticatory muscle myositis: pathogenesis, diagnosis and treatment. Comp Contin Educ Pract Vet 26 (8), 590-605 VetMedResource.
  • Braund K G (1997) Endogenous causes of myopathies in cats and dogs. Vet Med 92 (7), 618-628 VetMedResource.
  • Vilafranca M et al (1995) Muscle fiber expression of transforming growth factor-beta 1 and latent transforming growth factor-beta binding protein in canine masticatory myositis. J Comp Pathol 112 (3), 299-306 VetMedResource.

Other sources of information

  • Kornegay J N (1995) Disorders of the skeletal muscles. In:Textbook of Veterinary Internal Medicine. Eds Ettinger S J & Feldman E. W B Saunders, Philadelphia, pp 727-736.


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