(MMM)

  • Occurs in dogs
  • Tends to affect the masseter and temporalis muscles
  • Autoantibodies selectively attack muscles of mastication (type IIM fibres)
  • Acute stage = eosinophilic myositis
    • Extremely swollen, painful, hard masticatory muscles
  • Chronic stage = atrophic myositis
    • Atrophy may occur without previous acute stage
  • Grossly:
    • Bilateral but not necessarily symmetrical
    • At first, enlarged and oedematous muscles becominf dark red, firm with reddish streaks and yellowiss foci
  • Histologically:
    • Acute lesions:
    • Chronic stage:
      • Atrophy predominates
      • Fasciculi are shrunken
      • Condensation of stroma -> enlarged endomysium
      • Focal plasma cell and lymphocyte infiltration