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 muscles
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.
