Masticatory Muscle Myositis

Masticatory Muscle Myositis

By: Dr. Erika de Papp

Section: Overview

Masticatory muscle myositis (MMM) is an inflammatory condition involving the muscles of mastication or chewing in the dog. MMM is caused by an immune mediated process targeted against specific muscle fibers; the immune system attacks the body's own muscles.

MMM occurs in all breeds of dog, but appears to be more common in German shepherds, Doberman pinschers and retrievers. Young and middle-aged dogs are most commonly affected. MMM has not been reported in the cat.

The disease occurs in both acute (sudden) and chronic forms, and the signs may vary with each form. The chronic form is seen more commonly.

What to Watch For

  • Swelling associated with facial and forehead muscles
  • Fever
  • Pain upon opening the mouth
  • Reluctance to eat or chew
  • Excessive salivation
  • Bulging of the eyes
  • Prolapse (protrusion) of the third eyelids
  • Shrinkage of head mu
    scles
  • Inability to open the mouth normally

    The latter two signs are recognized the most often, as they are associated with the chronic form of the disease.

    Diagnosis

  • History and physical exam
  • Complete blood count (CBC)
  • Biochemical profile
  • Serum creatine kinase
  • Serum type 2M myosin antibody titer
  • Muscle biopsy and immunocytochemistry
  • Electromyography (EMG)
  • Skull and dental radiographs (X-rays) or other imaging modality such as CT scan

    Treatment

  • Immunosuppressive doses of corticosteroids
  • Additional immunosuppressive drugs if clinically indicated

    Dogs that are severely affected and not immediately responsive to medical management may require a feeding tube.

    Home Care and Prevention

  • Recheck examination every 3 to 4 weeks during the first several months of therapy is important to monitor response to treatment and allow the veterinarian to taper the medications appropriately. In many cases, long-term or even lifelong therapy may be necessary.

  • Feeding soft foods at home until the dog's signs have improved is imperative. Home management of a feeding tube may be required as well.

  • Avoidance of rawhides or other chew toys is advisable.

  • There are no preventative measures to reduce risk of MMM.

     
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